JP2002082280A - Optical pickup device, opjective lens and beam expander - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical pickup device and an optical system capable of effectively correcting the variation of a spherical aberration generated due to the mode hop of a semiconductor laser. SOLUTION: Since a means (negative lens 4) for correcting the variation of a spherical aberration generated in an objective lens 3 is arranged between a light source 11 to be the semiconductor laser and the objective lens 3, the variation of the spherical aberration of the lends 3 due to the variation of oscillation wavelength can be effectively suppressed even when the variation of oscillation wavelength is generated due to the generation of a mode hop phenomenon or the like in the laser 11. Even when a change of the refractive index of the lens 3 is generated in accordance with a change in ambient temperature or humidity, the variation of the spherical aberration of the lens 3 which is generated due to the change can be effectively suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an optical pickup device, an objective lens, and a beam expander, and more particularly, to an optical pickup device, an objective lens, and a beam expander that can effectively correct fluctuations in spherical aberration.

[0002]

2. Description of the Related Art In recent years, with the practical use of a short-wavelength red semiconductor laser, a high-density optical disk having a size similar to that of a conventional optical disk, ie, a CD (compact disk) which is an optical information recording medium and having a large capacity. The development of DVDs (Digital Versatile Discs) is progressing, but it is expected that higher density next generation optical discs will appear in the near future. In the optical system of an optical information recording / reproducing apparatus using such an optical disk as a medium, in order to increase the density of a recording signal or reproduce a high-density recording signal, light is focused on a recording medium via an objective lens. It is required to reduce the spot diameter to be formed. To do this,
There is a fact that the wavelength of a laser as a light source is becoming shorter and the NA of an objective lens is becoming higher.

[0003]

By the way, as the wavelength of the laser is shortened and the NA of the objective lens is increased as described above, information is recorded or reproduced on or from a conventional optical disk such as a CD or DVD. In an optical pickup device including a combination of a laser having a relatively long wavelength and a low NA of an objective lens as described above, even a problem that can be almost ignored becomes more apparent.

One of the problems is a problem of axial chromatic aberration generated in an objective lens due to a minute fluctuation of an oscillation wavelength of a laser light source. The change in the refractive index of a general optical lens material due to a minute change in the wavelength increases as the wavelength becomes shorter. Therefore, the defocus amount of the focal point caused by the minute fluctuation of the wavelength increases. However, the depth of focus of the objective lens is k
・ As can be seen from λ / NA ² (k is a proportional constant, λ is the wavelength, and NA is the image-side numerical aperture of the objective lens), the shorter the oscillation wavelength of the light source used, the smaller the focal depth becomes. A slight amount of defocus is not allowed. Therefore, in an optical system using a short-wavelength light source such as a blue-violet semiconductor laser (oscillation wavelength of about 400 nm) and an objective lens having a high image-side numerical aperture, wavelength fluctuation due to output change such as a mode hop phenomenon of the semiconductor laser, It is important to correct longitudinal chromatic aberration in order to prevent deterioration of wavefront aberration due to high frequency superposition.

Another problem that becomes apparent in the combination of shortening the wavelength of the laser and increasing the NA of the objective lens is fluctuation of the spherical aberration of the optical system due to changes in temperature and humidity. That is, a plastic lens generally used in an optical pickup device is easily deformed due to a change in temperature or humidity, thereby changing a refractive index. Even in the case of spherical aberration fluctuation due to refractive index change, which was not a problem in the optical system used in the conventional pickup device, the amount cannot be ignored in the combination of shortening the wavelength of the laser light source and increasing the NA of the objective lens. This causes problems such as an increase in spot diameter.

However, when recording or reproducing information,
As described above, the light source wavelength and the NA of the objective lens are significantly different from the next-generation optical disk, which requires a combination of shortening the laser wavelength and increasing the NA of the objective lens, as described above. Further, in order to suppress the coma aberration which largely occurs due to the inclination of the disk surface from the plane perpendicular to the optical axis expected in the next-generation optical disk, it is effective to reduce the thickness of the transparent substrate. However, as a result, the thickness of the transparent substrate is greatly different from that of a conventional optical disk such as a CD. Therefore, by using at least a common objective lens, it is possible to reduce the spherical aberration of a compact optical pickup device to different optical information recording media including next-generation optical disks without greatly increasing the cost. The problem is whether to record or reproduce information.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an optical pickup device capable of effectively correcting a change in spherical aberration of an objective lens due to a change in temperature and humidity, an objective lens thereof, and a beam expander.

Another object of the present invention is to provide an optical pickup device capable of effectively correcting axial chromatic aberration caused by mode hop of a semiconductor laser and high frequency superposition, an objective lens thereof, and a beam expander.

Further, the present invention relates to a short wavelength laser and a high NA.
It is an object of the present invention to provide an optical pickup device including an objective lens and capable of recording or reproducing information on or from different optical information recording media.

[0010]

According to the present invention, there is provided an optical pickup device for collecting a light source and a light beam emitted from the light source on an information recording surface via a transparent substrate of an optical information recording medium. An optical pickup device having a condensing optical system including an objective lens and a photodetector for receiving reflected light from the optical information recording medium, wherein the objective lens is made of at least one plastic material. A temperature of -3 between the light source and the objective lens.
For an environmental change between 0 ° C. to + 85 ° C. and a humidity of 5% to 90%, the change is caused by a change in at least one of the shape and the refractive index of the objective lens and the oscillation wavelength of the light source.
Since the means for correcting the fluctuation of the spherical aberration is provided, even when the refractive index of the objective lens changes according to the temperature or humidity change of the environment in which the optical pickup device is used, or the oscillation of the light source Even when wavelength fluctuations occur, fluctuations in spherical aberration of the objective lens caused by the fluctuations can be effectively suppressed.

The distance between the light source and the objective lens is
The objective lens is included, so that even a diffractive surface provided on the surface of the objective lens can be a means for correcting the fluctuation of the spherical aberration of the present invention.

According to a second aspect of the present invention, there is provided an optical pickup device comprising:
A light condensing optical system including a light source having an oscillation wavelength λ, an objective lens for condensing a light beam emitted from the light source onto a data recording surface via a transparent substrate of the optical data recording medium, and the optical data recording medium An optical pickup device having a photodetector for receiving reflected light from the light source, wherein a means for correcting a variation in spherical aberration is provided between the light source and the objective lens, and a variation in the spherical aberration is provided. The correcting means is 0.2λr
Since the spherical aberration up to ms can be corrected to 0.07 λrms or less, for example, the spherical aberration of the objective lens caused by a change in the temperature or humidity of the environment in which the optical pickup device is used and / or a minute change in the oscillation wavelength of the light source. Fluctuations can be effectively suppressed.

An optical pickup device according to a third aspect of the present invention comprises:
The means for correcting the fluctuation of the spherical aberration is 0.5λrms.
It is preferable that the spherical aberration can be corrected to 0.07λrms or less.

According to a fourth aspect of the present invention, there is provided an optical pickup device comprising:
A light source, a condensing optical system including an objective lens for converging a light beam emitted from the light source onto an information recording surface via a transparent substrate of the optical information recording medium, and reflected light from the optical information recording medium An optical pickup device having a photodetector for receiving light, wherein a means is provided between the light source and the objective lens for correcting fluctuations in spherical aberration generated in the objective lens. Variations in the spherical aberration of the objective lens caused by changes in the temperature and humidity of the environment in which the pickup device is used and / or minute variations in the oscillation wavelength of the light source can be effectively suppressed.

The oscillation wavelength of the semiconductor laser is ± 10 nm
In optical systems using short-wavelength light sources and objective lenses with high image-side numerical apertures, the use of semiconductor lasers that deviate from the reference wavelength may cause performance degradation of the device due to the degree of individual variation. It may be necessary to select a semiconductor laser. 6. An optical pickup device according to claim 5, wherein a light-collecting optical system includes a light source and an objective lens for converging a light beam emitted from the light source onto an information recording surface via a transparent substrate of the optical information recording medium. And an optical detector having a photodetector for receiving reflected light from the optical information recording medium, wherein the optical pickup device has a small variation in the oscillation wavelength of the light source between the light source and the objective lens. Means for correcting the variation of the spherical aberration generated by the objective lens is provided, so that the variation of the spherical aberration of the objective lens caused when a semiconductor laser shifted from the reference wavelength is used is effectively suppressed. Therefore, it is not necessary to select the semiconductor laser.

An optical pickup device according to claim 6 is
A light source, a condensing optical system including an objective lens for converging a light beam emitted from the light source onto an information recording surface via a transparent substrate of the optical information recording medium, and reflected light from the optical information recording medium An optical pickup device having a photodetector for receiving light, wherein a variation in spherical aberration generated in the condensing optical system due to a change in temperature and humidity between the light source and the objective lens is corrected. Therefore, for example, a change in the spherical aberration of the objective lens caused by a change in temperature or humidity in an environment in which the optical pickup device is used can be effectively suppressed.

An optical pickup device according to claim 7 is
A light source, a condensing optical system including an objective lens for converging a light beam emitted from the light source onto an information recording surface via a transparent substrate of the optical information recording medium, and reflected light from the optical information recording medium An optical pickup device having a photodetector for receiving light, wherein the condensing optical system is disposed between the light source and the objective lens due to minute fluctuations in the oscillation wavelength of the light source and changes in temperature and humidity. Since the means for correcting the fluctuation of the spherical aberration generated in the optical pickup device is provided, for example, according to the temperature or humidity change of the environment in which the optical pickup device is used, and when using a semiconductor laser deviated from the reference wavelength as the light source The resulting fluctuation of the spherical aberration of the objective lens can be effectively suppressed.

An optical pickup device according to claim 8 is
The means for correcting the variation of the spherical aberration includes at least one positive lens and at least one negative lens, at least one of which is a movable element movable in the optical axis direction. . In the optical pickup device according to the ninth aspect, the means for correcting the fluctuation of the spherical aberration includes a positive lens group including one positive lens and having a positive refractive power, and a negative lens group including one negative lens. And at least one of the lens groups is a movable element that can move in the optical axis direction.

In the optical pickup device used for the short-wavelength light source, as described above, the fluctuation of the spherical aberration due to the fluctuation of the wavelength of the light source, the change of temperature and humidity, and the like is large. In particular, when an objective lens having a high image-side numerical aperture (high NA) or an objective lens made of a plastic material is used, the fluctuation is increased. Therefore, in an optical pickup device using a short-wavelength light source, it is particularly necessary to provide a means for correcting these fluctuations in spherical aberration. When the spherical aberration of the objective lens fluctuates due to a minute fluctuation of the oscillation wavelength of the light source or a change in temperature and humidity, the movable element of the means for correcting the fluctuation of the spherical aberration is moved by an appropriate amount, and the Variations in spherical aberration can be corrected by changing the degree of divergence of the light beam incident on the lens so that the spherical aberration of the wavefront formed on the information recording surface is minimized.

The optical pickup device according to the tenth and eleventh aspects is characterized in that the means for correcting the fluctuation of the spherical aberration satisfies the following expression. νdP> νdN (1) where νdP: average of Abbe numbers of d lines of all positive lenses including the positive lens νdN: average of Abbe numbers of d lines of all negative lenses including the negative lens

The above equation (1) relates to correction of longitudinal chromatic aberration. When the spherical aberration of the objective lens fluctuates due to a minute fluctuation of the oscillation wavelength of the light source or a change in temperature / humidity, a means for correcting the spherical aberration, for example, by using an optical element that can shift in the optical axis direction. When configured, the optical element can be moved by an appropriate amount to change the divergence of the light beam incident on the objective lens such that the spherical aberration of the objective lens is minimized. Longitudinal chromatic aberration of the objective lens, which is problematic when a short wavelength light source is used, can be corrected by configuring the means for correcting the fluctuation of the spherical aberration as described below.

By selecting the materials of the positive lens and the negative lens in the means for correcting the fluctuation of the spherical aberration so as to satisfy the above equation (1), chromatic aberration having a polarity opposite to the chromatic aberration generated by the objective lens is generated. Can be done. Therefore, since axial chromatic aberrations cancel each other, the wavefront transmitted through the means for correcting the fluctuation of the spherical aberration and the objective lens and focused on the optical information recording medium has a small axial chromatic aberration. It will be in the state that was done. If the diffractive surface is added to the objective lens and / or the means for correcting the fluctuation of the spherical aberration, and the diffractive lens is configured such that the back focus of the objective lens becomes shorter on the long wavelength side, the aberration can be more properly corrected. Becomes possible. In this case, the role of correcting the axial chromatic aberration can be shared between the means for correcting the variation of the spherical aberration and the diffractive surface, so that the means for correcting the variation of the spherical aberration can be shifted, for example, in the optical axis direction. When using elements, the stroke of the optical element can be small.

Further, the role of axial chromatic aberration correction is shared between the means for correcting the fluctuation of the spherical aberration and the diffraction surface, so that the power of the diffraction surface can be reduced. As a result, the diffraction lens having high diffraction efficiency can be easily manufactured. Therefore, without separately providing a means for correcting the fluctuation of the spherical aberration and a means for correcting the axial chromatic aberration, the spherical aberration of the entire optical system and the axial A compact optical pickup device in which the upper chromatic aberration is well corrected can be obtained.

The optical pickup device according to the twelfth and thirteenth aspects is characterized in that the νdP and the νdN satisfy the following equation. νdP> 55 (2) νdN <35 (3)

If the difference between the Abbe numbers of the positive lens and the negative lens is increased so as to satisfy the above equations (2) and (3), chromatic aberration of the opposite polarity to that of the objective lens can be generated more. Therefore, axial chromatic aberration of the optical pickup optical system can be corrected more favorably.

In the optical pickup device according to the present invention, when the means for correcting the fluctuation of the spherical aberration is constituted by a positive lens group including the positive lens and a negative lens group including the negative lens, The optical pickup device according to claim 15, wherein the means for correcting the fluctuation of the spherical aberration satisfies the following equation. Δd · │fP / fN│ / Δνd ≦ 0.05 (4) where Δd: recording or reproduction of information on one information recording surface of any one optical information recording medium on which information can be recorded or reproduced. FP: focal length of the positive lens group (mm) (however, when the positive lens group has a diffraction surface, the refraction power and the diffraction power are FN: focal length of the negative lens group (mm) (however, if the positive lens group has a diffractive surface, the total focal length of refraction power and diffraction power) Δνd: difference between the maximum value of the Abbe number of the positive lens and the minimum value of the Abbe number of the negative lens in the positive lens group and the negative lens group

The above equation (4) represents the correction amount of the axial chromatic aberration of the objective lens, the paraxial power of the means for correcting the fluctuation of the spherical aberration, and the movement amount of the movable element of the means for correcting the fluctuation of the spherical aberration. Regarding balance. Here, even if the value of Δνd is small, if the value of | fP / fN | is increased, the axial chromatic aberration of the objective lens can be corrected well, and the objective lens caused by the wavelength variation of the light source or the temperature / humidity variation If the means for correcting the variation of the spherical aberration is configured using an optical element that can be displaced in the optical axis direction, the stroke of the optical element can be reduced, but the effective diameter of the positive lens group is reduced. The negative lens group may become too large or the effective diameter of the negative lens group may become too small. Conversely, Δνd
If the value of | fP / fN | is small, it is possible to satisfactorily correct the axial chromatic aberration of the objective lens, but it is possible to correct the fluctuation of the spherical aberration necessary for correcting the spherical aberration. Since the moving amount of the movable element of the means for performing the operation becomes large, the size of the optical system may be increased. Therefore, by setting the value of Δd · | fP / fN | / Δνd so as to satisfy the above equation (5), it is possible to balance them.

The optical pickup device according to the present invention is capable of recording and / or reproducing information on at least two kinds of optical information recording media, and corrects the fluctuation of the spherical aberration. However, for at least two types of optical information recording media having different transparent substrate thicknesses, the divergence of a light beam incident on the objective lens is changed according to the respective transparent substrate thicknesses. Since the difference between the aberrations is corrected, and the fluctuation of the spherical aberration that occurs when recording or reproduction is performed on each optical information recording medium is corrected well, a good wavefront can always be formed on the information recording surface.

According to the optical pickup device of the present invention, information is recorded and / or recorded on an optical information recording medium in which a plurality of transparent substrates and information recording layers are laminated in order from the front side of the optical information recording medium. It is possible to reproduce, and the means for correcting the fluctuation of the spherical aberration, when condensing on each information recording layer, according to the information recording layer, the divergence of the light beam incident on the objective lens To compensate for differences in spherical aberration due to differences in thickness up to the information recording surface,
In addition, since the fluctuation of the spherical aberration that occurs when performing recording or reproduction on each information recording surface is satisfactorily corrected, a good wavefront can be formed on each information recording surface for each information recording surface. Thus, information can be recorded or reproduced satisfactorily even on an optical information recording medium having two or more information recording layers on one side of the optical information recording medium. For example, by moving the objective lens in the optical axis direction, it is possible to focus on one desired information recording surface, and at this time, the spherical aberration that fluctuates due to the difference in thickness up to the information recording surface is mainly tertiary. Since the spherical aberration is changed, the change of the spherical aberration can be satisfactorily corrected by moving the movable element of the means for correcting the change of the spherical aberration along the optical axis direction. Therefore, it is possible to record or reproduce information twice or more on one side of the optical information recording medium.

In the optical pickup device according to the present invention, when the transparent substrate thicknesses of the two types of optical information recording media are a and b (a <b), respectively,
When recording or reproducing information on or from the information recording surface of the optical information recording medium of the optical information recording medium, it is more negative than when recording or reproducing information on or from the information recording surface of the optical information recording medium having the transparent substrate thickness b. The distance between the lens and the positive lens is increased.

According to a twenty-second aspect of the present invention, in the optical pickup device, when the means for correcting the fluctuation of the spherical aberration includes a positive lens group including the positive lens and a negative lens group including the negative lens, The optical pickup device according to claim 23 satisfies the following expression. | FP / fN | ≧ 1.3 (5) where fP is the focal length of the positive lens group (however, when the positive lens group has a diffractive surface, the refracting power and the diffractive power are combined. FN: focal length of the negative lens group (when the negative lens group has a diffractive surface, the total focal length of refraction power and diffraction power combined)

The above equation (5) relates to the relationship of the paraxial power of the means for correcting the fluctuation of the spherical aberration. When the objective lens is corrected so that aberration is minimized based on a combination of transparent substrates having a specific thickness, when the thickness of the transparent substrate changes, the means for correcting the fluctuation of the spherical aberration is included. By moving the movable element, a light beam having a divergence that minimizes the spherical aberration of the objective lens with respect to its thickness must be incident on the objective lens. Therefore, by selecting the paraxial power of the means for correcting the fluctuation of the spherical aberration so as to satisfy the above equation (5), the stroke of the movable element can be small, and a compact optical system can be obtained as a whole. be able to.

In the optical pickup device described in claim 24, the means for correcting the variation of the spherical aberration has a shifting device for shifting the movable element along the optical axis in accordance with the variation of the spherical aberration. Features.

An optical pickup device according to a twenty-fifth aspect is characterized in that the movable element is formed of a material having a specific gravity of 2.0 or less. Thereby, the burden on the transfer device of the movable element can be reduced.

According to a twenty-sixth aspect, in the optical pickup device, at least one of the positive lens and the negative lens is formed of a plastic material. In particular, by forming the movable element of the spherical aberration correcting means from a plastic material, the load on the transfer device can be reduced, and high-speed tracking can be performed. Furthermore, if the components for providing the diffractive surface and the aspherical surface are formed from a plastic material, they can be easily added.

An optical pickup device according to a twenty-seventh aspect is characterized in that the movable element is formed of a plastic material. Thus, the weight of the optical system can be reduced, so that the burden on the moving device of the movable element can be reduced. Further, it becomes easy to add a diffraction structure.

An optical pickup device according to a twenty-eighth aspect is characterized in that at least one of the positive lens and the negative lens has an aspheric surface on at least one surface. And at least one surface of the movable element has an aspherical surface. By having the aspherical surface, the means for correcting the fluctuation of the spherical aberration can obtain an optical system with good performance by the aspherical aberration correcting action. In particular, by providing the movable element with an aspherical surface, it is possible to prevent the wavefront aberration from deteriorating at the time of eccentricity.

According to a thirtieth aspect of the present invention, in the optical pickup device, the means for correcting the fluctuation of the spherical aberration is made of a material having a saturated water absorption of 0.5% or less.

The optical pickup device according to claim 31, wherein the means for correcting the fluctuation of the spherical aberration has a material having an internal transmittance of 85% or more at a thickness of 3 mm with respect to the light having the oscillation wavelength of the light source. Characterized by being formed from

An optical pickup device according to a thirty-second aspect is characterized in that the means for correcting the fluctuation of the spherical aberration comprises the one positive lens and the one negative lens.

According to a thirty-fourth aspect of the present invention, in the optical pickup device, the means for correcting the fluctuation of the spherical aberration includes an optical element having a diffractive surface having a ring-like diffractive structure. Since the upper chromatic aberration can be effectively corrected, there is no need to newly provide an optical element or the like for correcting the axial chromatic aberration, thereby achieving low cost and space saving. The optical element having a diffractive surface includes one of the lens groups, and thus includes one of the positive lens group and the negative lens. In addition, it includes an optical element provided separately from the lenses.

An optical pickup device according to a thirty-fourth aspect is characterized in that the means for correcting the fluctuation of the spherical aberration has an element capable of changing the refractive index distribution. Such an element includes, but is not limited to, an element SE using liquid crystal, which will be described later with reference to FIGS.

An optical pickup device according to a thirty-fifth aspect of the present invention is a collection device including a light source and an objective lens for condensing a light beam emitted from the light source onto an information recording surface via a transparent substrate of an optical information recording medium. An optical pickup device having an optical optical system and a photodetector for receiving reflected light from the optical information recording medium, wherein a spherical surface generated by the objective lens is provided between the light source and the objective lens. Since the means for correcting the variation of aberration and the axial chromatic aberration generated in the objective lens is provided, the variation of the spherical aberration of the objective lens, which occurs when the oscillation wavelength of the semiconductor laser as the light source slightly varies, for example, It can be suppressed effectively.
Further, even when a change in the refractive index of the objective lens occurs in accordance with a change in environmental temperature or humidity, a change in spherical aberration of the objective lens due to the change can be effectively suppressed. Further, since axial chromatic aberration generated in the objective lens can be effectively corrected, even if an instantaneous oscillation wavelength jump (mode hop) occurs in which spherical aberration correcting means or focusing of the objective lens cannot follow, information is always obtained. A good wavefront can be formed on the recording surface.

The optical pickup device according to claim 36, wherein the means for correcting the fluctuation of the spherical aberration and the axial chromatic aberration includes at least one positive lens and at least one negative lens. One is characterized by being a movable element that can move in the optical axis direction. The optical pickup device according to claim 37, wherein the means for correcting the fluctuation of the spherical aberration and the axial chromatic aberration includes:
A positive lens group including positive lenses and having a positive refractive power;
A negative lens group including one negative lens and having a negative refractive power, wherein at least one of the lens groups is a movable element movable in the optical axis direction.

In the optical pickup device used for the short-wavelength light source, as described above, the fluctuation of the spherical aberration due to the fluctuation of the wavelength of the light source or the change of the temperature and humidity is large. In particular, when an objective lens having a high image-side numerical aperture (high NA) or an objective lens made of a plastic material is used, the fluctuation is increased. Therefore, in an optical pickup device using a short-wavelength light source, it is particularly necessary to provide a means for correcting these fluctuations in spherical aberration. If the spherical aberration of the objective lens fluctuates due to a minute fluctuation of the oscillation wavelength of the light source or a change in temperature and humidity, the movable element of the means for correcting the fluctuation of the spherical aberration and the axial chromatic aberration is appropriately adjusted. By changing the degree of divergence of the light beam incident on the objective lens such that the spherical aberration of the wavefront formed on the information recording surface is minimized, the fluctuation of the spherical aberration can be corrected.

The optical pickup device according to claims 38 and 39 is characterized in that the means for correcting the fluctuation of the spherical aberration and the axial chromatic aberration satisfies the above equation (1).

The above equation (1) relates to correction of longitudinal chromatic aberration. When the spherical aberration of the objective lens fluctuates due to a minute fluctuation of the oscillation wavelength of the light source or a change in temperature / humidity, a means for correcting the spherical aberration, for example, by using an optical element that can shift in the optical axis direction. When configured, the optical element can be moved by an appropriate amount to change the divergence of the light beam incident on the objective lens such that the spherical aberration of the objective lens is minimized. The axial chromatic aberration of the objective lens, which is problematic when using a light source with a short wavelength, can be corrected by configuring the means for correcting the fluctuation of the spherical aberration and the axial chromatic aberration as described below. .

By selecting the materials of the positive lens and the negative lens in the means for correcting the variation of the spherical aberration and the axial chromatic aberration so as to satisfy the above equation (1), the chromatic aberration generated by the objective lens is Chromatic aberration of opposite polarity can be generated. Therefore, since axial chromatic aberrations cancel each other out, the wavefront when focused on the optical information recording medium through the means for correcting the fluctuation of the spherical aberration and the axial chromatic aberration and the objective lens, This is a state where the axial chromatic aberration is suppressed to a small value. If a diffractive surface is added to the objective lens and / or a means for correcting the fluctuation of the spherical aberration and the axial chromatic aberration, and a diffractive lens that shortens the back focus of the objective lens on the long wavelength side, the aberration can be reduced. It is possible to perform better correction. In this case, the role of axial chromatic aberration correction can be shared by the means for correcting the variation of the spherical aberration and the axial chromatic aberration and the diffraction surface, so that the variation of the spherical aberration and the axial chromatic aberration are corrected. When the means is configured using, for example, an optical element that is movable in the optical axis direction,
The stroke of the optical element can be small.

Further, the role of axial chromatic aberration correction is shared between the diffraction surface and the means for correcting the fluctuation of the spherical aberration and the axial chromatic aberration, so that the power of the diffraction surface can be reduced. The interval between the diffraction zones becomes large, and it becomes easy to manufacture a diffraction lens having high diffraction efficiency. Therefore, without separately providing a means for correcting the fluctuation of the spherical aberration and a means for correcting the axial chromatic aberration, the spherical aberration of the entire optical system even when a wavelength change, a temperature and humidity change, etc. occur. And a compact optical pickup device in which axial chromatic aberration is well corrected.

In the optical pickup device according to claim 40, 41, the νdP and the νdN satisfy the above formulas (2) and (3).
Is satisfied.

If the difference between the Abbe numbers of the positive lens and the negative lens is increased so as to satisfy the above equations (2) and (3), chromatic aberration of the opposite polarity to that of the objective lens can be generated more. Therefore, axial chromatic aberration of the optical pickup optical system can be corrected more favorably.

The optical pickup device according to claim 42, wherein the means for correcting the fluctuation of the spherical aberration and the axial chromatic aberration includes a positive lens group including the positive lens and a negative lens group including the negative lens. 44. The optical pickup device according to claim 43, wherein, when configured, the optical pickup device according to claim 43, wherein the means for correcting the fluctuation of the spherical aberration and the axial chromatic aberration includes the expression (4). Is established.

The above equation (4) represents the correction amount of the axial chromatic aberration of the objective lens, the paraxial power of the means for correcting the variation of the spherical aberration and the axial chromatic aberration, and the variation of the spherical aberration and the axial aberration. It relates to the balance of the amount of movement of the movable element of the means for correcting upper chromatic aberration. Here, even if the value of Δνd is small, if the value of | fP / fN | is increased, the axial chromatic aberration of the objective lens can be corrected well, and the objective lens caused by the wavelength variation of the light source or the temperature / humidity variation When the means for correcting the variation of the spherical aberration and the axial chromatic aberration capable of correcting the variation of the spherical aberration is configured using an optical element displaceable in the optical axis direction, the stroke of the optical element is reduced. However, the effective diameter of the positive lens group may be too large, or the effective diameter of the negative lens group may be too small. Conversely, if the value of Δνd is increased, even if the value of | fP / fN |
Although the longitudinal chromatic aberration of the objective lens can be satisfactorily corrected, the moving amount of the movable element of the means for correcting the fluctuation of the spherical aberration and the longitudinal chromatic aberration necessary for correcting the spherical aberration increases. Therefore, the size of the optical system may be increased. Therefore, Δd · | fP / fN | / Δ
By making the value of νd satisfy the above equation (5), these can be balanced.

An optical pickup device according to claim 44, wherein the means for correcting the fluctuation of the spherical aberration and the axial chromatic aberration includes a positive lens group including the positive lens and a negative lens group including the negative lens. 46. The optical pickup device according to claim 45, wherein the means for correcting the fluctuation of the spherical aberration and the axial chromatic aberration satisfies the following equation. And Δd · │fP / fN│ ≦ 0.50 (6) where Δd: record or reproduce information on one information recording surface of any one optical information recording medium capable of recording or reproducing information. FP: focal length of the positive lens group (mm) (however, when the positive lens group has a diffractive surface, the refracting power and the diffracting power are combined) FN: focal length of the negative lens group (mm) (however, when the positive lens group has a diffractive surface, the total focal length of refraction power and diffraction power combined) Δνd : Difference between the maximum value of the Abbe number of the positive lens and the minimum value of the Abbe number of the negative lens in the positive lens group and the negative lens group

The above equation (6) represents the correction amount of the axial chromatic aberration of the objective lens, the paraxial power of the means for correcting the variation of the spherical aberration and the axial chromatic aberration, and the variation of the spherical aberration and the axial aberration. It relates to the balance of the amount of movement of the movable element of the means for correcting upper chromatic aberration. Refraction power as a refraction lens of the means for correcting the variation of the spherical aberration and the axial chromatic aberration,
The axial chromatic aberration of the objective lens can be corrected by appropriately combining the diffraction power of the diffraction surface added to the means for correcting the variation of the spherical aberration and the axial chromatic aberration. At this time, for example, means for correcting the fluctuation of the spherical aberration and the axial chromatic aberration, which also corrects the fluctuation of the spherical aberration of the objective lens due to the fluctuation of the oscillation wavelength of the light source or the change of temperature and humidity, in the optical axis direction. In the case of using a movable optical element, if the stroke of the optical element is too large, there arises a problem that spherical aberration cannot be satisfactorily corrected. Therefore, in the above equation (6), Δd ·
By setting the value of | fP / fN | to 0.50 or less, it is possible to maintain a good balance between the correction of the axial chromatic aberration and the correction of the spherical aberration of the objective lens.

According to the optical pickup device of the present invention, information can be recorded and / or reproduced on at least two kinds of optical information recording media, and the fluctuation of the spherical aberration and the on-axis information can be obtained. The means for correcting chromatic aberration changes the degree of divergence of a light beam incident on the objective lens according to the thickness of each transparent substrate for at least two types of optical information recording media having different transparent substrate thicknesses. It corrects the difference in spherical aberration due to the difference in substrate thickness and satisfactorily corrects the variation in spherical aberration that occurs when recording or reproducing on or from each optical information recording medium, so that a good wavefront is always present on the information recording surface. Can be formed.

According to another aspect of the present invention, there is provided an optical pickup device for recording and / or recording information on an optical information recording medium in which a plurality of transparent substrates and information recording layers are sequentially stacked from the front side of the optical information recording medium. Reproduction is possible, and means for correcting the fluctuation of the spherical aberration and the axial chromatic aberration impinges on the objective lens according to the information recording layer when condensing the information on each information recording layer. Changes the divergence of the luminous flux to correct the difference in spherical aberration due to the difference in thickness up to the information recording surface, and satisfactorily corrects the variation in spherical aberration that occurs when recording or reproducing on each information recording surface Therefore, a good wavefront can be formed on the information recording surface for each information recording surface. Thus, information can be recorded or reproduced satisfactorily even on an optical information recording medium having two or more information recording layers on one side of the optical information recording medium. For example,
By moving the objective lens in the direction of the optical axis, it is possible to focus on one desired information recording surface. At this time, the spherical aberration that fluctuates due to the difference in thickness up to the information recording surface is mainly tertiary spherical aberration. Therefore, by changing the movable element of the means for correcting the fluctuation of the spherical aberration and the axial chromatic aberration along the optical axis direction, the fluctuation of the spherical aberration can be satisfactorily corrected. Therefore, it is possible to record or reproduce information twice or more on one side of the optical information recording medium.

50. The optical pickup device according to claim 50, wherein when the transparent substrate thicknesses of said two types of optical information recording media are a and b (a <b), respectively, said transparent substrate thickness a
When recording or reproducing information on or from the information recording surface of the optical information recording medium of the optical information recording medium, it is more negative than when recording or reproducing information on or from the information recording surface of the optical information recording medium having the transparent substrate thickness b. The distance between the lens and the positive lens is increased.

The optical pickup device according to claim 52, wherein the means for correcting the fluctuation of the spherical aberration and the axial chromatic aberration is provided by a positive lens group including the positive lens and a negative lens group including the negative lens. When configured, the above formula (5) is satisfied, and the optical pickup device according to claim 53 is characterized by satisfying the above formula (5).

The above equation (5) relates to the relationship between the paraxial power of the means for correcting the fluctuation of the spherical aberration and the axial chromatic aberration. When the objective lens is corrected to minimize aberrations based on a combination of transparent substrates having a specific thickness, when the thickness of the transparent substrate changes, the variation of the spherical aberration and the axial chromatic aberration. By moving the movable element in the means for correcting the chromatic aberration, a luminous flux having a divergence that minimizes the spherical aberration of the objective lens with respect to its thickness must be incident on the objective lens. Therefore, the above equation (5)
By selecting the paraxial power of the means for correcting the fluctuation of the spherical aberration and the axial chromatic aberration so as to satisfy the following, the stroke of the movable element can be small, so that an overall compact optical system can be obtained. Can be.

In an optical pickup device according to a fifty-fourth aspect, the means for correcting the fluctuation of the spherical aberration and the axial chromatic aberration shifts the movable element along the optical axis according to the fluctuation of the spherical aberration. It is characterized by having a shifting device.

An optical pickup device according to a fifty-fifth aspect is characterized in that the movable element is formed of a material having a specific gravity of 2.0 or less. Thereby, the burden on the transfer device of the movable element can be reduced.

An optical pickup device according to claim 56, wherein at least one of the positive lens and the negative lens is formed of a plastic material. In particular, by forming the movable element of the means for correcting the fluctuation of the spherical aberration and the axial chromatic aberration from a plastic material, the load on the transfer device can be reduced, and high-speed tracking can be performed. Furthermore, if the components for providing the diffractive surface and the aspherical surface are formed from a plastic material, they can be easily added.

An optical pickup device according to a fifty-seventh aspect is characterized in that the movable element is formed of a plastic material. Thus, the weight of the optical system can be reduced, so that the burden on the moving device of the movable element can be reduced. Further, it becomes easy to add a diffraction structure.

The optical pickup device according to claim 58, wherein at least one of the positive lens and the negative lens has an aspheric surface on at least one surface. And at least one surface of the movable element has an aspherical surface. By having this aspherical surface, the means for correcting the fluctuation of the spherical aberration and the axial chromatic aberration can obtain an optical system having good performance by the aspherical aberration correcting action. In particular, by providing the movable element with an aspherical surface, it is possible to prevent the wavefront aberration from deteriorating at the time of eccentricity.

An optical pickup device according to claim 60, wherein the means for correcting the fluctuation of the spherical aberration and the axial chromatic aberration is formed of a material having a saturated water absorption of 0.5% or less. Features.

The optical pickup device according to claim 61, wherein the means for correcting the fluctuation of the spherical aberration and the axial chromatic aberration has a thickness of 3 mm with respect to the light having the oscillation wavelength of the light source.
Is formed of a material having an internal transmittance of 85% or more.

The optical pickup device according to claim 62, wherein the means for correcting the fluctuation of the spherical aberration and the axial chromatic aberration is constituted by the one positive lens and the one negative lens. It is characterized by.

The optical pickup device according to claim 63, wherein the means for correcting the fluctuation of the spherical aberration and the axial chromatic aberration includes an optical element having a diffraction surface having a ring-shaped diffraction structure. Since the axial chromatic aberration can be effectively corrected using the diffraction surface of the element, it is not necessary to newly provide an optical element for correcting the axial chromatic aberration, and low cost and space saving can be achieved. The optical element having a diffractive surface includes one of the lens groups, and thus includes one of the positive lens group and the negative lens. In addition, it includes an optical element provided separately from the lenses.

The optical pickup device described in Item 64 is characterized in that the means for correcting the fluctuation of the spherical aberration and the axial chromatic aberration includes an element capable of changing the refractive index distribution.

The optical pickup device according to claim 65, wherein the means for correcting the fluctuation of the spherical aberration and the axial chromatic aberration has a coupling lens having a function of correcting the axial chromatic aberration of the objective lens. It is characterized by the following.

The optical pickup device according to the 66th aspect is characterized in that it has an optical element having a diffraction surface having a ring-like diffraction structure.

The optical pickup device described in claim 67 is characterized in that the objective lens is the optical element (optical element having a diffraction surface having a ring-like diffraction structure).

The optical pickup device according to claim 68 is characterized in that the objective lens is a single objective lens having at least one aspherical surface and satisfies the following expression. 5.0 ≦ fD / f ≦ 40.0 (7) where, fD: the diffraction structure of the objective lens is Φb = b ₂ h ² +
b ₄ h ⁴ + b ₆ h ⁶ +... (where h is the height (mm) from the optical axis,
When b ₂ , b ₄ , b ₆ ,... are second-order, fourth-order, sixth-order,..., optical path difference function coefficients, fD = 1 / (− 2 ·
b ₂₎ is defined by the focal length at the oscillation wavelength of only by the light source the diffractive structure of the objective lens f: the objective a combination of the diffraction power by the diffractive structure of the the refractive power of the objective lens objective lens Focal length of the entire lens at the oscillation wavelength of the light source

The optical pickup device according to claim 68 relates to the correction of axial chromatic aberration of an objective lens used in an optical pickup device capable of satisfactorily correcting fluctuations in spherical aberration generated on each optical surface of a condensing optical system. . Oscillation wavelength 400n
When using a short-wavelength laser light source of about m and an objective lens having a high image-side numerical aperture of about 0.85 NA, correction of axial chromatic aberration generated in the objective lens can be an important problem for the above-mentioned reason. This problem is solved by providing the objective lens with a diffractive structure having a focal length satisfying the above equation (7). This diffractive structure has a wavelength characteristic such that when the oscillation wavelength of the laser light source fluctuates to a longer wavelength side, the back focus changes in a shorter direction. By appropriately selecting the power and the power so as to satisfy the above equation (7), it is possible to correct the axial chromatic aberration generated in the objective lens. When the value of fD / f is equal to or more than the lower limit of the above equation (7), the axial chromatic aberration of the objective lens is not excessively corrected, and when the value of fD / f is equal to or less than the upper limit, the axial chromatic aberration of the objective lens is not excessively corrected. . In addition, if the axial chromatic aberration of the objective lens is excessively corrected, the axial chromatic aberration generated in each optical element included in the focusing optical system can be exactly canceled by the objective lens, which is preferable.

The optical pickup device according to claim 69, wherein the diffractive structure has an n-th order diffracted light having a diffracted light amount larger than the diffracted light amount of any other order diffracted light among the diffracted light generated by the diffractive structure. (Where n is -1,
(An integer other than 0 and +1), and the n-order diffracted light is applied to the information recording surface of the optical information recording medium for recording and / or reproducing information on the optical information recording medium. Light is condensable.

An optical pickup device according to claim 69, in which recording or reproduction of information on or from an optical information recording medium is performed using second-order or higher-order diffracted light generated by a diffractive structure. The present invention relates to an optical system used for: When using the n-order diffracted light, +1 order or -1
Compared to the case where the next diffracted light is used, the ring interval (ring pitch) of the diffraction structure can be made about n times and the number of the rings is about 1 / n times. A lens mold can be easily manufactured, the processing time of the mold can be shortened, and a decrease in diffraction efficiency due to processing / manufacturing errors can be prevented.

An optical pickup device according to claim 70, further comprising an optical element having a diffractive surface having a ring-shaped diffractive structure, wherein the means for correcting the fluctuation of the spherical aberration includes an all positive lens including the positive lens. 72. The optical pickup device according to claim 71, wherein the Abbe number of each lens is 70.0 or less, or the Abbe number of all negative lenses including the negative lens is 40.0 or more. An optical element having a diffractive surface having a ring-shaped diffractive structure, wherein the means for correcting the fluctuation of the spherical aberration and the axial chromatic aberration has an Abbe number of 70% for each of the positive lenses including the positive lens. 0.0 or less, or the Abbe number of each negative lens including the negative lens is 4
0.0 or more.

An optical pickup device according to a seventy-fifth aspect relates to a preferable structure of a means for correcting a variation of the spherical aberration capable of correcting an axial chromatic aberration generated in an objective lens. The equipment is
The present invention relates to a preferable configuration of a means for correcting the fluctuation of the spherical aberration and the axial chromatic aberration capable of correcting the axial chromatic aberration generated in the objective lens. The Abbe number of the positive lens constituting the means for correcting the fluctuation of the spherical aberration or the means for correcting the fluctuation of the spherical aberration and the axial chromatic aberration is 70.0.
When the Abbe number of the negative lens is less than or equal to 40.0, axial chromatic aberration generated in the objective lens tends to be insufficiently corrected. In this case, a diffraction surface having a diffraction structure having a wavelength characteristic such that the back focus of the objective lens becomes short when the oscillation wavelength of the light source slightly fluctuates to the long wavelength side, means for correcting the fluctuation of the spherical aberration or By providing at least one of the constituent elements of the means for correcting the fluctuation of the spherical aberration and the axial chromatic aberration, the axial chromatic aberration of the objective lens can be satisfactorily corrected. Furthermore, by providing this diffraction surface with a spherical aberration characteristic such that the spherical aberration of the objective lens becomes insufficiently corrected when the oscillation wavelength of the light source slightly fluctuates to the longer wavelength side, the oscillation wavelength of the light source becomes longer. It is also possible to correct the spherical aberration caused by the minute fluctuation. When the Abbe number of the positive lens is 70.0 or less, the strength is excellent, the manufacturing is easy, and the environment resistance is good. On the other hand, when the Abbe number of the negative lens is 40.0 or more, the transparency to short-wavelength light is excellent. It is preferable that the Abbe number of both the positive lens and the negative lens is 40.0 or more and 70.0 or less.

In the optical pickup device described in claim 72, the means for correcting the fluctuation of the spherical aberration is provided.
Wherein the means for correcting the fluctuation of the spherical aberration and the axial chromatic aberration each have a paraxial power at an oscillation wavelength of the light source of P1, and a paraxial power at a wavelength shorter by 10 nm than the oscillation wavelength. Is P2 and paraxial power at a wavelength 10 nm longer than the oscillation wavelength is P3, and the following expression is satisfied. P2 <P1 <P3 (8)

Thus, the means for correcting the variation of the spherical aberration or the means for correcting the variation of the spherical aberration and the axial chromatic aberration can reduce the axial chromatic aberration generated by an optical element such as an objective lens or a coupling lens. It can have a role of correcting. That is, the means itself for correcting the fluctuation of the spherical aberration by the diffractive structure or the means itself for correcting the fluctuation of the spherical aberration and the axial chromatic aberration, excessively corrects the axial chromatic aberration, such as an objective lens and a coupling lens. By generating the axial chromatic aberration having the polarity opposite to that of the axial chromatic aberration generated by the optical element, the axial chromatic aberration generated by the optical element such as the objective lens and the coupling lens can be corrected.

An optical pickup device according to a seventy-fourth aspect is characterized in that the diffraction surface has a function of suppressing axial chromatic aberration generated in the objective lens with respect to a minute change in the oscillation wavelength of the light source. I do.

The optical pickup device according to claim 75, wherein the diffraction surface has a wavelength characteristic such that when the oscillation wavelength of the light source slightly fluctuates to the longer wavelength side, the back focus of the objective lens becomes shorter. It is characterized by the following. Thereby, axial chromatic aberration of the objective lens can be satisfactorily corrected. In particular, by providing the coupling lens and / or the objective lens with a diffractive surface to correct the axial chromatic aberration generated in the objective lens, the moment when the focusing of the spherical aberration changing means or the objective lens such as mode hop cannot follow. Thus, even when a significant wavelength change occurs, stable information recording or reproduction can be performed without increasing the spot diameter.

The optical pickup device according to claim 76, wherein the diffraction surface is oriented in such a manner that when the oscillation wavelength of the light source slightly fluctuates to the longer wavelength side, the spherical aberration of the objective lens is insufficiently corrected. It has a characteristic of changing spherical aberration. This makes it possible to satisfactorily correct spherical aberration when the oscillation wavelength of the light source slightly changes to the longer wavelength side.

An optical pickup device according to claim 77, wherein the light source comprises a light source having an oscillation wavelength λ1 and an oscillation wavelength λ2.
(Λ1 <λ2), and the condensing optical system converts the first light flux from the light source having the oscillation wavelength λ1 into a first optical information recording medium having a transparent substrate thickness t1. Of the objective lens required for recording or reproducing information within a predetermined numerical aperture on the image side of the objective lens.
Light can be collected in a state of 7λ1 rms or less, and the oscillation wavelength λ2
The second light flux emitted from the light source of the above is converted into a transparent substrate thickness t2.
With respect to the information recording surface of the second optical information recording medium (t1 ≦ t2), the wavefront aberration is 0.07λ2 rms or less within a predetermined numerical aperture on the image side of the objective lens required for recording or reproducing information. It can be focused.

For example, when recording or reproducing information on an optical information recording medium having a different transparent substrate thickness using a short wavelength light source such as a blue-violet semiconductor laser, one of the optical information recording media is If the objective lens is designed such that the spherical aberration correction is optimized, a large spherical aberration is generated in the other optical information recording medium when information is recorded or reproduced. More specifically, when the combination of the objective lens and the optical information recording medium having the transparent substrate thickness t1 is corrected so that the spherical aberration is minimized with respect to the incidence of the infinite parallel light beam, the transparent substrate at t2 (> t1) When recording or reproducing an optical information recording medium having a large thickness, an overcorrected spherical aberration occurs in the objective lens. Conversely, when recording or reproducing an optical information recording medium having a transparent substrate thickness of t2 '(<t1), insufficient correction spherical aberration occurs in the objective lens.

On the other hand, for example, a diffractive surface is added to the objective lens so that luminous fluxes having different wavelengths have a wavelength dependence so as to form good wave fronts on optical information recording media having different transparent substrate thicknesses. By using a lens, it is possible to satisfactorily correct spherical aberration when the thickness of the transparent substrate is different. As in the optical pickup device according to claim 77, the short-wavelength diffracted light forms a good wavefront on an optical information recording medium having a small transparent substrate thickness, and the long-wavelength diffracted light has a large transparent substrate thickness. It is preferable to form a good wavefront on the optical information recording medium.

More specifically, it is preferable that the diffractive surface has a spherical aberration characteristic such that the spherical aberration of the objective lens becomes insufficiently corrected when the wavelength of the light source slightly changes to the longer wavelength side. Further, divergence angle changing means for changing the divergence angle of the light beam is provided, and the divergence of the light beam incident on the objective lens is changed to the divergence corresponding to the object distance at which the spherical aberration is minimized, whereby the objective is changed. Spherical aberration of the lens can be better corrected. In particular, if the luminous flux of the optical information recording medium having the transparent substrate thickness of t2 at the time of the minimum spherical aberration is divergent light, it is easy to secure the working distance. Since the role of correcting spherical aberration degradation when the thickness of the transparent substrate is different can be shared between the divergence changing means and the diffractive surface, the amount of movement of the movable part of the divergence changing means can be small. Further, the role of the spherical aberration correction is shared by the divergence changing means and the diffraction surface, so that the power of the diffraction surface can be reduced, the interval between the diffraction zones becomes large, and the diffraction lens having high diffraction efficiency is obtained. Is easy to manufacture. In the above description, the objective lens is corrected so that the spherical aberration is minimized with respect to the light beam at infinity in combination with the transparent substrate thickness t1, but the divergent light beam from a finite distance or the image Either one may be corrected so as to minimize the spherical aberration with respect to the convergent light beam directed to the side object, and it goes without saying that the spherical aberration when the thickness of the transparent substrate is different can be corrected by the same method as described above.

An optical pickup device according to claim 78 is characterized in that it has an optical element having a diffraction surface having a ring-like diffraction structure.

The optical pickup device according to claim 79, wherein the diffraction surface of the optical element is configured to convert the first light beam emitted from the light source having the oscillation wavelength λ1 into a transparent substrate thickness t1.
Focusing on the information recording surface of the first optical information recording medium within a predetermined numerical aperture on the image side of the objective lens required for recording or reproducing information with a wavefront aberration of 0.07λ1 rms or less; The second light flux emitted from the light source having the oscillation wavelength λ2 (λ1 <λ2) is converted to a transparent substrate thickness t2 (t1 ≦ t
2) The light can be focused on the information recording surface of the second optical information recording medium with a wavefront aberration of 0.07λ2 rms or less within a predetermined numerical aperture on the image side of the objective lens required for recording or reproducing information. It is characterized by having such wavelength characteristics.
Specifically, the spherical aberration generated due to the difference in the thickness of the transparent substrate is calculated based on the difference between the oscillation wavelengths of two light sources used for recording and / or reproducing information on each optical information recording medium and the diffraction surface. The correction is performed by using the function of the diffraction structure provided in the above.

The optical pickup device according to claim 80, wherein an information recording surface of the first optical information recording medium is
A predetermined numerical aperture on the image side of the objective lens required for recording or reproducing information by the first light flux emitted from the light source of the oscillation wavelength λ1 is NA1, and the numerical aperture is on an information recording surface of the second information recording medium. On the other hand, a predetermined numerical aperture on the image side of the objective lens required for recording or reproducing information by the second light flux emitted from the light source of the oscillation wavelength λ2 is set to NA2.
When (NA1> NA2), the diffractive surface of the optical element transmits the second light flux emitted from the light source having the oscillation wavelength λ2 to the information recording surface of the second optical information recording medium. The light is condensed within the NA1 with a wavefront aberration of 0.07λ2 rms or more.

In particular, the spherical aberration is well corrected for the combination of the oscillation wavelength λ1, the transparent substrate thickness t1, and the image-side numerical aperture NA1. Transparent substrate thickness t2 and image-side numerical aperture NA
The spherical aberration up to the range of the image-side numerical aperture NA2 required for the combination with the numerical aperture 2 is corrected by the action of the diffraction structure, and the spherical aberration is increased in the range from the image-side numerical aperture NA2 to NA1 (flare). It is preferable to generate a large amount as a component). As a result, the second light flux having the oscillation wavelength λ2 is converted into the oscillation wavelength λ1 and the image-side numerical aperture N of the objective lens.
When the light is incident so as to pass through all of the inside of the stop determined by A1, the light flux having the image-side numerical aperture NA2 or more does not contribute to spot imaging, and the first optical information recording medium having the transparent substrate thickness t1 is not exposed. Since the spot diameter does not become too small on the information recording surface, it is possible to prevent the occurrence of erroneous signals and detection of unnecessary signals in the light receiving means of the optical pickup device, and furthermore, the oscillation wavelength of each light source and the corresponding image side. Since there is no need to provide a means for switching the aperture according to the combination with the numerical aperture, a simple optical pickup device can be obtained. In particular, the second light flux emitted from the light source having the oscillation wavelength λ2 is transmitted to the information recording surface of the second optical information recording medium in the NA1 at a wavefront aberration of 0.2λ2rm.
It is more preferable to condense light in a state of s or more.

The optical pickup device described in Item 81 is characterized in that the objective lens is the optical element (an optical element having a diffraction surface having a ring-shaped diffraction structure). An optical pickup device according to claim 82, wherein the objective lens is a single lens objective lens having at least one aspheric surface, and satisfies the following expression. 0.5 ≦ (f1 / νd) · fD1 ≦ 10.0 (9) where f1: the oscillation of the entire objective lens obtained by combining the refractive power of the objective lens and the diffraction power of the objective lens by the diffraction structure. Focal length (mm) at wavelength λ1 νd: Abbe number of d-line of the objective lens fD1: Φb = b ₂ h ²
+ B ₄ h ⁴ + b ₆ h ⁶ +... (Where h is the height (mm) from the optical axis and b ₂ , b ₄ , b ₆ ,...) … Is the second, fourth, sixth, etc.
..), FD = 1 / (− 2 ·
b ₂ ), the focal length at the oscillation wavelength λ1 due to only the diffractive structure of the objective lens (m
m)

An optical pickup device according to claim 83, wherein the objective lens is a single-lens objective lens having at least one aspheric surface, and satisfies the following expression. −25.0 ≦ (b ₂ /λ1)≦0.0 (10) where b ₂ : the diffraction structure of the objective lens is Φb = b ₂ h ² +
b ₄ h ⁴ + b ₆ h ⁶ +... (where h is the height (mm) from the optical axis,
b ₂ , b ₄ , b ₆ ,... are second-order, fourth-order, sixth-order,..., second-order optical path difference function coefficients, and λ1: the oscillation wavelength λ1 ( mm)

According to the optical pickup device of the present invention, axial chromatic aberration generated by an objective lens and optical surfaces of a condensing optical system can be applied to a plurality of optical information recording media having different transparent substrate thicknesses. The present invention relates to an optical pickup device capable of satisfactorily correcting fluctuations in spherical aberration that occurs, and in particular, in an optical pickup device that uses diffracted light of the same order for light beams of a plurality of light sources having different wavelengths, a diffraction structure is provided on an objective lens And the case where the axial chromatic aberration of the diffracted light of the same order is corrected by the action of the diffraction structure.

A short-wavelength light source (oscillation wavelength of about 500 nm or less) and a conventional image-side numerical aperture (for example, NA for a CD)
In the case of using an objective lens having an image-side numerical aperture higher than about 0.45 or about 0.6 for DVD, the thickness of the transparent substrate of the optical information recording medium is set to 0.1 in order to suppress the occurrence of coma. It is particularly effective to make the distance as small as 2 mm or less, but by satisfying the above equation (9), the axial chromatic aberration is excessively overcorrected for both the short-wavelength light source and the conventional long-wavelength light source, or excessively corrected. It can be corrected in a well-balanced manner without becoming too short, and has a wavelength characteristic that forms a good spot on each information recording surface for a plurality of optical information recording media having different transparent substrate thicknesses. By providing a diffraction structure on the objective lens, the conventional transparent substrate thickness (for example, 1.2 mm for CD, DVD
It is possible to record or reproduce information with a single optical pickup device (at least, an optical pickup device sharing an objective lens and its driving mechanism) even for an optical information recording medium having a large size of 0.6 mm. Become. In the above equation (9), the axial chromatic aberration is not excessively corrected for the light flux of the long wavelength light source of 600 nm to 800 nm above the lower limit of the left side, and the light flux of the short wavelength light source of 500 nm or less below the upper limit of the right side. On the other hand, the axial chromatic aberration can be prevented from being insufficiently corrected, which is preferable.

By satisfying the above expression (10),
The burden of aberration correction on the diffraction structure provided on the objective lens can be reduced, that is, by satisfying the above expression (10),
Since the diffraction structure provided in the objective lens can be made to have little role in correcting axial chromatic aberration generated in the condensing optical system, the ring spacing of the diffraction structure is large, the number of rings is small, and the diffraction efficiency is small. The objective lens can be high. Here, the case of b ₂ = 0 corresponds to the case where the axial chromatic aberration generated in the condensing optical system is not corrected by the diffraction structure provided in the objective lens, and −25.0 ≦ (b ₂ / λ1) < In the case of 0.0, a long wavelength light source (about 600 nm to 800 nm)
This corresponds to a case where the axial chromatic aberration is corrected with respect to the light beam of a short-wavelength light source (about 500 nm or less) so that the axial chromatic aberration of the light beam is not excessively corrected. The means for correcting the variation of the spherical aberration disposed between the objective lens and the light source for the undercorrected axial chromatic aberration.
The correction can be made by adopting the configuration described in 0, 11, 33, 38, 39, 63 or 65. In addition, when the axial chromatic aberration generated in the objective lens is corrected by the action of the diffractive structure, when the Abbe number of the material of the objective lens is νd, it is preferable that νd> 55.0 is satisfied. Can be kept small.

The optical pickup device described in Item 84 is characterized in that the diffractive surface has a function of correcting axial chromatic aberration generated in the objective lens with respect to minute fluctuations in the oscillation wavelength of the light source. I do.

The optical pickup device according to claim 85, wherein the diffraction surface has a wavelength characteristic such that when the oscillation wavelength of the light source slightly fluctuates to the longer wavelength side, the back focus of the objective lens becomes shorter. Therefore, it is possible to satisfactorily correct axial chromatic aberration which is a problem when a short wavelength light source is used.

The optical pickup device according to claim 86, wherein the diffraction surface is oriented in such a direction that the spherical aberration of the objective lens is insufficiently corrected when the oscillation wavelength of the light source slightly fluctuates to the longer wavelength side. It has a characteristic of changing spherical aberration. Accordingly, the role of spherical aberration correction can be shared between the means for correcting the fluctuation of the spherical aberration or the means for correcting the fluctuation of the spherical aberration and the axial chromatic aberration, and the diffractive surface. When the means for correcting the spherical aberration and the means for correcting the variation of the spherical aberration and the axial chromatic aberration are configured by using an optical element that can shift in the optical axis direction, the stroke amount of the optical element can be small. . Further, as described above, the role of spherical aberration correction is shared by the means for correcting the fluctuation of the spherical aberration or the means for correcting the fluctuation of the spherical aberration and the axial chromatic aberration, and the diffraction surface. Since the power of the diffraction surface can be suppressed and the interval between the diffraction zones can be increased, an optical element having high diffraction efficiency can be easily manufactured.

The optical pickup device according to claims 87 and 88, wherein the objective lens is configured to convert a plurality of light beams emitted from the light source by refraction on at least one surface in order from the optical axis side to the outer periphery. The optical device has at least a first portion, a second portion, and a third portion for splitting into a light beam, and the first portion and the third portion are formed of a first optical information recording medium having a transparent substrate thickness t1. A light flux from the light source can be collected so that information can be recorded or reproduced on the information recording surface, and the first portion and the second portion have a transparent substrate thickness t2 (t1 <t1 < The light beam from the light source can be focused so that information can be recorded or reproduced on the information recording surface of the second optical information recording medium at t2).

The optical pickup device according to claim 89, wherein at least one surface of the objective lens is provided with k (k ≧ 4) annular luminous fluxes (k ≧ 4) due to refraction.
From the optical axis side to the outside, first, second,.
.., A k-th light beam), and when recording and / or reproducing information on the first optical information recording medium, the first and the second are used. Kth
The spherical aberration component of the wavefront aberration of the first and k-th light beams at the best image plane position formed by the light beams is 0.05λ1 rms or less (light source wavelength of λ1), and the second to (k−
1) Among the light beams, at least two light beams have an apparent best image plane position formed at a position different from the best image surface position formed by the first and k-th light beams, respectively.
And at the best image plane position produced by the k-th light beam, the wavefront aberration of the light beam in each of the first to k-th light beams passing through the required numerical aperture for the first optical information recording medium is approximately miλ1 (mi Are integers, i = 1,2, ...
, K).

According to the optical pickup device described in Item 89, the thickness of the transparent substrate of the first optical information recording medium (first optical disk) and the thickness of the transparent substrate are determined by the plurality of divided surfaces divided by the annular step. In a substrate thickness difference between the transparent substrate thickness of the second optical information recording medium (second optical disk) and
Since the residual error is reduced, it is possible to appropriately record and / or reproduce information on a plurality of types of optical discs. FIG. 2 shows such an objective lens.
6 will be described later.

An optical pickup device according to claim 90, wherein the transparent substrate thickness t1 of the first optical information recording medium is:
The second optical information recording medium has a transparent substrate thickness t2 of 0.6 mm or more, and the oscillation wavelength λ2 is in a range of 600 nm to 800 nm.

In the optical pickup device according to the nineteenth aspect, among the spherical aberrations of the objective lens, the third-order spherical aberration component is SA1, and the sum of the fifth-, seventh-, and ninth-order spherical aberration components is SA2. At this time, the following expression is satisfied. | SA1 / SA2 |> 1.0 (11) where, SA1: a third-order spherical aberration component when the aberration function is expanded to a Zernike polynomial SA2: An aberration function is expanded to a Zernike polynomial Square root of the sum of squares of the fifth-order spherical aberration component, the seventh-order spherical aberration component, and the ninth-order spherical aberration component

The optical pickup device according to the nineteenth aspect relates to the balance of spherical aberration components of a substantial order of spherical aberration generated by an objective lens. In particular, in a single-lens objective lens having a high image-side numerical aperture, the amount of spherical aberration tends to increase due to a slight difference in the center thickness (on-axis thickness). When a lens is manufactured by molding, it is difficult to obtain a plurality of lenses with a runout having a center thickness of several μm or less. Since the spherical aberration component can be relatively easily corrected by the means for correcting the fluctuation of the spherical aberration or the means for correcting the fluctuation of the spherical aberration and the axial chromatic aberration,
The allowable range of the center thickness (in particular, the error from the design value) can be expanded.

The optical pickup device according to claim 92, wherein the stop for determining the numerical aperture of the objective lens is located closer to the side where the optical information recording medium is arranged than the surface vertex of the surface of the objective lens closest to the light source. It is characterized by being located.
Thereby, when the diverging light is incident on the objective lens, it is possible to suppress the light passage height of the surface of the objective lens closest to the light source, which is preferable for miniaturization of the objective lens or correction of aberration.

In the optical pickup device described in claim 93, since the objective lens is a single lens having at least one aspheric surface, spherical aberration or coma aberration can be effectively corrected, and the size and weight are small. A compact optical pickup device can be provided. In particular, it is more preferable that both surfaces are aspherical because spherical aberration and coma can be effectively corrected.

In the optical pickup device described in claim 94, since the light source has an oscillation wavelength of at least 500 nm or less, high-density information recording or high-density recording signal reproduction is possible. In addition, axial chromatic aberration that becomes a problem when a short wavelength light source having an oscillation wavelength of 500 nm or less is used is as follows.
In particular, correction can be made by adopting the configuration described in claims 10, 11, 33, 38, 39, 63 or 65.

An optical pickup device according to claim 95, wherein the image-side numerical aperture NA of the objective lens is at least 0.65 or more. The image-side numerical aperture of the objective lens is 0.65 or more (more preferably 0.75
The above) and making the optical information recording medium larger than in the prior art can achieve higher density and larger capacity of the optical information recording medium. Hereinafter, specific numerical values will be described. The spot diameter condensed on the optical information recording medium can be expressed by kλ / NA (k: proportional constant, λ: oscillation wavelength of the light source, NA: image-side numerical aperture of the objective lens). In a high-density optical pickup optical system using a laser and an objective lens having an image-side numerical aperture of 0.85, a low-density optical pickup optical system using a red semiconductor laser having an oscillation wavelength of 650 nm and an objective lens having an image-side numerical aperture of 0.65 is used. Spot diameter is about 1 /
It becomes 2. Here, the recording density on the optical information recording medium is:
Since it is proportional to the square of the reciprocal of the spot diameter ratio, the recording density of the high-density optical pickup optical system is four times that of the low-density optical pickup optical system.

The optical pickup device described in claim 96 is characterized in that the objective lens satisfies the following expression. 1.1 ≦ d1 / f ≦ 3.0 (12) where, d1: on-axis lens thickness (mm) f: focal length (mm) at the oscillation wavelength of the light source (however, a plurality of light sources having different oscillation wavelengths) If you have a light source, the focal length at the shortest oscillation wavelength,
If the objective lens has a diffractive surface, the total focal length including the refracting power and the diffracting power)

The above equation (12) relates to conditions for obtaining good image height characteristics. When trying to obtain a large image-side numerical aperture of 0.65 or more, if the value d1 / f is not less than the lower limit, good image height characteristics can be secured and shift sensitivity can be reduced.
In addition, the angle between the aspherical contact surface at the maximum effective diameter of the lens surface of the objective lens and the surface perpendicular to the optical axis can be reduced, making it easier to process the mold when molding the lens. become. On the other hand, when the value d1 / f is equal to or more than the upper limit, the center thickness (on-axis thickness) does not become too large, so that a large working distance can be secured. Also, since the occurrence of astigmatism can be kept small,
Good image height characteristics can be secured. From the above, the value d1 / f
More preferably satisfies the following expression. 1.2 ≦ d1 / f ≦ 2.3 (12 ′) Further, it is particularly desirable to satisfy the following expression. 1.4 ≦ d1 / f ≦ 1.8 (12 ″)

An optical pickup device according to claim 97, wherein the objective lens is formed of a plastic material. By making the objective lens made of plastic, weight reduction can be achieved, and the burden on the focusing mechanism can be reduced. Further, the objective lens can be mass-produced at low cost with stable accuracy. Further, when an aspherical surface or a diffractive surface is provided on the objective lens, they can be easily formed. In particular, it is preferable to manufacture by injection molding (including injection compression molding).

The optical pickup device according to claim 98, wherein the objective lens is formed of a material having a saturated water absorption of 0.5% or less. This is preferable because the change in the refractive index of the objective lens due to moisture absorption is reduced.

An optical pickup device according to claim 99, wherein said objective lens is formed of a material having an internal transmittance of 85% or more at a thickness of 3 mm with respect to light having an oscillation wavelength of said light source. It is characterized by. Thereby, energy saving can be achieved because a light source having a high light intensity is not required.

The objective lens according to claim 100 is applicable to the optical pickup device according to any one of claims 1 to 99.

The objective lens described in Item 101 is the objective lens used in the optical pickup device according to any one of Items 1 to 99.

An objective lens according to claim 102 is an optical pickup device capable of recording and / or reproducing information on at least two types of optical information recording media, comprising: a light source having an oscillation wavelength λ1; A light source having an oscillation wavelength λ2 (λ1 <λ2) different from the wavelength λ1 and a first light beam emitted from the light source having the oscillation wavelength λ1 are passed through a transparent substrate having a transparent substrate thickness t1 to a first optical information recording medium. And the second light flux emitted from the light source having the oscillation wavelength λ2 is transmitted to the second optical information recording medium through the transparent substrate having a transparent substrate thickness t2 (t1 ≦ t2). An objective lens for an optical pickup device, comprising: a condensing optical system including an objective lens for condensing light on an information recording surface; and a photodetector for receiving light reflected from the first and second optical information recording media. Must satisfy the following equation An objective lens according to claim. 1.1 ≦ d1 / f ≦ 3.0 (13) where, d1: on-axis lens thickness (mm) f: focal length (mm) at the oscillation wavelength λ1 (provided that the objective lens has a diffraction surface) In the case, the total focal length combining refraction power and diffraction power)

An objective lens according to claim 103, wherein the image-side numerical aperture NA is 0.75 or more.

An objective lens according to a tenth aspect is characterized in that the objective lens has a diffraction surface having a ring-like diffraction structure.

The objective lens according to claim 105, wherein the diffraction surface is configured to transfer the first light beam emitted from the light source having the oscillation wavelength λ1 to the information recording surface of the first optical information recording medium. A wavefront aberration of 0.07λ1 rms within a predetermined numerical aperture on the image side of the objective lens required for recording or reproducing information.
The second light flux emitted from the light source having the oscillation wavelength λ2 can be condensed in the following state, and the second light flux is transmitted to the information recording surface of the second information recording medium by the object necessary for recording or reproducing information. Wavefront aberration 0.07 within a predetermined numerical aperture on the image side of the lens
It is characterized by having a wavelength characteristic capable of condensing light in a state of λ2 rms or less.

The objective lens according to claim 106, wherein information is recorded or reproduced on the information recording surface of said first optical information recording medium by said first light flux emitted from said light source having said oscillation wavelength λ1. NA1 is a predetermined numerical aperture on the image side of the objective lens required for the above, and information of the second light flux emitted from the light source of the oscillation wavelength λ2 is transmitted to the information recording surface of the second information recording medium. The predetermined numerical aperture on the image side of the objective lens required for recording or reproduction is set to NA2 (NA1>
NA2), the diffraction surface has the oscillation wavelength λ2
The second light flux emitted from the light source is focused on the information recording surface of the second optical information recording medium in the NA1 with a wavefront aberration of 0.07λ2 rms or more.

The objective lens described in Item 107 is characterized in that the diffraction surface has a function of suppressing axial chromatic aberration with respect to minute fluctuations in the oscillation wavelength of the light source.

The objective lens according to claim 108, wherein the diffraction surface has a wavelength characteristic to shorten the back focus of the objective lens when the oscillation wavelength of the light source slightly fluctuates to a longer wavelength side. Features.

In the objective lens described in Item 109, the diffraction surface changes in a direction such that when the oscillation wavelength of the light source slightly fluctuates to the longer wavelength side, the spherical aberration of the objective lens becomes insufficiently corrected. It is characterized by having spherical aberration characteristics.

The objective lens described in Item 110 is a single lens having at least one aspheric surface, and satisfies the following expression. 0.5 ≦ (f1 / νd) · fD1 ≦ 10.0 (14) where f1: focal length (mm) at the oscillation wavelength λ1 obtained by combining refraction power and diffraction power by the diffraction structure. Νd: lens material Abbe number of d-line fD1: Φb = b ₂ h ² + b ₄ h ⁴ + b ₆ h ⁶
+ ……… (where h is the height (mm) from the optical axis and b ₂ , b ₄ , b
_6, ......... secondary, fourth, sixth, an optical path difference function coefficients of .........) time, fD = 1 / (- 2 · b 2) is defined by, the only by the diffractive structure Focal length at oscillation wavelength λ1 (mm)

By satisfying the above expression (14), axial chromatic aberration is not overcorrected or undercorrected with respect to both the short-wavelength light source and the conventional long-wavelength light source. Can be corrected. The above equation (1
4) In the range not less than the lower limit of the left side, 600 nm to 800 n
The axial chromatic aberration is not excessively corrected for the light flux of the long-wavelength light source m, and the axial chromatic aberration is not excessively undercorrected for the light flux of the short-wavelength light source of 500 nm or less below the upper limit on the right side. preferable. In addition, for a plurality of optical information recording media having different transparent substrate thicknesses, a diffraction structure having a wavelength characteristic such that a good spot is formed on each of the information recording surfaces is formed, so that the conventional transparent substrate thickness (for example, For a large optical information recording medium of 1.2 mm for CD and 0.6 mm for DVD, an optical information recording medium having a thin transparent substrate (for example, transparent) requiring a short wavelength light source and a high image-side numerical aperture. (Substrate thickness 0.2 mm or less), it is possible to obtain an objective lens that can also be used for recording or reproducing information.

The objective lens according to claim 111 is a single lens having at least one aspheric surface, and satisfies the following expression. −25.0 ≦ (b ₂ /λ1)≦0.0 (15) where b ₂ : the diffraction structure is Φb = b ₂ h ² + b ₄ h ⁴ + b ₆ h ⁶ +
……… expressed by the optical path difference function (where,
h is the height (mm) from the optical axis, and b ₂ , b ₄ , b ₆ ,
... Are the second-order, fourth-order, sixth-order,..., Second-order optical path difference function coefficients.) Λ1: The oscillation wavelength λ1 (mm)

Further, by satisfying the above expression (15),
The burden of aberration correction on the diffraction structure provided on the objective lens can be reduced, that is, by satisfying the above expression (15),
Since the diffraction structure provided in the objective lens can be made to have little role in correcting axial chromatic aberration generated in the condensing optical system, the ring spacing of the diffraction structure is large, the number of rings is small, and the diffraction efficiency is small. The objective lens can be high. Here, the case of b ₂ = 0 corresponds to the case where the axial chromatic aberration generated in the condensing optical system is not corrected by the diffraction structure provided in the objective lens, and −25.0 ≦ (b ₂ / λ1) < In the case of 0.0, a long wavelength light source (about 600 nm to 800 nm)
This corresponds to a case where the axial chromatic aberration is corrected with respect to the light beam of a short-wavelength light source (about 500 nm or less) so that the axial chromatic aberration of the light beam is not excessively corrected. The means for correcting the variation of the spherical aberration disposed between the objective lens and the light source for the undercorrected axial chromatic aberration.
The correction can be made by adopting the configuration described in 0, 11, 33, 38, 39, 63 or 65. In addition, when the axial chromatic aberration generated in the objective lens is corrected by the action of the diffractive structure, when the Abbe number of the material of the objective lens is νd, it is preferable that νd> 55.0 is satisfied. Can be kept small.

An objective lens according to claim 112, wherein the third-order spherical aberration components among the spherical aberrations are SA1, fifth-order, and seventh-order.
When the sum of the next and ninth order spherical aberration components is SA2, the following equation is satisfied. | SA1 / SA2 |> 1.0 (16) where SA1: a third-order spherical aberration component when the aberration function is expanded to a Zernike polynomial SA2: An aberration function is expanded to a Zernike polynomial Square root of the sum of squares of the fifth-order spherical aberration component, the seventh-order spherical aberration component, and the ninth-order spherical aberration component

The balance of the spherical aberration components of the substantial order of the spherical aberration generated by the objective lens. In particular,
In a single-lens objective lens having a high image-side numerical aperture, the amount of spherical aberration tends to increase due to a slight difference in the center thickness (axial thickness). Therefore, the allowable range of the center thickness required for the objective lens is very large. When a lens is manufactured by molding, it is difficult to obtain a plurality of lenses with a center thickness of several μm or less. However, when the above equation (11) is satisfied, the lens is generated by the objective lens. The balance of the spherical aberration component of the substantial order of the spherical aberration can be improved, and the allowable range of the center thickness required for the objective lens (in particular, the error from the design value) can be expanded.

The objective lens according to claim 113, wherein at least one surface divides a light beam emitted from the light source by a refraction action into a plurality of light beams in order from the optical axis side to the outer periphery thereof. , A second part, and a third part, wherein the first part and the third part record or reproduce information on or from an information recording surface of the first optical information recording medium. The light beam from the light source having the oscillation wavelength λ1 can be collected so that the first
And the second portion are capable of condensing a light beam from the light source having the oscillation wavelength λ2 so that information can be recorded or reproduced on the information recording surface of the second optical information recording medium. It is characterized by being.

In the objective lens described in Item 114, k incident light beams (k ≧
4) Forming an annular step portion which is divided into annular light fluxes (here, in order from the optical axis side to the outside thereof, first, second,..., K-th light fluxes). When information is recorded and / or reproduced on the first optical information recording medium, the wavefront aberration of the first and k-th light beams at the best image plane position formed by the first and k-th light beams Is not more than 0.05λ1 rms (light source wavelength of λ1), and at least two of the second to (k−1) th light fluxes are the best formed by the first and kth light fluxes, respectively. An apparent best image plane position is formed at a position different from the image plane position, and passes through the required numerical aperture for the first optical information recording medium at the best image plane position created by the first and k-th light beams. Wavefront collection of light rays in each of the first to k-th light beams Approximately miλ1 (mi-number is an integer, i = 1,2, ······, k), characterized in that a.

The objective lens according to claim 115 is characterized in that it is formed of a plastic material.

An objective lens according to claim 116 is characterized in that the objective lens is formed of a material having a saturated water absorption of 0.5% or less.

An objective lens according to claim 117 is characterized in that the objective lens is formed of a material having an internal transmittance of 85% or more at a thickness of 3 mm with respect to the oscillation wavelength of the light source.

The objective lens according to claim 118 is characterized in that at least one surface is an aspherical single lens.

The objective lens according to claim 119 is applicable to the optical pickup device according to any one of claims 1 to 99.

[0139] The beam expander according to claim 120 includes at least one positive lens and at least one negative lens, at least one of which is a movable element that can move along the optical axis direction. The Abbe number of all positive lenses including the positive lens is 70.0 or less, or the Abbe number of all negative lenses including the negative lens is 40.0 or more, and at least one surface has an annular diffraction structure. Characterized by having a diffraction surface having

When the Abbe number of the positive lens constituting the beam expander is 70.0 or less or the Abbe number of the negative lens is 40.0 or more, other optical elements (especially, preferably applied to an optical pickup device) The axial chromatic aberration generated by the objective lens tends to be insufficiently corrected, but by providing the diffraction surface, the axial chromatic aberration can be satisfactorily corrected. In particular, by providing at least one diffraction surface having a diffraction structure having a wavelength characteristic such that the back focus of the objective lens becomes short when the oscillation wavelength of the incident light source slightly fluctuates to the long wavelength side,
It is possible to satisfactorily correct axial chromatic aberration of the objective lens. Furthermore, by providing this diffraction surface with a spherical aberration characteristic such that the spherical aberration of the objective lens becomes insufficiently corrected when the oscillation wavelength of the light source slightly fluctuates to the longer wavelength side, the oscillation wavelength of the light source becomes longer. It is also possible to correct the spherical aberration caused by the minute fluctuation. When the Abbe number of the positive lens is 70.0 or less, the strength is excellent, the manufacturing is easy, and the environment resistance is good. On the other hand, the Abbe number of the negative lens is 4
When it is 0.0 or more, it is excellent in transparency to light having a short wavelength. It is preferable that the Abbe number of both the positive lens and the negative lens is 40.0 or more and 70.0 or less.

The beam expander according to claim 121, wherein the paraxial power at the oscillation wavelength of the light source for outputting the incident light beam is P1, the paraxial power at a wavelength 10 nm shorter than the oscillation wavelength is P2, and the paraxial power at the oscillation wavelength is P2. When the paraxial power at a wavelength longer by 10 nm is P3, the following formula is satisfied. P2 <P1 <P3 (17)

Thus, the beam expander can have a role of correcting axial chromatic aberration generated by an optical element such as an objective lens or a coupling lens. That is, the beam expander itself excessively corrects axial chromatic aberration by the diffraction structure, and generates axial chromatic aberration having a polarity opposite to that of axial chromatic aberration generated by an optical element such as an objective lens or a coupling lens. It is possible to correct axial chromatic aberration generated in an optical element such as a lens or a coupling lens.

A beam expander according to claim 122, wherein said diffraction surface has an axial chromatic aberration generated by a condenser lens disposed on the exit side with respect to a minute fluctuation of an oscillation wavelength of a light source that outputs a light beam to be incident. Characterized by having a function of suppressing

A beam expander according to claim 123, wherein the diffractive surface of the condenser lens disposed on the exit side when the oscillation wavelength of the light source for outputting the incident light beam slightly fluctuates to the longer wavelength side. It is characterized by having wavelength characteristics such that the focus becomes short. Thereby, axial chromatic aberration of an optical element such as an objective lens can be satisfactorily corrected.

A beam expander according to claim 124, wherein the diffractive surface of the condenser lens arranged on the exit side when the oscillation wavelength of the light source for outputting the incident light beam slightly fluctuates to the longer wavelength side. It is characterized by having a spherical aberration characteristic that changes in a direction in which the aberration is undercorrected.
This makes it possible to satisfactorily correct spherical aberration when the oscillation wavelength of the light source that outputs the input light beam slightly fluctuates to the longer wavelength side.

[0146] The beam expander according to claim 125 is characterized in that the movable element is formed of a material having a specific gravity of 2.0 or less. Thereby, the burden on the transfer device of the movable element can be reduced.

[0147] The beam expander according to claim 126 is characterized in that the movable element is formed of a plastic material. Thereby, the load on the transfer device can be reduced, and the movable element can be moved at high speed in the optical axis direction. Furthermore, if the components for providing the diffractive surface and the aspherical surface are formed from a plastic material, they can be easily added.

The beam expander according to claim 127 is characterized in that at least one surface of the movable element has an aspheric surface.

[0149] The beam expander according to claim 128 is characterized in that the movable element is formed of a material having a saturated water absorption of 0.5% or less.

The beam expander according to claim 129, wherein the movable element is formed of a material having an internal transmittance of 85% or more at a thickness of 3 mm with respect to light having an oscillation wavelength of a light source to be incident. It is characterized by.

The beam expander according to claim 130 is characterized by being formed from a plastic material.

The beam expander according to claim 131 has at least one aspherical surface.

The beam expander according to claim 132 is characterized in that it is made of a material having a saturated water absorption of 0.5% or less.

The beam expander according to claim 133 has a thickness of 3 with respect to the light of the oscillation wavelength of the light source to be incident.
It is made of a material having an internal transmittance of 85% or more in mm.

A beam expander according to claim 134 is applicable to the optical pickup device according to any one of claims 8 to 33 and 36 to 63.

As used herein, the term “diffractive surface” refers to a form (or surface) in which a relief is provided on the surface of an optical element, for example, the surface of a lens to change the angle of a light beam by diffraction. In other words, when there is a region where diffraction occurs and a region where diffraction does not occur on one optical surface, it refers to a region where diffraction occurs. As the shape of the relief, for example, on the surface of the optical element, it is formed as a substantially concentric annular zone centered on the optical axis, and when viewed in cross section on a plane including the optical axis, each annular zone is shaped like a saw tooth Are known, but include such shapes. In particular, such a saw-tooth ring structure is preferable.

In the present specification, an objective lens is, in a narrow sense, a collection arranged to face the optical information recording medium closest to the optical information recording medium when the optical information recording medium is loaded in the optical pickup device. Refers to a lens that has a light effect,
In a broad sense, it refers to a lens group that can be operated at least in the optical axis direction by an actuator together with the lens.

In this specification, the condensing optical system includes at least an objective lens, is disposed between the light source and the objective lens, and is a coupling lens for converting an incident light beam into a substantially parallel light beam. (Including a collimator that converts the incident divergent light beam into a parallel light beam). However, it is an aggregate of at least optical elements functioning integrally, such as a beam expander to be described later, and an aggregate in which some optical elements constituting the aggregate can be displaced along the optical axis direction, and Here, some optical elements of the aggregate are not included in the condensing optical system. Note that the coupling lens may be composed of a plurality of lenses, or the lenses may be separated from each other and another optical element may be interposed therebetween.

In the present specification, a beam expander is capable of displacing at least one optical element such as a lens along the optical axis direction, whereby the divergence angle (including the divergence function and the convergence function) of the emitted light beam is obtained. Is variable, and
An aggregate of optical elements such as lenses that can emit substantially parallel light beams when substantially parallel light beams are incident (optical element groups such as lens groups)
Shall be referred to. It is preferable that a plurality of optical elements such as those lenses are integrated, and if at least one optical element such as a lens is configured to be movable at least along the optical axis direction, the transition is actually performed. Driving means such as a shifting device to perform may not be included as a beam expander.

In the present specification, the means for correcting the fluctuation of the spherical aberration and the axial chromatic aberration is a single means for correcting the fluctuation of the spherical aberration and the means for correcting the axial chromatic aberration. One optical element or an assembly thereof (for example, a beam expander) means that the configuration has both two correction functions. For example, a positive lens and a negative lens having a specific Abbe number A configured beam expander, a beam expander having a surface having a diffractive structure, and the like are included. In the present specification, in the invention relating to the optical pickup device, unless otherwise specified, the focal length is a focal length of a light source that emits light having the shortest oscillation wavelength among the light sources used, with respect to the oscillation wavelength. Shall be referred to.

In this specification, the minute fluctuation of the oscillation wavelength of the light source means a wavelength fluctuation within a range of ± 10 nm with respect to the oscillation wavelength of the light source. In the present specification, “correcting various aberrations” (satisfactorily) means “diffraction-limited performance” when wavefront aberration is obtained.
It is preferably 7λrms or less (here, λ is the oscillation wavelength of the light source used), and more preferably 0.05λrms or less in consideration of the mechanical accuracy of the device. With these, for various optical information recording media,
An appropriate spot size can be obtained for each.

In this specification, examples of the optical information recording medium (optical disc) include CD-R, CD-RW, and CD-Vide.
o, Various CDs such as CD-ROM, DVD-ROM, DVD-RAM, DVD-
Various DVDs such as R, DVD-RW, DVD-Video and the like, and current optical information recording media in the form of disks such as MDs and next-generation optical information recording media are also included. In addition, the transparent substrate used in this specification includes a case where the thickness is 0 mm, that is, the case where no transparent substrate exists.

In this specification, recording and reproducing information means recording information on the information recording surface of the optical information recording medium as described above, and reproducing information recorded on the information recording surface. Say. The optical pickup device of the present invention includes:
It may be used for performing only recording or reproduction, or may be used for performing both recording and reproduction. Further, it may be used for performing recording on a certain optical information recording medium and performing reproduction on another optical information recording medium,
Performs recording or reproduction on a certain optical information recording medium,
The other optical information recording medium may be used for recording and reproducing. Note that the reproduction here includes simply reading information.

The optical pickup device of the present invention can be mounted on a recording and / or reproducing apparatus for audio and / or images, such as various players or drives, or AV equipment, personal computers and other information terminals incorporating them. Can be.

[0165]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The aspherical surface used in the present embodiment is represented by the following [Equation 1]. Here, x is the axis in the optical axis direction, h is the axis perpendicular to the optical axis, and the traveling direction of light is positive, r is the paraxial radius of curvature, κ is the conic coefficient, and A _2i is the aspheric coefficient.

(Equation 1)

The diffractive surface used in the present embodiment is represented by [Equation 2] as an optical path difference function.

(Equation 2)

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic configuration diagram of an optical pickup device according to the present embodiment. FIG.
, A first light source 11 for recording and / or reproducing on the first optical information recording medium 23 and a first light source 11 for recording and / or reproducing on the second optical information recording medium 24
Coupling lenses 21 and 22 for converting a divergent angle of a divergent light beam emitted from each light source into a desired divergence angle, and a second light source 12 having a different wavelength from the light source 11, and light beams from the respective light sources. A beam splitter 62, which is an optical path combining means for causing the light beam to travel in substantially the same direction, an objective lens 3 for condensing the light beam from the beam splitter 62 on the information recording surface 5 of the optical information recording medium, and an optical information recording medium. And light detectors 41 and 42 for receiving the reflected light of. In the figure, 8 is a stop, 9 is a cylindrical lens, 7
1, 72 are quarter-wave plates, 15 is a coupling lens for reducing the degree of divergence of the divergent light beam from the light source 11, 1
Reference numeral 6 denotes a concave lens, and reference numeral 17 denotes a hologram for separating a reflected light beam.

Further, in the present embodiment, as means for correcting the fluctuation of the spherical aberration of the objective lens 3 and means for changing the divergence, the negative lens 5, the positive lens 4, the actuator 7 (Hereinafter,
Spherical aberration correcting means and divergence changing means). The actuator 7 functions as a transfer device that changes the divergence angle of the light beam by moving the negative lens 5 as an optical element in the optical axis direction. Further, in connection with the present embodiment, in Examples 1 to 14 showing specific partial optical systems,
An example of a so-called beam expander including the movable negative lens 5 and the positive lens 4 is sometimes referred to as a spherical aberration correcting unit. Reference numeral 6 denotes an actuator for driving the objective lens 3 in the optical axis direction for focusing. The first light source 11 has a wavelength λ1 = 405.
and the second light source 12 emits a laser beam having a wavelength λ2 = 6.
It is assumed that a laser beam of 55 nm can be emitted.

In the embodiments described below, the first embodiment,
2, 11 and 12 provide a diffraction surface on the objective lens 3 to correct axial chromatic aberration. In Examples 3 to 5, the negative lens 5 and the positive lens 4 use specific materials to reduce axial chromatic aberration. In Examples 6 to 8, 13 and 14, at least one of the negative lens 5 and the positive lens 4 is provided with a diffractive surface and the objective lens 3
In the ninth and tenth embodiments, the axial chromatic aberration of the objective lens 3 is reduced by the synergistic effect of the specific materials of the negative lens 5 and the positive lens 4 and the diffractive surface provided on the positive lens 4. Has been corrected. The fourth, fifth, and twelfth embodiments are examples in which information is recorded or reproduced on different optical information recording media using the same optical system. In the following examples of the objective lens, a plastic material having a water absorption of 0.01% or less, a transmittance of 90.5% by a light beam having a light source wavelength of 400 nm, and a transmittance of 92% by a light beam having a light source wavelength of 700 nm is 92%. Formed. Further, in the following examples, in the example using only the first light source 11 in the present embodiment shown in FIG. 1, the drawing of the specific embodiment is omitted, but generally in the pickup device of FIG. 1. For example, an embodiment in which the second light source 12, the coupling lens 22, the beam splitter 62, the photodetector 42, the quarter-wave plate 72, and the hologram 17 are removed can be adopted. Hereinafter, each embodiment will be described.

(Example 1) Table 1 shows that
The data on the optical system including the negative lens 5, the positive lens 4, and the objective lens 3 is shown. Incidentally, in the lens data shown below, a power of 10 (for example, 2.5 × 1
0 ⁻³ ) is represented using E (for example, 2.5 × E−3). In addition, primary light due to diffraction on a diffraction surface represented by a rotationally symmetric polynomial means light whose angle of light changes in a direction converging after diffraction.

[Table 1]

FIG. 2 is an optical system configuration diagram of the negative lens 5, the positive lens 4, and the objective lens 3 according to the first embodiment. FIG.
4 is a diagram of spherical aberration applied to the objective lens 3. FIG. Example 1
In, information is recorded or reproduced by a combination of the first light source 11 having a wavelength of 405 nm and the image-side numerical aperture NA of the objective lens 3 of 0.85. In this embodiment, the negative lens 5 of the means for correcting the fluctuation of the spherical aberration is used.
And νdN = 23.
8, a material having νdP = 81.6 is selected, and a diffractive surface is provided on the surface of the objective lens 3 on the light source side.
Is corrected for axial chromatic aberration. In this embodiment, fN = −8.13 (mm) and fP = 9.4.
8 (mm), f = 1.765 (mm), fD = 7
1.483 (mm).

In this embodiment, the correction of the minute fluctuation of the oscillation wavelength of the light source (hereinafter, also simply referred to as wavelength fluctuation) or the fluctuation of the spherical aberration caused by the temperature change can be performed as follows. In the case of the present embodiment, when the wavelength increases or when the temperature rises, the objective lens 3 generates overcorrected spherical aberration. In such a case, if the generated spherical aberration is moved along the optical axis by the actuator 7 to reduce the distance between the negative lens 5 and the positive lens 4, insufficiently corrected spherical aberration can be generated. . If the negative lens 5 is moved by an appropriate amount, the overcorrected spherical aberration can be canceled, and the spherical aberration of the entire optical system becomes good as is clear from Table 2 showing the result of the correction of the spherical aberration.

[Table 2]

(Example 2) Table 3 shows that
The data on the optical system including the negative lens 5, the positive lens 4, and the objective lens 3 is shown.

[Table 3]

FIG. 4 is an optical system configuration diagram of the negative lens 5, the positive lens 4, and the objective lens 3 according to the second embodiment. FIG.
4 is a diagram of spherical aberration applied to the objective lens 3. FIG. Example 2
In, information is recorded or reproduced by a combination of the first light source 11 having a wavelength of 405 nm and the image-side numerical aperture NA of the objective lens 3 of 0.85. In the second embodiment,
As the material of the negative lens 5 and the positive lens 4 of the means for correcting the fluctuation of the spherical aberration, νdN = 30.0 and νdN, respectively.
By selecting a material of dP = 56.5 and providing a diffraction surface on the surface of the objective lens 3 on the light source side, axial chromatic aberration generated in the objective lens 3 is corrected. In this embodiment, fN = −4.75 (mm) and fP = 6.47 (m)
m), f = 1.765 (mm), fD = 71.4
83 (mm).

The correction of the variation of the spherical aberration caused by the wavelength variation or the temperature variation in the present embodiment is the same as that of the first embodiment, and the explanation is omitted. Table 4 showing correction results of spherical aberration
As is clear from FIG. 7, the spherical aberration at the time of wavelength change or temperature change is good. Further, as a means for correcting the fluctuation of the objective lens 3 and the spherical aberration, by using a plastic material for the negative lens 5 and the positive lens 4,
The weight of the optical system and the load on the movable mechanism are reduced.

[Table 4]

(Example 3) Table 5 shows that
The data on the optical system including the negative lens 5, the positive lens 4, and the objective lens 3 is shown.

[Table 5]

FIG. 6 is an optical system configuration diagram of the negative lens 5, the positive lens 4, and the objective lens 3 according to the third embodiment. FIG.
4 is a diagram of spherical aberration applied to the objective lens 3. FIG. Example 3
In, information is recorded or reproduced by a combination of the first light source 11 having a wavelength of 405 nm and the image-side numerical aperture NA of the objective lens 3 of 0.85. In the third embodiment, longitudinal chromatic aberration is corrected by selecting materials of νdN = 23.8 and νdP = 81.6 as materials of the negative lens 5 and the positive lens 4, respectively. In this embodiment, fN = −9.27 (mm) and fP = 11.08.
(Mm), and f = 1.765 (mm).

The correction of the spherical aberration at the time of a wavelength change or a temperature change in the present embodiment is the same as that of the first embodiment, and the description is omitted. As is clear from Table 6 showing the correction results of the spherical aberration, the spherical aberration at the time of the wavelength change or the temperature change is excellent. Further, by using a plastic material for the objective lens 3, the weight of the optical system is reduced and the burden on the movable mechanism is reduced.

[Table 6]

(Example 4) Table 7 shows that
The data on the optical system including the negative lens 5, the positive lens 4, and the objective lens 3 is shown.

[Table 7]

FIGS. 8 and 9 are optical system diagrams of the negative lens 5, the positive lens 4, and the objective lens 3 according to the fourth embodiment. 10 and 11 are diagrams of spherical aberration applied to the objective lens 3 when recording or reproducing information on different optical information recording media, respectively. In the fourth embodiment, using the same optical system, the first light source 1 having a wavelength of 405 nm is used.
Information is recorded or reproduced by a combination of No. 1 and an optical information recording medium having a transparent substrate thickness of 0.1 mm, or a combination of the second light source 11 having a wavelength of 655 nm and an optical information recording medium having a transparent substrate thickness of 0.6 mm. It is an example of an optical pickup device. In Example 4, the materials of the negative lens 5 and the positive lens 4 were νdN = 30.0 and νdP = 5, respectively.
By selecting the material of 6.5, longitudinal chromatic aberration is corrected. In this embodiment, fN = −3.82 (m
m), fP = 6.85 (mm), and f1 = 1.76
5 (mm) and fD1 = 50000000.02 (mm). The focal length of the objective lens at the oscillation wavelength λ2 = 655 nm is f2 = 1.804.

In the fourth embodiment, the fluctuation of the spherical aberration caused by the difference in the thickness of the transparent substrate in different optical information recording media is reduced by one negative lens 5 and one positive lens 4 in order from the light source side. The divergence angle changing means (corresponding to the means for correcting the fluctuation of the spherical aberration of the present invention or the means for correcting the fluctuation of the spherical aberration and the axial chromatic aberration) is corrected by changing the interval. Further, by providing a diffraction surface on the surface of the objective lens 3 on the light source side, the above-mentioned spherical aberration is more favorably corrected. Further, deterioration of the spherical aberration of the objective lens when the wavelength of the light source fluctuates or when the temperature and humidity change is corrected well by changing the interval of the divergence changing means. That is, Table 8
As is clear from FIG. 5, by changing the interval between the negative lens 5 and the positive lens 4 to an appropriate interval, the spherical aberration degradation of the objective lens 3 when the substrate thickness is changed, when the wavelength changes, and when the temperature and humidity changes
Corrected well. Also, by using a plastic material for the objective lens 3, the negative lens 5, and the positive lens 4,
The weight of the optical system and the load on the movable mechanism are reduced.

[Table 8]

(Example 5) Table 9 shows that
The data on the optical system including the negative lens 5, the positive lens 4, and the objective lens 3 is shown.

[Table 9]

FIGS. 12 and 13 are optical system configuration diagrams of the negative lens 5, the positive lens 4, and the objective lens 3 according to the fifth embodiment. FIGS. 14 and 15 are diagrams of spherical aberration applied to the objective lens 3 when recording or reproducing information on different optical information recording media, respectively. In the fifth embodiment, using the same optical system, the first light source 1 having a wavelength of 405 nm is used.
Information is recorded or reproduced by a combination of No. 1 and an optical information recording medium having a transparent substrate thickness of 0.1 mm, or a combination of the second light source 11 having a wavelength of 655 nm and an optical information recording medium having a transparent substrate thickness of 0.6 mm. It is an example of an optical pickup device. In Example 5, as materials of the negative lens 5 and the positive lens 4, νdN = 30.0 and νdP = 5, respectively.
By selecting the material of 6.5, longitudinal chromatic aberration is corrected. In this embodiment, fN = −6.59 (m
m), fP = 9.85 (mm), and f1 = 3.01
1 (mm) and fD1 = 84966.33 (mm). Note that the focal length of the objective lens at the oscillation wavelength λ2 = 655 nm is f2 = 3.076.

As is clear from Table 10, by changing the interval between the negative lens 5 and the positive lens 4 to an appropriate interval as in the case of the fourth embodiment, it is possible to change the thickness of the transparent substrate, the wavelength change, and the temperature and humidity change. The deterioration of the spherical aberration of the objective lens at the time can be satisfactorily corrected. Further, by using a plastic material for the objective lens 3, the negative lens 5, and the positive lens 4, the weight of the optical system is reduced and the load on the movable mechanism is reduced.

[Table 10]

The light beam incident on the negative lens 5 as a means for correcting the fluctuation of the spherical aberration is not limited to the parallel light as in the above-described embodiment, but may be a divergent light or a convergent light. Optical systems can be applied as well. Although not shown in this embodiment, a coupling lens that changes the degree of divergence of the light beam from the light source can be provided between the light source and the spherical aberration correction unit. By adding a diffractive surface to such a coupling lens to provide a diffractive lens having a shorter back focus on the long wavelength side, axial chromatic aberration generated by the objective lens can be corrected.

The coupling lens used in the optical system according to the present invention is not limited to the above-described embodiment, but may be any as described in Japanese Patent Application No. 2000-060843 by the same applicant.
The axial chromatic aberration generated in the objective lens 3 can be corrected more favorably.

Further, between the coupling lens and the means for correcting the fluctuation of the spherical aberration (the negative lens 5 and the positive lens 4), the astigmatic difference of the light beam from the light source is reduced, and the spherical aberration correcting means is substantially circular. When a beam shaping element capable of receiving the light beam is provided, the divergence of the light beam from the coupling lens changes due to the focal point movement of the coupling lens caused by a change in temperature and humidity, and the beam shaping element causes astigmatism. Will occur. In order to suppress this, by using a coupling lens as disclosed in Japanese Patent Application No. 2000-053858 filed by the same applicant, it is possible to suppress the occurrence of astigmatism due to the beam shaping element.

In the fourth and fifth embodiments, the light source wavelength 65
Aberration diagrams for an optical information recording medium having a thickness of 5 nm and a transparent substrate thickness of 0.6 mm are illustrated up to NA of 0.65. But,
At this time, the objective lens 3 has a light source wavelength of 405 nm and an NA of
A light beam that passes through all apertures determined by 0.85 is incident. A light beam having an NA of 0.65 or more that does not contribute to image formation is formed into a flare component by utilizing the effect of the diffraction surface provided on the objective lens 3, so that the spot diameter is not excessively reduced on the information recording surface, and the optical pickup device is used. Detection of unnecessary signals by the light receiving element can be prevented.

(Example 6) Table 11 shows data relating to an optical system including a negative lens 5, a positive lens 4, and an objective lens 3 in Example 6.

[Table 11]

FIG. 16 shows the negative lens 5 according to the sixth embodiment,
FIG. 2 is an optical system configuration diagram of a positive lens 4 and an objective lens 3. FIG. 17 is a diagram of spherical aberration applied to the objective lens 3. In the sixth embodiment, information is recorded or reproduced by a combination of the first light source 11 having a wavelength of 405 nm and the image-side numerical aperture NA of the objective lens 3 of 0.85. In the sixth embodiment, the diffractive surface is added to the surface of the positive lens 4 on the side of the optical information recording medium, and the diffractive lens has a shorter back focus on the longer wavelength side, so that the axial chromatic aberration of the objective lens 3 can be reduced. Has been corrected. Further, in the present embodiment, fN = −
5.03 (mm), fP = 6.81 (mm), and f
= 1.765 (mm).

The correction of the variation of the light source wavelength or the variation of the spherical aberration due to the temperature change in the present embodiment is the same as that of the first embodiment, and the explanation is omitted. As is clear from Table 12, the spherical aberration at the time of wavelength change or temperature change is good. Also, an objective lens 3, a negative lens 5,
By using a plastic material for the positive lens 4, the weight of the optical system is reduced and the burden on the movable mechanism is reduced.

[Table 12]

(Example 7) Table 13 shows data relating to an optical system including a negative lens 5, a positive lens 4, and an objective lens 3 in Example 7.

[Table 13]

FIG. 18 shows a negative lens 5 according to Example 7,
FIG. 2 is an optical system configuration diagram of a positive lens 4 and an objective lens 3. FIG. 19 is a diagram of spherical aberration applied to the objective lens 3. In the seventh embodiment, information is recorded or reproduced by a combination of the first light source 11 having a wavelength of 405 nm and the image-side numerical aperture NA of the objective lens 3 of 0.85. In the seventh embodiment, axial chromatic aberration of the objective lens 3 is corrected by adding a diffractive surface to both surfaces of the positive lens 4 and using a diffractive lens having a shorter back focus on the longer wavelength side.
In this embodiment, fN = −4.89 (m
m), fP = 5.83 (mm), f = 1.765
(Mm).

The correction of the fluctuation of the light source wavelength or the fluctuation of the spherical aberration at the time of the temperature change in this embodiment is the same as that of the first embodiment, and the explanation is omitted. As is clear from Table 14, the spherical aberration at the time of wavelength change or temperature change is good. Also, an objective lens 3, a negative lens 5,
By using a plastic material for the positive lens 4, the weight of the optical system is reduced and the burden on the movable mechanism is reduced.

[Table 14]

(Embodiment 8) Table 15 shows data relating to the optical system including the negative lens 5, the positive lens 4, and the objective lens 3 in Embodiment 8.

[Table 15]

FIG. 20 shows a negative lens 5 according to Example 8;
FIG. 2 is an optical system configuration diagram of a positive lens 4 and an objective lens 3. FIG. 21 is a diagram of spherical aberration applied to the objective lens 3. In the eighth embodiment, information is recorded or reproduced by a combination of the first light source 11 having a wavelength of 405 nm and the image-side numerical aperture NA of the objective lens 3 of 0.85. In the eighth embodiment, axial chromatic aberration of the objective lens 3 is corrected by adding a diffractive surface to both surfaces of the negative lens 5 and the positive lens 4 so as to shorten the back focus on the long wavelength side. ing. Further, in the present embodiment, fN = −
5.54 (mm), fP = 7.42 (mm), and f
= 1.765 (mm).

The correction of the spherical aberration at the time of light source length fluctuation or temperature change in this embodiment is the same as that of the first embodiment, and the description is omitted. As is apparent from Table 16, the spherical aberration at the time of wavelength change or temperature change is good. Further, by using a plastic material for the objective lens 3, the negative lens 5, and the positive lens 4, the weight of the optical system is reduced and the load on the movable mechanism is reduced.

[Table 16]

(Embodiment 9) Table 17 shows data related to the optical system including the negative lens 5, the positive lens 4, and the objective lens 3 in Embodiment 9.

[Table 17]

FIG. 22 shows the negative lens 5 according to the ninth embodiment,
FIG. 2 is an optical system configuration diagram of a positive lens 4 and an objective lens 3. FIG. 23 is a diagram of spherical aberration applied to the objective lens 3. In the ninth embodiment, information is recorded or reproduced by a combination of the first light source 11 having a wavelength of 405 nm and the image-side numerical aperture NA of the objective lens 3 of 0.85. In the ninth embodiment, the diffractive surface is added to the surface of the positive lens 4 on the side of the optical information recording medium, and the back focus is shortened on the long wavelength side, so that the axial chromatic aberration of the objective lens 3 is reduced. Has been corrected. Further, as materials of the negative lens 5 and the positive lens 4 of the spherical aberration correcting means, N = 30.
By selecting a material of 0, P = 56.5, the longitudinal chromatic aberration of the objective lens is more properly corrected. In this embodiment, fN = -4.15 (mm) and fP = 5.91.
(Mm), and f = 1.765 (mm).

The correction of the variation of the light source wavelength or the variation of the spherical aberration due to the temperature change in the present embodiment is the same as that of the first embodiment, and the description is omitted. As is clear from Table 18, the spherical aberration at the time of wavelength change or temperature change is good. Also, an objective lens 3, a negative lens 5,
By using a plastic material for the positive lens 4, the weight of the optical system is reduced and the burden on the movable mechanism is reduced.

[Table 18]

(Embodiment 10) Table 19 shows data relating to the optical system including the negative lens 5, the positive lens 4, and the objective lens 3 in Embodiment 10.

[Table 19]

FIG. 24 shows a negative lens 5 according to the tenth embodiment.
FIG. 3 is an optical system configuration diagram of a positive lens 4 and an objective lens 3. FIG. 25 is a diagram of spherical aberration applied to the objective lens 3. In the tenth embodiment, information is recorded or reproduced by a combination of the first light source 11 having a wavelength of 405 nm and the image-side numerical aperture NA of the objective lens 3 of 0.85.
In the tenth embodiment, axial chromatic aberration of the objective lens 3 is corrected by adding a diffractive surface to both surfaces of the positive lens 4 and making the back focus shorter on the long wavelength side. At this time, the axial chromatic aberration of the combined system including the objective lens 3 and the negative lens 5 and the positive lens 4 as the spherical aberration correcting means is overcorrected, as shown in FIG. The oscillation wavelength of one light source 11 (405n
m) intersects with the spherical aberration curves on the long and short wavelength side. Due to this, the mode hop phenomenon of the light source and the deterioration of the wavefront aberration at the time of high frequency superposition are extremely small,
For example, even when the oscillation wavelength of the light source fluctuates slightly, the movement of the optimum writing position can be suppressed to a small value. Further, by using a double-sided aspherical lens for the negative lens 5, which is a movable element as a spherical aberration correcting means, the eccentricity of the negative lens 5 and the deterioration of wavefront aberration at the time of tracking error are suppressed to a small extent. The longitudinal chromatic aberration of the objective lens 3 is corrected by selecting a material of νdN = 24.3 and νdP = 56.5 as a material of the negative lens 5 and the positive lens 4, respectively. This reduces the burden on the diffractive structure. In this embodiment, fN = −7.78.
(Mm), fP = 9.95 (mm), and f = 1.7
65 (mm).

In this embodiment, the stop for restricting the light beam is arranged on the optical information recording medium side from the vertex of the light source side surface of the objective lens 3, so that when the divergent light beam enters, the objective lens 3 The light passage height of the surface closest to the light source can be kept small. This is preferable in terms of reducing the diameter of the objective lens 3 or correcting aberrations.

The correction of the variation of the spherical aberration due to the wavelength variation of the light source or the temperature variation in the present embodiment is described in the first embodiment.
Therefore, the description is omitted. As is clear from Table 20, the spherical aberration at the time of wavelength change or temperature change is good. Further, by using a plastic material for the objective lens 3, the negative lens 5, and the positive lens 4, the weight of the optical system is reduced and the burden on the movable mechanism is reduced.
In addition, since a plastic material having a high transmittance for short-wavelength light is used, an optical system that can be mass-produced at low cost and has high light use efficiency has been achieved. Note that the movable mechanism is a moving device of the negative lens 5 and a focusing mechanism of the objective lens 3 in the embodiments in this specification.

[Table 20]

Although not shown in FIG. 25 in this embodiment, as shown in the embodiment of FIG. 1, in an actual optical pickup device, a light source and a spherical aberration correcting means are provided between the light source and the spherical aberration correcting means. A coupling lens such as a collimator is provided. In this case, axial chromatic aberration generated in the coupling lens can also be corrected by the configuration of the present embodiment, and a converging optical system with good chromatic aberration can be obtained.

Further, two phase change films of a first information recording layer and a second information recording layer are provided on one side of the optical information recording medium,
There is known an optical information recording medium of a so-called two-layer recording system in which the recording capacity of the optical information recording medium is approximately doubled by recording information on each of them. It can also be applied to record or reproduce information on or from an optical information recording medium of such a two-layer recording system, and corrects spherical aberration caused by a difference in thickness up to the information recording surface of each information recording layer. can do. For example, assuming that the first information recording layer and the second information recording layer are arranged in this order from the surface side of the optical information recording medium, as shown in FIG. 26, the distance between the negative lens 5 and the positive lens 4 as the spherical aberration correcting means is set. By reducing the size, information can be recorded or reproduced on the information recording surface of the second information recording layer.

(Embodiment 11) Table 21 shows data related to the optical system including the negative lens 5, the positive lens 4, and the objective lens 3 in the eleventh embodiment.

[Table 21]

FIG. 27 shows a negative lens 5 according to the eleventh embodiment.
FIG. 3 is an optical system configuration diagram of a positive lens 4 and an objective lens 3. FIG. 28 is a diagram of spherical aberration applied to the objective lens 3. In the eleventh embodiment, information is recorded or reproduced by a combination of the first light source 11 having a wavelength of 405 nm and the image-side numerical aperture NA of the objective lens 3 of 0.85.
In Example 11, the axial chromatic aberration of the objective lens 3 is corrected by adding a diffractive surface to the light source side surface of the objective lens 3 and making the back focus shorter on the long wavelength side. I have. Further, by using a double-sided aspherical lens for the negative lens 5, which is a movable element as a spherical aberration correcting means, the eccentricity of the negative lens 5 and the deterioration of wavefront aberration at the time of tracking error are suppressed to a small extent. In this embodiment, fN = −8.32 (mm) and fP = 12.30.
(Mm), f = 1.765 (mm), fD = 2
8.417 (mm).

The correction of the variation of the spherical aberration due to the wavelength variation of the light source or the temperature variation in the present embodiment is described in the first embodiment.
Therefore, the description is omitted. As is clear from Table 22, the spherical aberration at the time of wavelength change or temperature change is good. In addition, by using a plastic material for the objective lens 3, the negative lens 5, and the positive lens 4, the weight of the optical system is reduced and the load on the movable mechanism is reduced.
Further, since a plastic material having a high transmittance for short-wavelength light is used, an optical system that can be mass-produced at low cost and has high light use efficiency is achieved.

[Table 22]

(Embodiment 12) Table 23 shows data related to the optical system including the negative lens 5, the positive lens 4, and the objective lens 3 in Embodiment 12.

[Table 23]

FIGS. 29 and 30 are optical system diagrams of the negative lens 5, the positive lens 4, and the objective lens 3 according to the twelfth embodiment. FIGS. 31 and 32 are diagrams of spherical aberration applied to the objective lens 3 when recording or reproducing information on different optical information recording media, respectively. In Example 12, using the same optical system, a combination of the first light source 11 having a wavelength of 405 nm and an optical information recording medium having a transparent substrate thickness of 0.1 mm, or a combination of the second light source 11 having a wavelength of 655 nm and the transparent substrate thickness This is an example of an optical pickup device that records or reproduces information in combination with a 0.6 mm optical information recording medium. In the twelfth embodiment, by providing a diffraction structure on the light source side of the objective lens 3, spherical aberration and chromatic spherical aberration caused by a difference in the thickness of the transparent substrate are corrected. Specifically, by moving the negative lens 5 as a spherical aberration correcting means in the optical axis direction, the divergence angle of the light beam incident on the objective lens 3 is changed according to the thickness of the transparent substrate of the optical information recording medium. Do. In the present embodiment,
fN = -6.39 (mm), fP = 10.51 (mm)
Where f1 = 1.765 (mm) and fD1 = 45.4.
6 (mm). Note that the focal length of the objective lens at the oscillation wavelength λ2 = 655 nm is f2 = 1.79.

The correction of the variation of the spherical aberration due to the wavelength variation of the light source or the temperature variation in the present embodiment is described in the first embodiment.
Therefore, the description is omitted. As is clear from Table 24, the spherical aberration at the time of wavelength change or temperature change is good. Further, by using a plastic material for the objective lens 3, the negative lens 5, and the positive lens 4, the weight of the optical system is reduced and the burden on the movable mechanism is reduced.
Further, since a plastic material having a high transmittance for short-wavelength light is used, an optical system that can be mass-produced at low cost and has high light use efficiency is achieved.

[Table 24]

As in the fourth and fifth embodiments, the light source wavelength 65
A light beam having an NA of 0.65 or more for an optical information recording medium having a thickness of 5 nm and a transparent substrate thickness of 0.6 mm is formed into a flare component by utilizing the effect of the diffraction surface provided on the objective lens 3, thereby obtaining a spot diameter on the information recording surface. Thus, it is possible to prevent the unnecessary signal from being detected by the light receiving element of the optical pickup device.

(Thirteenth Embodiment) Table 25 shows data on the optical system including the coupling lens 21 or the collimator corresponding to the coupling lenses 15 and 21, the negative lens 5, the positive lens 4, and the objective lens 3 in the thirteenth embodiment. Is shown.

[Table 25]

FIG. 33 shows a collimator according to the thirteenth embodiment.
FIG. 2 is an optical system configuration diagram of a negative lens 5, a positive lens 4, and an objective lens 3. FIG. 34 is a diagram of spherical aberration applied to the objective lens 3. In the thirteenth embodiment, the first light source 11 having the wavelength of 405 nm and the image-side numerical aperture NA of the objective lens 3 are 0.85.
Recording or reproduction of information is performed in combination with the above. In the thirteenth embodiment, the divergence angle of the light beam incident on the objective lens 3 is changed by moving the negative lens 5 in the spherical aberration correcting means along the optical axis direction, and the condensing optical system (collimator and objective lens) The variation of the spherical aberration generated on each optical surface in 3) is corrected. In the present embodiment, fN = -10.71 (mm), fP = 1
3.18 (mm) and f = 1.765 (mm).

Also, diffractive surfaces are added to both surfaces of the positive lens 4, and the spherical aberration correcting means itself generates axial chromatic aberration having a polarity opposite to that of the axial chromatic aberration generated on the optical surface of the condensing optical system. On the other hand, axial chromatic aberration generated on the optical surface of the condensing optical system was corrected, and axial chromatic aberration of the wavefront when focused on the information recording surface was improved. In the focusing optical system of the present embodiment,
The amounts of longitudinal chromatic aberration generated by the collimator and the objective lens 3 as the optical elements are represented by ΔfB1 and ΔfB2, respectively.
When the ratio was roughly calculated, the focal length of the collimator was 12 mm, and the magnification of the spherical aberration correcting means was 1.23.
Since the distance between the various points of the objective lens is 1.765 mm, ΔfB1 / ΔfB2 = 1/30. That is,
If the absolute value of the axial chromatic aberration of the opposite polarity generated by the spherical aberration correction means is made substantially the same as the absolute value of the axial chromatic aberration generated by the objective lens, the axial chromatic aberration of the wavefront when focused on the information recording surface Can be improved. At this time, as shown in FIG. 34, the axial chromatic aberration of the combined system including the condensing optical system and the negative lens 5 and the positive lens 4 as the spherical aberration correcting means is overcorrected. The spherical aberration curve of the oscillation wavelength (405 nm) of the first light source 11 intersects the spherical aberration curve on the long / short wavelength side. Accordingly, the mode hop phenomenon of the light source and the deterioration of the wavefront aberration at the time of high-frequency superposition are extremely small. For example, even when the oscillation wavelength of the light source slightly changes, the movement of the optimum writing position can be suppressed to a small value. Further, the negative lens 5, which is a movable element in the spherical aberration correcting means, is a double-sided aspherical lens, so that the eccentricity of the negative lens 5 and the deterioration of the wavefront aberration at the time of tracking error are suppressed.

As is clear from Table 26, it is possible to correct the fluctuation of the spherical aberration occurring on each optical surface of the light-converging optical system due to various factors such as a wavelength change or a temperature change, and a good spherical aberration is obtained. I have. Further, by using a plastic material for all of the collimator and the objective lens 3 constituting the condensing optical system and the negative lens 5 and the positive lens 4 constituting the spherical aberration correcting means, the weight of the optical system can be reduced and the movable mechanism can be reduced. The burden is reduced. In addition, since a plastic material having a high transmittance for short-wavelength light is used, an optical system that can be mass-produced at low cost and has high light use efficiency has been achieved.

[Table 26]

In the present embodiment, the negative lens 5 in the spherical aberration correcting means is movable. However, the positive lens 4 may be movable and the two lenses may be movable. Variations in spherical aberration of the optical optical system can be corrected. Further, in the present embodiment, the axial chromatic aberration of the condensing optical system and the spherical aberration correcting means is corrected by the diffraction structure provided in the positive lens 4 in the spherical aberration correcting means. And an optical element having a surface provided with a diffractive structure may be additionally provided.

(Embodiment 14) Table 27 shows data relating to the optical system including the coupling lens 15, the negative lens 5, the positive lens 4, and the objective lens 3 in Embodiment 14.

[Table 27]

FIG. 35 is an optical system configuration diagram of the coupling lens 15, the negative lens 5, the positive lens 4, and the objective lens 3 according to Example 14. The coupling lens 15 of the present embodiment has a function of converting a strong divergent light beam from the first light source 11 into a weak divergent light beam. FIG. 36 shows the objective lens 3
4 is a spherical aberration diagram according to FIG. In the fourteenth embodiment, information is recorded or reproduced by a combination of the first light source 11 having a wavelength of 405 nm and the image-side numerical aperture NA of the objective lens 3 of 0.85. In the fourteenth embodiment, the divergence angle of the light beam incident on the objective lens 3 is changed by moving the negative lens 5 in the spherical aberration correcting means along the optical axis direction, and the condensing optical system (the coupling lens 15 Further, the fluctuation of the spherical aberration generated on each optical surface of the objective lens 3) is corrected. In the present embodiment, fN = −1
4.67 (mm), fP = 11.66 (mm),
f = 1.765 (mm).

Also, diffractive surfaces are added to both surfaces of the positive lens 4, and the spherical aberration correcting means itself generates axial chromatic aberration having a polarity opposite to that of axial chromatic aberration generated on the optical surface of the condensing optical system. On the other hand, axial chromatic aberration generated on the optical surface of the condensing optical system was corrected, and axial chromatic aberration of the wavefront when focused on the information recording surface was improved. At this time, the axial chromatic aberration of the combined system in which the condensing optical system and the negative lens 5 and the positive lens 4 as the spherical aberration correcting unit are combined is overcorrected, and thus, FIG.
As shown in FIG. 6, the oscillation wavelength of the first light source 11 (4
(05 nm) and the spherical aberration curve on the long / short wavelength side. As a result, the mode hop phenomenon of the light source and the deterioration of the wavefront aberration at the time of high-frequency superposition are extremely small. For example, even when the oscillation wavelength of the light source slightly fluctuates,
The movement of the optimum writing position can be kept small.

As is clear from Table 28, it is possible to correct the fluctuation of the spherical aberration generated on each optical surface of the light-converging optical system due to various factors such as a change in wavelength or a change in temperature. I have. Further, by using a plastic material for all of the coupling lens 15 and the objective lens 3 constituting the condensing optical system and the negative lens 5 and the positive lens 4 constituting the spherical aberration correcting means, the optical system can be made lighter and movable. The burden on the mechanism is reduced. In addition, since a plastic material having a high transmittance for short-wavelength light is used, an optical system that can be mass-produced at low cost and has high light use efficiency has been achieved. Further, in this embodiment, since the light incident on the spherical aberration correcting means is a weak divergent light beam, the power of the coupling lens 15 and the power of the negative lens 5 in the spherical aberration correcting means can be small, and each lens can be used. The deterioration of the wavefront aberration due to the eccentricity can be suppressed small.

[Table 28]

In the present embodiment, the negative lens 5 in the spherical aberration correcting means is movable. However, the positive lens 4 may be movable, and both lenses may be movable. Variations in spherical aberration of the optical optical system can be corrected. Further, in the present embodiment, the axial chromatic aberration of the condensing optical system and the spherical aberration correcting means is corrected by the diffraction structure provided in the positive lens 4 in the spherical aberration correcting means. And an optical element having a surface provided with a diffractive structure may be additionally provided.

In each of the above-described embodiments, a beam expander is used as the spherical aberration correcting means, and the beam expander includes a movable single-lens negative lens and a single-lens positive lens. Although an example is shown, it is needless to say that the present invention is not limited to this, and may be a configuration including two or more lens groups including a plurality of lenses, and various modifications are possible without departing from the present invention. It is.

FIG. 37 is a diagram showing an optical system according to another embodiment. An element SE for correcting fluctuation of spherical aberration between the coupling lens CL and the objective lens OL.
Is inserted. Such an optical system includes the negative lens 5 of FIG.
It can be used in place of the positive lens 4 and the objective lens 3.

The element SE is provided between the four glass plates SE4 from the coupling lens CL side in the X-direction liquid crystal element SE.
The half-wave plate SE2 and the Y-direction liquid crystal element SE3 are sandwiched therebetween. By electrically driving both liquid crystal elements SE1 and SE2, it is possible to correct the fluctuation of the spherical aberration. Further, by providing a ring-shaped diffraction structure (not shown) on the surface of the coupling lens CL on the side of the objective lens, chromatic aberration having a phase opposite to that of the axial chromatic aberration generated by the objective lens OL, that is, over-wave on the short wave town side. On the long wavelength side, under-axial chromatic aberration can be generated. As a result, the axial chromatic aberration is canceled, so that the wavefront when transmitted through the element SE for correcting the fluctuation of the spherical aberration and the objective lens OL and focused on the optical information recording medium (not shown) becomes A state is obtained in which the bearing chromatic aberration is suppressed to a small value.

FIG. 38 is a diagram showing an optical system according to a modification of the present embodiment. In FIG. 38, the objective lens OL and the element SE for correcting the fluctuation of the spherical aberration are shown in FIG.
The description is omitted because it is the same as the embodiment shown in FIG. In FIG. 38, the coupling lens CL has a configuration in which the negative lens CL1 and the positive lens CL2 are bonded to each other, and the Abbe number νdN of the negative lens CL1 and the positive lens C
The relationship of νdN <νdP holds with the Abbe number νdP of L2.

Thus, the negative lens CL1 and the positive lens CL
By adjusting the Abbe number of 2, it is possible to generate chromatic aberration having a phase opposite to that of the axial chromatic aberration generated in the objective lens OL, that is, axial chromatic aberration that is over on the short wave side and under on the long wavelength side. As a result, the axial chromatic aberration is canceled, so that the wavefront when transmitted through the element SE for correcting the fluctuation of the spherical aberration and the objective lens OL and focused on the optical information recording medium (not shown) becomes A state is obtained in which the bearing chromatic aberration is suppressed to a small value.

FIG. 39 is a sectional view (a) schematically showing an objective lens 3 'usable in the optical pickup device of the present embodiment and a front view (b) as viewed from the light source side. [The chain line indicates the optical axis. ]

The objective lens 3 'can correct spherical aberration fluctuation due to a difference in the thickness of the transparent substrate of different optical information recording media. In FIG. 36, the refracting surface S1 on the light source side and the refracting surface S2 on the optical disk are both convex lenses having an aspheric shape and having a positive refractive power.
The refraction surface S1 on the light source side of the objective lens is composed of four divided surfaces b1 to b4 concentrically with the optical axis. The boundary between the divided surfaces is provided with a step to form each divided surface. Accordingly, the spherical aberration and the wavefront aberration of the objective lens have a step at a position corresponding to the boundary.

In a normal objective lens, occurrence of spherical aberration due to the difference in the thickness of the transparent substrate of different optical information recording media is inevitable. However, although the objective lens 3 'used in this embodiment cannot completely correct spherical aberration,
As will be described next, it is designed to further reduce such aberration.

First, when reproducing and / or recording information from / to the first optical information recording medium, the refracting surfaces S1 and S1 are adjusted so that the spherical aberration component of the wavefront aberration is within 0.05λ1rms at the best image plane position. The refraction surface S2 is designed. The refraction surface S1 designed in this manner is divided into the first divided surface b1 and the fourth
Applies to split plane b4. Then, the transparent substrate thickness t3 (t1
A new refraction surface S1 'is designed without using the refraction surface S2 as a variable so that the spherical aberration component of the wavefront aberration is within 0.05λ2 rms at the best image plane position at ≦ t3 ≦ t2).

The refracting surface S1 'is the second divided surface b2 and the third divided surface b3. Since the refraction surface S1' is optimized by the transparent substrate thickness t3, the first divided surface b is used when the first optical disk 10 is used. The best image plane position is apparently formed at a position different from the best image plane position formed by the surface b1 and the fourth divided surface b4. However, the wavefront aberration changes the slope of the wavefront aberration in the division plane. For example, in a first optical information recording medium (for example, a next-generation optical disk having a higher density and a larger capacity than a DVD), the wavefront aberration is lowered to the right. On the other hand, the second optical information recording medium (for example, DVD) slightly rises to the right. By providing two or more such divided surfaces on the refraction surface S1, it is easy to achieve both wavefront aberrations in different optical information recording media.

By appropriately designing the boundary positions of these divided surfaces and the axial thickness of the divided surfaces, the beam spot minimum confusion circle position for the next-generation optical disk having a higher density and larger capacity than the DVD, and the front focus position for the DVD. In each case, the wavefront aberration can be corrected. That is, in a next-generation optical disk having a higher density and a larger capacity than a DVD, the first to fourth light beams LB1 to LB1
The light beam in LB4 is substantially an integral multiple of wavelength λ1 at the position of the circle of least confusion, ie, miλ1 (mi is an integer and i =
1, 2,..., K).

In the case of DVD, the required numerical aperture NA2 is NA
Therefore, all of the first to fourth light beams LB1 to LB4 do not have to be effectively used. In the optical pickup device of the present embodiment, the light beams in the first to third light beams LB1 to LB3 are At the position, almost an integral multiple of the wavelength λ2 niλ1
(Ni is an integer, i = 1, 2,..., K) and has a wavefront aberration. The fourth light beam LB4 is unnecessary light in the case of a DVD, and irradiates as a flare a place spaced from the main spot light on the recording surface of the optical disc. This flare is sufficiently small with respect to the main spot light.
By simply setting the numerical aperture of the next generation optical disk having a higher density and a larger capacity than that of the VD, DVD reproduction can be performed without the need for a means for changing the numerical aperture of the stop 8. Of course, DV
A stop 8 having a function of blocking the fourth light beam LB4 when using D
May be used.

Therefore, the optical pickup device of this embodiment is
Although four divided surfaces b1 to b4 are provided, unlike the objective lens of the related art, since each disk does not have a plurality of focal positions, spot light loss can be reduced. When each optical disc is used, the wavefront aberration of the light beam within the required numerical aperture is substantially multiplied by an integral number of wavelengths, and the luminous fluxes passing through the required numerical aperture interfere with each other and strengthen each other, so that the center intensity of the spot light is increased. A sufficient amount of reflected light can be obtained from the optical disc, and stable operation as a compatible optical pickup device is possible.

In the present embodiment, the objective lens is provided with four divided surfaces. However, basically, the incident light beam is divided into three light beams so as to have three divided surfaces.
An objective having a surface having two portions can also be used for the objective of the present invention. For example, at least a first portion, a second portion, and a third portion that divide a light beam emitted from a light source by refraction into a plurality of light beams in order from at least one surface toward an outer periphery thereof from an optical axis side. And the first and third portions have a transparent substrate thickness t
A light beam from a light source can be focused on the information recording surface of the first optical information recording medium so that information can be recorded or reproduced on the information recording surface of the first optical information recording medium. The portion 1 and the second portion have a transparent substrate thickness t2 (t1 <
The light beam from the light source can be focused on the information recording surface so that information can be recorded or reproduced on the information recording surface of the second optical information recording medium at t2). Is a well-known objective lens.

According to the present embodiment described above, the optical pickup device and the optical system which can effectively correct the fluctuation of the spherical aberration caused by the mode hop of the semiconductor laser,
An optical pickup device and an optical system capable of effectively correcting the fluctuation of the spherical aberration of the objective lens caused by a humidity change or the like, comprising a short-wavelength laser and a high NA objective lens, and recording or recording information on different optical information recording media. An optical pickup device capable of reproducing can be provided. The present invention is, of course, not limited to the above embodiments and various examples.

[0239]

According to the present invention, fluctuations in spherical aberration can be effectively corrected in an optical pickup device.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an optical pickup device according to an embodiment.

FIG. 2 shows a negative lens 5 and a positive lens 4 according to the first embodiment;
FIG. 3 is an optical system configuration diagram of an objective lens 3.

FIG. 3 is a diagram of spherical aberration applied to the objective lens 3 according to the optical system of Example 1.

FIG. 4 shows a negative lens 5 and a positive lens 4 according to a second embodiment;
FIG. 3 is an optical system configuration diagram of an objective lens 3.

FIG. 5 is a spherical aberration diagram of the objective lens 3 according to the optical system of Example 2.

FIG. 6 shows a negative lens 5 and a positive lens 4 according to Example 3,
FIG. 3 is an optical system configuration diagram of an objective lens 3.

FIG. 7 is a spherical aberration diagram of the objective lens 3 according to the optical system of Example 3.

FIG. 8 shows a negative lens 5 and a positive lens 4 according to Example 4,
FIG. 3 is an optical system configuration diagram of an objective lens 3.

FIG. 9 shows a negative lens 5 and a positive lens 4 according to Example 4,
FIG. 3 is an optical system configuration diagram of an objective lens 3.

FIG. 10 is a spherical aberration diagram of the objective lens 3 according to the optical system of Example 4.

FIG. 11 is a spherical aberration diagram of the objective lens 3 according to the optical system of Example 4.

FIG. 12 shows a negative lens 5 and a positive lens 4 according to Example 5.
FIG. 2 is a diagram illustrating an optical system configuration of an objective lens 3.

FIG. 13 shows a negative lens 5 and a positive lens 4 according to Example 5.
FIG. 2 is a diagram illustrating an optical system configuration of an objective lens 3.

FIG. 14 is a diagram showing spherical aberration of the objective lens 3 according to the optical system of Example 5;

FIG. 15 is a diagram of spherical aberration applied to the objective lens 3 according to the optical system of Example 5;

FIG. 16 shows a negative lens 5 and a positive lens 4 according to Example 6.
FIG. 2 is a diagram illustrating an optical system configuration of an objective lens 3.

FIG. 17 is a spherical aberration diagram of the objective lens 3 according to the optical system of Example 6;

FIG. 18 shows a negative lens 5 and a positive lens 4 according to Example 7.
FIG. 2 is a diagram illustrating an optical system configuration of an objective lens 3.

FIG. 19 is a diagram depicting the spherical aberration of the objective lens 3 according to the optical system of Example 7;

FIG. 20 shows a negative lens 5 and a positive lens 4 according to Example 8.
FIG. 2 is a diagram illustrating an optical system configuration of an objective lens 3.

FIG. 21 is a diagram showing spherical aberration of the objective lens 3 according to the optical system of Example 8;

FIG. 22 shows a negative lens 5 and a positive lens 4 according to Example 9;
FIG. 2 is a diagram illustrating an optical system configuration of an objective lens 3.

FIG. 23 is a spherical aberration diagram of the objective lens 3 according to the optical system of Example 9;

FIG. 24 shows a negative lens 5 and a positive lens 4 according to Example 10.
FIG. 2 is a diagram illustrating an optical system configuration of an objective lens 3.

FIG. 25 is a spherical aberration diagram of the objective lens 3 according to the optical system of Example 10.

FIG. 26 shows a negative lens 5 and a positive lens 4 according to Example 10.
FIG. 2 is a diagram illustrating an optical system configuration of an objective lens 3.

FIG. 27 shows a negative lens 5 and a positive lens 4 according to Example 11;
FIG. 2 is a diagram illustrating an optical system configuration of an objective lens 3.

FIG. 28 is a diagram depicting the spherical aberration of the objective lens 3 according to the optical system of Example 11;

FIG. 29 shows a negative lens 5 and a positive lens 4 according to Example 12.
FIG. 2 is a diagram illustrating an optical system configuration of an objective lens 3.

FIG. 30 shows a negative lens 5 and a positive lens 4 according to Example 12.
FIG. 2 is a diagram illustrating an optical system configuration of an objective lens 3.

FIG. 31 is a diagram depicting the spherical aberration of the objective lens 3 according to the optical system of Example 12;

FIG. 32 is a diagram depicting the spherical aberration of the objective lens 3 according to the optical system of Example 12;

FIG. 33 shows a collimator and a negative lens 5 according to Example 13.
FIG. 3 is an optical system configuration diagram of a positive lens 4 and an objective lens 3.

FIG. 34 is a diagram depicting the spherical aberration of the objective lens 3 according to the optical system of Example 13;

FIG. 35 shows a collimator and a negative lens 5 according to Example 14.
FIG. 3 is an optical system configuration diagram of a positive lens 4 and an objective lens 3.

FIG. 36 is a diagram depicting the spherical aberration of the objective lens 3 according to the optical system of Example 14;

FIG. 37 is a diagram showing an optical system according to another embodiment.

FIG. 38 is a diagram showing an optical system according to a modification of the present embodiment.

FIG. 39 is a cross-sectional view schematically showing an objective lens 3 ′ usable in the optical pickup device of the present embodiment, and a front view (b) as viewed from the light source side.

[Explanation of symbols]

3 Objective Lens 4 Positive Lens 5 Negative Lens 6 Objective Lens Actuator 7 Negative Lens Actuator 8 Aperture 9 Cylindrical Lens 11 First Light Source 12 Second
Light source 15 Coupling lens 16 Concave lens 17 Hologram 21 Coupling lens 41, 42 Photodetector 62 Beam splitter 71, 72 1/4 wavelength plate

Claims (134)

[Claims] An optical information recording system comprising: a light source; an optical lens including an objective lens for converging a light beam emitted from the light source onto an information recording surface via a transparent substrate of an optical information recording medium; An optical pickup device having a photodetector for receiving reflected light from a medium, wherein the objective lens includes at least one lens made of a plastic material, between the light source and the objective lens. , Temperature -30 ° C ~ +
Means for correcting a change in spherical aberration caused by a change in at least one of the shape and refractive index of the objective lens and a change in oscillation wavelength of the light source with respect to an environmental change between 85 ° C. and a humidity of 5% to 90%. An optical pickup device characterized by being provided. 2. A condensing optical system including a light source having an oscillation wavelength λ, and an objective lens for condensing a light beam emitted from the light source on an information recording surface via a transparent substrate of an optical information recording medium; An optical pickup device having a photodetector for receiving reflected light from the optical information recording medium, wherein a means for correcting a variation in spherical aberration is provided between the light source and the objective lens. The means for correcting the fluctuation of the spherical aberration is 0.2λrms.
An optical pickup device capable of correcting the spherical aberration up to 0.07λrms or less. 3. The means for correcting the fluctuation of the spherical aberration,
The optical pickup device according to claim 2, wherein spherical aberration up to 0.5? Rms can be corrected to 0.07? Rms or less. 4. A condensing optical system including a light source, an objective lens for converging a light beam emitted from the light source on an information recording surface via a transparent substrate of an optical information recording medium, and the optical information recording An optical pickup device having a photodetector for receiving reflected light from a medium, wherein a means for correcting a variation in spherical aberration generated in the objective lens is provided between the light source and the objective lens. An optical pickup device. 5. A light condensing optical system including a light source, an objective lens for converging a light beam emitted from the light source on an information recording surface via a transparent substrate of an optical information recording medium, and the optical information recording An optical pickup device having a photodetector for receiving reflected light from a medium, wherein the objective lens is disposed between the light source and the objective lens due to a minute variation in an oscillation wavelength of the light source. An optical pickup device, comprising: means for correcting a variation in generated spherical aberration. 6. A light condensing optical system including a light source, an objective lens for condensing a light beam emitted from the light source on an information recording surface via a transparent substrate of an optical information recording medium, and the optical information recording An optical pickup device having a photodetector for receiving reflected light from a medium, wherein a spherical surface generated between the light source and the objective lens in the condensing optical system due to a change in temperature and humidity. An optical pickup device comprising means for correcting a variation in aberration. 7. A light condensing optical system including a light source, an objective lens for converging a light beam emitted from the light source on an information recording surface via a transparent substrate of an optical information recording medium, and the optical information recording An optical pickup device having a photodetector for receiving reflected light from a medium, between the light source and the objective lens, due to minute fluctuations in the oscillation wavelength of the light source and changes in temperature and humidity. An optical pickup device comprising: means for correcting a variation in spherical aberration generated in the light-collecting optical system. 8. The means for correcting the fluctuation of the spherical aberration,
8. The image forming apparatus according to claim 1, further comprising at least one positive lens and at least one negative lens, at least one of which is a movable element that is movable in an optical axis direction.
An optical pickup device according to any one of the above. 9. The means for correcting the fluctuation of the spherical aberration,
It has a positive lens group including one positive lens and having a positive refractive power, and a negative lens group including one negative lens and having a negative refractive power, and at least one of the lens groups is arranged in the optical axis direction. The optical pickup device according to claim 1, wherein the optical pickup device is a movable element that can move. 10. The optical pickup device according to claim 8, wherein the means for correcting the fluctuation of the spherical aberration satisfies the following expression. νdP> νdN where νdP: average of Abbe numbers of d lines of all positive lenses including the positive lens νdN: average of Abbe numbers of d lines of all negative lenses including the negative lens 11. The optical pickup device according to claim 9, wherein the means for correcting the fluctuation of the spherical aberration satisfies the following expression. νdP> νdN where νdP: average of Abbe numbers of d lines of all positive lenses including the positive lens νdN: average of Abbe numbers of d lines of all negative lenses including the negative lens 12. The optical pickup device according to claim 10, wherein the νdP and the νdN satisfy the following expression. νdP> 55 νdN <35 13. The optical pickup device according to claim 11, wherein the νdP and the νdN satisfy the following expression. νdP> 55 νdN <35 14. When the means for correcting the fluctuation of the spherical aberration is composed of a positive lens group including the positive lens and a negative lens group including the negative lens, the following equation is satisfied. Item 13. The optical pickup device according to item 8, 10 or 12. Δd · │fP / fN│ / Δνd ≦ 0.05, where Δd: when recording or reproducing information on one information recording surface of any one optical information recording medium capable of recording or reproducing information. FP: focal length of the positive lens group (mm) (however, if the positive lens group has a diffractive surface, the total of refraction power and diffraction power) FN: focal length of the negative lens group (mm) (however, when the positive lens group has a diffractive surface, the total focal length including refraction power and diffraction power) Δνd: Difference between the maximum value of the Abbe number of the positive lens and the minimum value of the Abbe number of the negative lens in the positive lens group and the negative lens group 15. The apparatus according to claim 9, wherein said means for correcting the fluctuation of the spherical aberration satisfies the following equation.
Or the optical pickup device according to 13. Δd · │fP / fN│ / Δνd ≦ 0.05, where Δd: when recording or reproducing information on one information recording surface of any one optical information recording medium capable of recording or reproducing information. FP: focal length of the positive lens group (mm) (however, if the positive lens group has a diffractive surface, the total of refraction power and diffraction power) FN: focal length of the negative lens group (mm) (however, when the positive lens group has a diffractive surface, the total focal length including refraction power and diffraction power) Δνd: Difference between the maximum value of the Abbe number of the positive lens and the minimum value of the Abbe number of the negative lens in the positive lens group and the negative lens group 16. The optical pickup device is capable of recording and / or reproducing information on at least two types of optical information recording media, and the means for correcting the fluctuation of the spherical aberration includes a transparent substrate thickness. 13. The divergence of a light beam incident on the objective lens is changed for at least two types of optical information recording media different from each other according to the thickness of the transparent substrate. Optical pickup device. 17. The optical pickup device is capable of recording and / or reproducing information on at least two types of optical information recording media, and the means for correcting a variation in spherical aberration includes a transparent substrate thickness. 16. The divergence of a light beam incident on the objective lens is changed for at least two types of optical information recording media different from each other according to the thickness of each transparent substrate. An optical pickup device according to any one of the above. 18. The optical pickup device can record and / or reproduce information on and from an optical information recording medium in which a plurality of transparent substrates and information recording layers are sequentially stacked from the surface side of the optical information recording medium. Wherein the means for correcting the fluctuation of the spherical aberration changes the divergence of a light beam incident on the objective lens according to the information recording layer when condensing the information on each information recording layer. The optical pickup device according to claim 8, 10 or 12, wherein 19. The optical pickup device can record and / or reproduce information on an optical information recording medium in which a plurality of transparent substrates and information recording layers are sequentially stacked from the front side of the optical information recording medium. Wherein the means for correcting the fluctuation of the spherical aberration changes the divergence of a light beam incident on the objective lens according to the information recording layer when condensing the information on each information recording layer. An optical pickup device according to any one of claims 9, 11, 13 to 15. 20. When the transparent substrate thicknesses of the two types of optical information recording media are a and b (a <b), information is written on the information recording surface of the optical information recording medium having the transparent substrate thickness a. When recording or reproducing, the interval between the negative lens and the positive lens is increased as compared with when recording or reproducing information on the information recording surface of the optical information recording medium having the transparent substrate thickness b. The optical pickup device according to claim 16, wherein: 21. When the transparent substrate thicknesses of the two types of optical information recording media are a and b (a <b), information is recorded on the information recording surface of the optical information recording medium having the transparent substrate thickness a. When recording or reproducing, it is preferable to increase the distance between the negative lens group and the positive lens group than when recording or reproducing information on the information recording surface of the optical information recording medium having the transparent substrate thickness b. The optical pickup device according to claim 17, wherein: 22. When the means for correcting the variation of the spherical aberration comprises a positive lens group including the positive lens and a negative lens group including the negative lens, the following formula is satisfied. The optical pickup device according to 16, 18, or 20. | FP / fN | ≧ 1.3 where fP is the focal length of the positive lens group (however, if the positive lens group has a diffractive surface, the total focal length obtained by combining the refractive power and the diffractive power) Distance) fN: focal length of the negative lens group (when the negative lens group has a diffractive surface, the total focal length including refraction power and diffraction power) 23. The optical pickup device according to claim 17, wherein the following expression is satisfied. | FP / fN | ≧ 1.3 where fP is the focal length of the positive lens group (however, if the positive lens group has a diffractive surface, the total focal length obtained by combining the refractive power and the diffractive power) Distance) fN: focal length of the negative lens group (when the negative lens group has a diffractive surface, the total focal length including refraction power and diffraction power) 24. The optical pickup device according to claim 8, further comprising a shift device that shifts the movable element along an optical axis according to a change in spherical aberration. 25. The movable element according to claim 8, wherein the movable element is formed of a material having a specific gravity of 2.0 or less.
5. The optical pickup device according to any one of 4. 26. The optical pickup device according to claim 8, wherein at least one of the positive lens and the negative lens is formed of a plastic material. 27. The optical pickup device according to claim 8, wherein the movable element is formed of a plastic material. 28. The optical pickup device according to claim 8, wherein at least one of the positive lens and the negative lens has an aspheric surface on at least one surface. 29. The optical pickup device according to claim 27, wherein at least one surface of said movable element has an aspherical surface. 30. The light according to claim 8, wherein the means for correcting the fluctuation of the spherical aberration is made of a material having a saturated water absorption of 0.5% or less. Pickup device. 31. The means for correcting the fluctuation of the spherical aberration is made of a material having an internal transmittance of 85% or more at a thickness of 3 mm with respect to light having an oscillation wavelength of the light source. The optical pickup device according to any one of claims 8 to 30, wherein 32. The apparatus according to claim 8, wherein the means for correcting the fluctuation of the spherical aberration includes the one positive lens and the one negative lens. Optical pickup device. 33. The optical pickup according to claim 8, wherein the means for correcting the fluctuation of the spherical aberration includes an optical element having a diffraction surface having a ring-shaped diffraction structure. apparatus. 34. The optical pickup device according to claim 1, wherein the means for correcting the fluctuation of the spherical aberration includes an element capable of changing a refractive index distribution. 35. A condensing optical system including a light source, an objective lens for converging a light beam emitted from the light source onto a data recording surface via a transparent substrate of a data recording medium, and the optical information recording. An optical pickup device having a photodetector for receiving reflected light from a medium, wherein a fluctuation of spherical aberration generated by the objective lens and a change of spherical aberration generated by the objective lens are provided between the light source and the objective lens. An optical pickup device provided with means for correcting axial chromatic aberration. 36. The means for correcting the fluctuation of the spherical aberration and the axial chromatic aberration includes at least one positive lens and at least one negative lens, at least one of which is movable in the optical axis direction. The optical pickup device according to claim 35, wherein the optical pickup device is a movable element. 37. The means for correcting the fluctuation of the spherical aberration and the axial chromatic aberration includes a positive lens group including one positive lens and having a positive refractive power, and a negative lens including one negative lens. 36. The optical pickup device according to claim 35, further comprising a negative lens group having a force, wherein at least one of the lens groups is a movable element that is movable in an optical axis direction. 38. The optical pickup device according to claim 36, wherein the means for correcting the fluctuation of the spherical aberration and the axial chromatic aberration satisfies the following expression. νdP> νdN where νdP: average of Abbe numbers of d lines of all positive lenses including the positive lens νdN: average of Abbe numbers of d lines of all negative lenses including the negative lens 39. The optical pickup device according to claim 37, wherein the means for correcting the fluctuation of the spherical aberration and the axial chromatic aberration satisfies the following expression. νdP> νdN where νdP: average of Abbe numbers of d lines of all positive lenses including the positive lens νdN: average of Abbe numbers of d lines of all negative lenses including the negative lens 40. The optical pickup device according to claim 38, wherein the νdP and the νdN satisfy the following expression. νdP> 55 νdN <35 41. The optical pickup device according to claim 39, wherein the νdP and the νdN satisfy the following expression. νdP> 55 νdN <35 42. When the means for correcting the fluctuation of the spherical aberration and the axial chromatic aberration is constituted by a positive lens group including the positive lens and a negative lens group including the negative lens, the following equation is satisfied. The method according to claim 36, 38 or 4, wherein
The optical pickup device according to 0. Δd · │fP / fN│ / Δνd ≦ 0.05, where Δd: when recording or reproducing information on one information recording surface of any one optical information recording medium capable of recording or reproducing information. The amount of movement of the movable element (mm) fP: focal length of the positive lens group (mm) (provided that the diffractive surface is FN: focal length (mm) of the negative lens group (provided that the positive lens group has a diffractive surface) Δvd: difference between the maximum value of the Abbe number of the positive lens and the minimum value of the Abbe number of the negative lens in the positive lens group and the negative lens group. 43. The optical pickup device according to claim 37, wherein the means for correcting the fluctuation of the spherical aberration and the axial chromatic aberration satisfies the following equation. Δd · │fP / fN│ / Δνd ≦ 0.05, where Δd: when recording or reproducing information on one information recording surface of any one optical information recording medium capable of recording or reproducing information. FP: focal length of the positive lens group (mm) (however, if the positive lens group has a diffractive surface, the total of refraction power and diffraction power) FN: focal length of the negative lens group (mm) (however, when the positive lens group has a diffractive surface, the total focal length including refraction power and diffraction power) Δνd: Difference between the maximum value of the Abbe number of the positive lens and the minimum value of the Abbe number of the negative lens in the positive lens group and the negative lens group 44. When the means for correcting the fluctuation of the spherical aberration and the axial chromatic aberration is constituted by a positive lens group including the positive lens and a negative lens group including the negative lens, the following equation is satisfied. The method according to claim 36, 38 or 4, wherein
The optical pickup device according to 0. Δd · │fP / fN│ ≦ 0.50 where Δd is the value when recording or reproducing information on one information recording surface of any one optical information recording medium capable of recording or reproducing information. Movement amount of movable element (mm) fP: focal length of the positive lens group (mm) (however, if the positive lens group has a diffractive surface, the total focal point including refraction power and diffraction power) Distance) fN: Focal length (mm) of the negative lens group (however, if the positive lens group has a diffractive surface, the total focal length including refraction power and diffraction power) Δνd: Positive Difference between the maximum value of the Abbe number of the positive lens and the minimum value of the Abbe number of the negative lens in the lens group and the negative lens group. 45. The optical pickup device according to claim 37, wherein the means for correcting the variation of the spherical aberration and the axial chromatic aberration satisfies the following equation. . Δd · │fP / fN│ ≦ 0.50 where Δd is the value when recording or reproducing information on one information recording surface of any one optical information recording medium capable of recording or reproducing information. Movement amount of movable element (mm) fP: focal length of the positive lens group (mm) (however, if the positive lens group has a diffractive surface, the total focal point including refraction power and diffraction power) Distance) fN: Focal length (mm) of the negative lens group (however, if the positive lens group has a diffractive surface, the total focal length including refraction power and diffraction power) Δνd: Positive Difference between the maximum value of the Abbe number of the positive lens and the minimum value of the Abbe number of the negative lens in the lens group and the negative lens group. 46. The optical pickup device is capable of recording and / or reproducing information on at least two types of optical information recording media, and corrects the fluctuation of the spherical aberration and the axial chromatic aberration. For at least two types of optical information recording media having different transparent substrate thicknesses, depending on the respective transparent substrate thicknesses,
41. The optical pickup device according to claim 36, wherein the divergence of a light beam incident on the objective lens is changed. 47. The optical pickup device can record and / or reproduce information on at least two types of optical information recording media, and corrects the fluctuation of the spherical aberration and the axial chromatic aberration. For at least two types of optical information recording media having different transparent substrate thicknesses, depending on the respective transparent substrate thicknesses,
46. The optical pickup device according to claim 37, wherein the degree of divergence of a light beam incident on the objective lens is changed. 48. The optical pickup device can record and / or reproduce information on an optical information recording medium in which a plurality of transparent substrates and information recording layers are sequentially stacked from the front side of the optical information recording medium. Means for correcting the fluctuation of the spherical aberration and the axial chromatic aberration, according to the information recording layer when condensing the information on each information recording layer, the divergence of the light beam incident on the objective lens 36, 38, 38,
40. An optical pickup device according to 40. 49. The optical pickup device can record and / or reproduce information on an optical information recording medium in which a plurality of transparent substrates and information recording layers are sequentially stacked from the front side of the optical information recording medium. Means for correcting the fluctuation of the spherical aberration and the axial chromatic aberration, according to the information recording layer when condensing the information on each information recording layer, the divergence of the light beam incident on the objective lens Claims 37, 39, characterized in that
46. The optical pickup device according to any one of 41 to 45. 50. When the transparent substrate thicknesses of the two types of optical information recording media are a and b (a <b), information is written on the information recording surface of the optical information recording medium having the transparent substrate thickness a. When recording or reproducing, the interval between the negative lens and the positive lens is increased as compared with when recording or reproducing information on the information recording surface of the optical information recording medium having the transparent substrate thickness b. 47. The optical pickup device according to claim 46. 51. When the transparent substrate thicknesses of the two types of optical information recording media are a and b (a <b), information is written on the information recording surface of the optical information recording medium having the transparent substrate thickness a. When recording or reproducing, it is preferable to increase the distance between the negative lens group and the positive lens group than when recording or reproducing information on the information recording surface of the optical information recording medium having the transparent substrate thickness b. 48. The optical pickup device according to claim 47, wherein: 52. When the means for correcting the fluctuation of the spherical aberration and the axial chromatic aberration is constituted by a positive lens group including the positive lens and a negative lens group including the negative lens, the following expression is satisfied. 46. The method of claim 46, 48 or 50.
An optical pickup device according to item 1. | FP / fN | ≧ 1.3 where fP is the focal length of the positive lens group (however, if the positive lens group has a diffractive surface, the total focal length obtained by combining the refractive power and the diffractive power) Distance) fN: focal length of the negative lens group (when the negative lens group has a diffractive surface, the total focal length including refraction power and diffraction power) 53. The optical pickup device according to claim 47, wherein the following expression is satisfied. | FP / fN | ≧ 1.3 where fP is the focal length of the positive lens group (however, if the positive lens group has a diffractive surface, the total focal length obtained by combining the refractive power and the diffractive power) Distance) fN: focal length of the negative lens group (when the negative lens group has a diffractive surface, the total focal length including refraction power and diffraction power) 54. The optical pickup device according to claim 36, further comprising a shift device that shifts the movable element along an optical axis in accordance with a change in spherical aberration. 55. The optical pickup device according to claim 36, wherein the movable element is formed of a material having a specific gravity of 2.0 or less. 56. The optical pickup device according to claim 36, wherein at least one of the positive lens and the negative lens is formed of a plastic material. 57. The moving element according to claim 36, wherein the movable element is formed of a plastic material.
An optical pickup device according to any one of the above. 58. The optical pickup device according to claim 36, wherein at least one of the positive lens and the negative lens has an aspheric surface on at least one surface. 59. The optical pickup device according to claim 57, wherein at least one surface of the movable element has an aspherical surface. 60. The apparatus according to claim 36, wherein the means for correcting the fluctuation of the spherical aberration and the axial chromatic aberration is made of a material having a saturated water absorption of 0.5% or less. The optical pickup device according to any one of the above. 61. The means for correcting the fluctuation of the spherical aberration and the axial chromatic aberration is formed of a material having an internal transmittance of 85% or more at a thickness of 3 mm with respect to light having an oscillation wavelength of the light source. The optical pickup device according to any one of claims 36 to 60, wherein: 62. The apparatus according to claim 36, wherein the means for correcting the variation of the spherical aberration and the axial chromatic aberration includes the one positive lens and the one negative lens.
62. The optical pickup device according to any one of items 61 to 61. 63. The apparatus according to claim 36, wherein the means for correcting the fluctuation of the spherical aberration and the axial chromatic aberration includes an optical element having a diffraction surface having a ring-shaped diffraction structure. An optical pickup device as described in Crab. 64. The optical pickup device according to claim 35, wherein the means for correcting the fluctuation of the spherical aberration and the axial chromatic aberration includes an element capable of changing a refractive index distribution. 65. The apparatus according to claim 64, wherein the means for correcting the fluctuation of the spherical aberration and the axial chromatic aberration includes a coupling lens having a function of correcting the axial chromatic aberration of the objective lens. An optical pickup device as described in the above. 66. An optical element having a diffraction surface having an annular diffraction structure.
6. The optical pickup device according to any one of 5. 67. The optical pickup device according to claim 66, wherein said objective lens is said optical element. 68. The optical pickup device according to claim 67, wherein the objective lens is a single objective lens having at least one aspheric surface and satisfies the following expression. 5.0 ≦ fD / f ≦ 40.0 where fD is the diffraction structure of the objective lens, Φb = b ₂ h ² +
b ₄ h ⁴ + b ₆ h ⁶ +... (where h is the height (mm) from the optical axis,
When b ₂ , b ₄ , b ₆ ,... are second-order, fourth-order, sixth-order,..., optical path difference function coefficients, fD = 1 / (− 2 ·
b ₂₎ is defined by the focal length at the oscillation wavelength of only by the light source the diffractive structure of the objective lens f: the objective a combination of the diffraction power by the diffractive structure of the the refractive power of the objective lens objective lens Focal length of the entire lens at the oscillation wavelength of the light source 69. The diffractive structure, the diffracted light generated by the diffractive structure, the n-th order diffracted light of a diffracted light amount larger than the diffracted light amount of any other order diffracted light (here,
n is an integer other than -1, 0, and +1), and the n-th order diffracted light is used for recording and / or reproducing information on the optical information recording medium. The optical pickup device according to any one of claims 33, 63, 66 to 68, wherein light can be collected on an information recording surface of a medium. 70. An optical element having a diffractive surface having a ring-shaped diffractive structure, wherein the means for correcting the fluctuation of the spherical aberration is such that each positive lens including the positive lens has an Abbe number of 70. The optical pickup device according to any one of claims 8 to 33, wherein the Abbe number of each of the negative lenses including the negative lens is 0 or less or 40.0 or more. 71. An optical element having a diffractive surface having a ring-shaped diffractive structure, wherein the means for correcting the fluctuation of the spherical aberration and the axial chromatic aberration includes: 4. The Abbe number of the negative lens is not more than 70.0, or the Abbe number of all negative lenses including the negative lens is 40.0 or more.
64. The optical pickup device according to any one of 6 to 63. 72. The means for correcting the fluctuation of the spherical aberration, wherein the paraxial power at the oscillation wavelength of the light source is P1, the paraxial power at a wavelength shorter by 10 nm than the oscillation wavelength is P2, and the paraxial power is 10 nm longer than the oscillation wavelength. 71. The optical pickup device according to claim 70, wherein when the paraxial power at the wavelength is P3, the following expression is satisfied. P2 <P1 <P3 73. A means for correcting the fluctuation of the spherical aberration and the axial chromatic aberration, wherein the paraxial power at an oscillation wavelength of the light source is P1, the paraxial power at a wavelength shorter by 10 nm than the oscillation wavelength is P2, 10 from the oscillation wavelength
72. The optical pickup device according to claim 71, wherein when the paraxial power at a wavelength longer by nm is P3, the following expression is satisfied. P2 <P1 <P3 74. The diffractive surface has a function of suppressing axial chromatic aberration generated by the objective lens with respect to minute fluctuations in the oscillation wavelength of the light source.
73. The optical pickup device according to any one of 3, 63, 66 to 73. 75. The diffractive surface has a wavelength characteristic such that the back focus of the objective lens becomes shorter when the oscillation wavelength of the light source slightly fluctuates to a longer wavelength side. 63. The optical pickup device according to any one of 63, 66 to 74. 76. The diffractive surface has a spherical aberration characteristic that changes when the oscillation wavelength of the light source slightly fluctuates to a longer wavelength side such that the spherical aberration of the objective lens is insufficiently corrected. The optical pickup device according to any one of claims 33, 63, and 66 to 75. 77. The light source has at least two light sources: a light source having an oscillation wavelength λ1 and a light source having an oscillation wavelength λ2 (λ1 <λ2); First
With respect to the information recording surface of the first optical information recording medium having the thickness t1 of the transparent substrate, with a wavefront aberration of 0.07λ within a predetermined numerical aperture on the image side of the objective lens required for recording or reproducing information.
The second light flux emitted from the light source having the oscillation wavelength λ2 can be condensed in a state of 1 rms or less, and is converted into a transparent substrate thickness t2 (t1
≤ t2) The light is focused on the information recording surface of the second optical information recording medium with a wavefront aberration of 0.07λ2 rms or less within a predetermined numerical aperture on the image side of the objective lens required for recording or reproducing information. The optical pickup device according to any one of claims 1 to 65, wherein the optical pickup device can be used. 78. The optical pickup device according to claim 77, further comprising an optical element having a diffraction surface having a ring-shaped diffraction structure. 79. The diffractive surface of the optical element transmits the first light flux emitted from the light source having the oscillation wavelength λ1 to an information recording surface of a first optical information recording medium having a transparent substrate thickness t1. The laser beam can be focused with a wavefront aberration of 0.07λ1 rms or less within a predetermined numerical aperture on the image side of the objective lens required for recording or reproducing information, and emitted from a light source having the oscillation wavelength λ2 (λ1 <λ2) The second luminous flux is converted to a transparent substrate thickness t2.
With respect to the information recording surface of the second optical information recording medium (t1 ≦ t2), the wavefront aberration is 0.07λ2 rms or less within a predetermined numerical aperture on the image side of the objective lens required for recording or reproducing information. The optical pickup device according to claim 78, wherein the optical pickup device has a wavelength characteristic capable of condensing light. 80. An image of the objective lens necessary for recording or reproducing information on the information recording surface of the first optical information recording medium using the first light beam emitted from the light source having the oscillation wavelength λ1. The predetermined numerical aperture on the side
With respect to the information recording surface of the information recording medium,
When a predetermined numerical aperture on the image side of the objective lens required for recording or reproducing information by the second light flux emitted from the second light source is NA2 (NA1> NA2), the diffraction surface of the optical element is Converging the second light flux emitted from the light source having the oscillation wavelength λ2 on the information recording surface of the second optical information recording medium in the NA1 with a wavefront aberration of 0.07λ2 rms or more. The optical pickup device according to claim 79, wherein: 81. The optical pickup device according to claim 78, wherein the objective lens is the optical element. 82. The optical pickup device according to claim 81, wherein the objective lens is a single lens having at least one aspheric surface and satisfies the following expression. 0.5 ≦ (f1 / νd) · fD1 ≦ 10.0 where f1: at the oscillation wavelength λ1 of the entire objective lens obtained by combining the refraction power of the objective lens and the diffraction power of the objective lens by the diffraction structure. Focal length (mm) νd: Abbe number of d-line of the objective lens fD1: Φb = b ₂ h ^{2 for the} diffraction structure of the objective lens
+ B ₄ h ⁴ + b ₆ h ⁶ +... (Where h is the height (mm) from the optical axis and b ₂ , b ₄ , b ₆ ,...) … Is the second, fourth, sixth, etc.
..), FD = 1 / (− 2 ·
b ₂ ), the focal length at the oscillation wavelength λ1 due to only the diffractive structure of the objective lens (m
m) 83. The optical pickup device according to claim 81, wherein the objective lens is a single objective lens having at least one aspheric surface and satisfies the following expression. −25.0 ≦ (b ₂ /λ1)≦0.0, where b _{2 represents the} diffraction structure of the objective lens as φb = b ₂ h ² +
b ₄ h ⁴ + b ₆ h ⁶ +... (where h is the height (mm) from the optical axis,
b ₂ , b ₄ , b ₆ ,... are second-order, fourth-order, sixth-order,..., second-order optical path difference function coefficients, and λ1: the oscillation wavelength λ1 ( mm) 84. The diffractive surface has a function of correcting axial chromatic aberration generated by the objective lens with respect to minute fluctuations in the oscillation wavelength of the light source.
84. The optical pickup device according to any one of the above items. 85. The diffractive surface has a wavelength characteristic such that the back focus of the objective lens is shortened when the oscillation wavelength of the light source slightly fluctuates to a longer wavelength side. 84. The optical pickup device according to any one of items 84. 86. The diffractive surface has a spherical aberration characteristic that changes when the oscillation wavelength of the light source slightly fluctuates to a longer wavelength side so that the spherical aberration of the objective lens is insufficiently corrected. The optical pickup device according to any one of claims 78 to 85, characterized in that: 87. at least a first portion on at least one surface of the objective lens, which divides a light beam emitted from the light source by a refraction action into a plurality of light beams in order from an optical axis side to an outer periphery thereof; A second portion and a third portion, wherein the first portion and the third portion have a transparent substrate thickness t1.
A light beam from the light source can be collected so that information can be recorded or reproduced on an information recording surface of the first optical information recording medium; the first portion and the second portion; Is the transparent substrate thickness t2
The light beam from the light source can be collected so that information can be recorded or reproduced on the information recording surface of the second optical information recording medium (t1 <t2). 65. The optical pickup device according to any one of 1 to 65. 88. at least a first portion, wherein the objective lens divides a light beam emitted from the light source into a plurality of light beams by a refraction action on at least one surface in order from an optical axis side to an outer periphery thereof; It has a second part and a third part, and the first part and the third part record or reproduce information on or from an information recording surface of the first optical information recording medium. The first part and the second part record information on an information recording surface of the second optical information recording medium. The optical pickup device according to claim 77, wherein a light beam from the light source having the oscillation wavelength λ2 can be collected so that reproduction can be performed. 89. At least one surface of the objective lens,
By the refraction action, the incident light beam is converted into k (k ≧ 4) annular light beams (here, in order from the optical axis side to the outside thereof, the first, second,..., K-th light beams). In the case where information is recorded and / or reproduced on the first optical information recording medium, the best image plane position formed by the first and k-th light beams is formed. The spherical aberration component of the wavefront aberration of the first and k-th light beams at 0.0 is 0.0
5λ1 rms or less (the wavelength of the light source of λ1), and at least 2 out of the second to (k−1) th light fluxes
Each of the two light beams has an apparent best image plane position formed at a position different from the best image surface position formed by the first and k-th light beams, and the best image surface position formed by the first and k-th light beams The wavefront aberration of the light beam in each of the first to k-th light beams passing through the required numerical aperture with respect to the first optical information recording medium is substantially miλ1 (where mi is an integer, i = 1, 2,.・
78. The optical pickup device according to claim 77, wherein: k). 90. A transparent substrate thickness t1 of the first optical information recording medium is 0.6 mm or less, a transparent substrate thickness t2 of the second optical information recording medium is 0.6 mm or more, 90. The oscillation wavelength λ2 is in a range of 600 nm or more and 800 nm or less.
90. The optical pickup device according to any one of items 8 and 89. 91. Among the spherical aberration of the objective lens, 3
The optical pickup according to any one of claims 1 to 90, wherein the following equation is satisfied, where SA1 is the next spherical aberration component, and SA2 is the sum of the fifth, seventh, and ninth order spherical aberration components. apparatus. | SA1 / SA2 |> 1.0 where SA1: third-order spherical aberration component when the aberration function is expanded to a Zernike polynomial SA2: 5 when the aberration function is expanded to a Zernike polynomial Square root of the sum of squares of the next-order spherical aberration component, the seventh-order spherical aberration component, and the ninth-order spherical aberration component 92. The stop for determining the numerical aperture of the objective lens is located on the side where the optical information recording medium is arranged from the surface apex of the surface closest to the light source of the objective lens. 90. The optical pickup device according to any one of 1 to 91. 93. The optical pickup device according to claim 1, wherein the objective lens is a single lens having at least one aspheric surface. 94. The optical pickup device according to claim 1, wherein the light source has a light source having an oscillation wavelength of at least 500 nm or less. 95. The image-side numerical aperture NA of the objective lens is:
The optical pickup device according to any one of claims 1 to 94, wherein the optical pickup device is at least 0.65 or more. 96. The optical pickup device according to claim 1, wherein the objective lens satisfies the following expression. 1.1 ≦ d1 / f ≦ 3.0, where d1: axial lens thickness (mm) f: focal length (mm) at the oscillation wavelength of the light source (provided that the light source has a plurality of light sources having different oscillation wavelengths) In that case, the focal length at the shortest oscillation wavelength,
If the objective lens has a diffractive surface, the total focal length including the refracting power and the diffracting power) 97. The object lens according to claim 1, wherein the objective lens is formed of a plastic material.
An optical pickup device according to any one of the above. 98. The objective lens, wherein the objective lens has a saturated water absorption of 0.5.
The optical pickup device according to any one of claims 1 to 97, wherein the optical pickup device is formed of a material having a content of 5% or less. 99. The objective lens has an internal transmittance of 85 mm at a thickness of 3 mm with respect to light having an oscillation wavelength of the light source.
The optical pickup device according to any one of claims 1 to 98, wherein the optical pickup device is formed of a material having a percentage of at least 100%. 100. An objective lens applicable to the optical pickup device according to any one of claims 1 to 99. 101. An objective lens which is the objective lens used in the optical pickup device according to any one of claims 1 to 99. 102. An optical pickup device capable of recording and / or reproducing information on at least two kinds of optical information recording media, comprising: a light source having an oscillation wavelength λ1; and an oscillation wavelength λ2 different from the oscillation wavelength λ1. (Λ1 <λ2) and a first light beam emitted from the light source having the oscillation wavelength λ1 is condensed on the information recording surface of the first optical information recording medium via a transparent substrate having a transparent substrate thickness t1. At the same time, the second light flux emitted from the light source having the oscillation wavelength λ2 is focused on the information recording surface of the second optical information recording medium via the transparent substrate having a transparent substrate thickness t2 (t1 ≦ t2). In an objective lens for an optical pickup device having a condensing optical system including an objective lens and a photodetector receiving reflected light from the first and second optical information recording media, it is preferable that the following expression is satisfied. Objective lens featured. 1.1 ≦ d1 / f ≦ 3.0 where, d1: on-axis lens thickness (mm) f: focal length (mm) at the oscillation wavelength λ1 (however, when the objective lens has a diffraction surface, , Total focal length including refraction power and diffraction power) 103. The objective lens according to claim 102, wherein the image-side numerical aperture NA is 0.75 or more. 104. The objective lens according to claim 102, further comprising a diffraction surface having a ring-shaped diffraction structure. 105. The diffractive surface is used for recording or reproducing information on the information recording surface of the first optical information recording medium with the first light flux emitted from the light source having the oscillation wavelength λ1. The second light flux emitted from the light source having the oscillation wavelength λ2 can be collected within a predetermined numerical aperture on the image side of the objective lens with a wavefront aberration of 0.07λ1 rms or less. Characterized by having a wavelength characteristic such that light can be collected with a wavefront aberration of 0.07λ2 rms or less within a predetermined numerical aperture on the image side of the objective lens required for recording or reproducing information on the information recording surface. Claim 1
The objective lens according to 04. 106. An image of the objective lens required for recording or reproducing information on the information recording surface of the first optical information recording medium using the first light beam emitted from the light source having the oscillation wavelength λ1. The predetermined numerical aperture on the side is NA1, and the objective necessary for recording or reproducing information on the information recording surface of the second information recording medium by the second light flux emitted from the light source of the oscillation wavelength λ2. When the predetermined numerical aperture on the image side of the lens is NA2 (NA1> NA2), the diffractive surface converts the second light flux emitted from the light source having the oscillation wavelength λ2 into the second optical information recording medium. Wavefront aberration 0.07λ2rm within NA1 with respect to the information recording surface
11. The light is condensed in a state of s or more.
105. The objective lens according to 4 or 105. 107. The objective lens according to claim 104, wherein the diffractive surface has a function of suppressing axial chromatic aberration with respect to a minute change in the oscillation wavelength of the light source. 108. The diffractive surface has a wavelength characteristic that shortens the back focus of the objective lens when the oscillation wavelength of the light source slightly fluctuates to a longer wavelength side. The objective lens according to any one of the above. 109. The diffractive surface has a spherical aberration characteristic that changes when the oscillation wavelength of the light source slightly fluctuates to a longer wavelength side such that the spherical aberration of the objective lens is insufficiently corrected. The objective lens according to any one of claims 104 to 108. 110. A single lens having at least one aspheric surface, wherein the following expression is satisfied.
The objective lens according to any one of 2 to 109. 0.5 ≦ (f1 / νd) · fD1 ≦ 10.0 where f1: focal length (mm) at the oscillation wavelength λ1 obtained by combining the refraction power and the diffraction power by the diffraction structure. Νd: d-line of the lens material Abbe number fD1: Φb = b ₂ h ² + b ₄ h ⁴ + b ₆ h ⁶
+ ……… (where h is the height (mm) from the optical axis and b ₂ , b ₄ , b
_6, ......... secondary, fourth, sixth, an optical path difference function coefficients of .........) time, fD = 1 / (- 2 · b 2) is defined by, the only by the diffractive structure Focal length at oscillation wavelength λ1 (mm) 111. A single lens having at least one aspheric surface, wherein the following expression is satisfied.
The objective lens according to any one of 2 to 109. −25.0 ≦ (b ₂ /λ1)≦0.0, where b ₂ : Φb = b ₂ h ² + b ₄ h ⁴ + b ₆ h ⁶ +
……… expressed by the optical path difference function (where,
h is the height (mm) from the optical axis, and b ₂ , b ₄ , b ₆ ,
... Are the second-order, fourth-order, sixth-order,..., Second-order optical path difference function coefficients.) Λ1: The oscillation wavelength λ1 (mm) 112. The following equation is satisfied when the third-order spherical aberration component among the spherical aberrations is SA1, and the sum of the fifth-order, seventh-order, and ninth-order spherical aberration components is SA2. The objective lens according to any one of items 102 to 111. | SA1 / SA2 |> 1.0 where SA1: third-order spherical aberration component when the aberration function is expanded to a Zernike polynomial SA2: 5 when the aberration function is expanded to a Zernike polynomial Square root of the sum of squares of the next-order spherical aberration component, the seventh-order spherical aberration component, and the ninth-order spherical aberration component 113. at least a first part, a second part, and at least one surface, which divides a light beam emitted from the light source into a plurality of light beams by refraction in order from an optical axis side to an outer periphery thereof; A third portion, wherein the first portion and the third portion are provided with the oscillation portion so that information can be recorded or reproduced on an information recording surface of the first optical information recording medium. The first part and the second part record or reproduce information on or from an information recording surface of the second optical information recording medium. 102. A light beam from a light source having the oscillation wavelength λ2 can be condensed so that the light beam can be emitted.
Or the objective lens according to 103; 114. At least one surface is provided with k (k ≧ 4) annular luminous fluxes (here, first, second,...・ ・
.., A k-th light beam), and forming and / or reproducing information on / from the first optical information recording medium. The spherical aberration component of the wavefront aberration of the first and k-th light beams at the best image plane position created by the k-light beam is 0.0
5λ1 rms or less (the wavelength of the light source of λ1), and at least 2 out of the second to (k−1) th light fluxes
Each of the two light beams has an apparent best image plane position formed at a position different from the best image surface position formed by the first and k-th light beams, and the best image surface position formed by the first and k-th light beams The wavefront aberration of the light beam in each of the first to k-th light beams passing through the required numerical aperture with respect to the first optical information recording medium is substantially miλ1 (where mi is an integer, i = 1, 2,.・
..., k), the objective lens according to claim 102 or 103. 115. The objective lens according to claim 102, wherein the objective lens is formed of a plastic material. 116. The objective lens according to claim 102, wherein the objective lens is formed of a material having a saturated water absorption of 0.5% or less. 117. The light emitting device according to claim 102, wherein the light source is formed of a material having an internal transmittance of 85% or more at a thickness of 3 mm with respect to the oscillation wavelength of the light source.
7. The objective lens according to any one of 6. 118. A lens according to claim 102, wherein at least one surface is an aspherical single lens.
The objective lens according to any one of the above. The objective lens according to any one of claims 102 to 118, which is applicable to the optical pickup device according to any one of claims 1 to 99. 120. An all positive lens including at least one positive lens and at least one negative lens, at least one of which is a movable element movable along the optical axis direction, and including the positive lens. Abbe number of each is 7
A beam expander characterized by having an Abbe number of 0.0 or less or a total Abbe number of all negative lenses including the negative lens of 40.0 or more, and having at least one surface having a diffraction surface having an annular diffraction structure. 121. A paraxial power at an oscillation wavelength of a light source that outputs a light beam to be incident is P1, a paraxial power at a wavelength shorter by 10 nm than the oscillation wavelength is P2, and a paraxial power at a wavelength longer by 10 nm than the oscillation wavelength is P1. The beam expander according to claim 120, wherein when P3 is satisfied, the following expression is satisfied. P2 <P1 <P3 122. The diffractive surface has a function of suppressing axial chromatic aberration generated by a converging lens disposed on an emission side with respect to a minute fluctuation of an oscillation wavelength of a light source that outputs a light beam to be incident. A beam expander according to claim 120 or claim 121. 123. The diffractive surface, when the oscillation wavelength of a light source that outputs a light beam to be incident slightly fluctuates to a longer wavelength side,
The beam expander according to any one of claims 120 to 122, wherein the beam expander has a wavelength characteristic such that the back focus of the condenser lens disposed on the emission side is shortened. 124. When the oscillation wavelength of a light source that outputs a light beam to be incident fluctuates slightly to a longer wavelength side,
The beam expander according to any one of claims 120 to 123, wherein the beam expander has a spherical aberration characteristic that changes in a direction such that the spherical aberration of the condenser lens disposed on the emission side is insufficiently corrected. 125. The movable element is made of a material having a specific gravity of 2.0 or less.
125. The beam expander according to any one of to 124. 126. The beam expander according to claim 120, wherein the movable element is formed from a plastic material. The at least one movable element has an aspherical surface on at least one surface thereof.
The beam expander according to any one of the above. 128. The movable element has a saturated water absorption of 0.1.
130. The beam expander according to any one of claims 120 to 127, wherein the beam expander is made of a material having a content of 5% or less. 129. The movable element is made of a material having an internal transmittance of 85% or more at a thickness of 3 mm with respect to light having an oscillation wavelength of a light source to be incident, wherein the movable element is formed of a material. 128. The beam expander according to any of 128. 130. The beam expander according to claim 120, wherein the beam expander is made of a plastic material. 131. The beam expander according to claim 120, wherein at least one surface has an aspherical surface. 132. The beam expander according to claim 120, wherein the beam expander is made of a material having a saturated water absorption of 0.5% or less. 133. The light-emitting device is made of a material having an internal transmittance of 85% or more at a thickness of 3 mm with respect to light having an oscillation wavelength of a light source to be incident.
133. The beam expander according to any one of 0 to 124 and 130 to 132. A beam expander according to any one of claims 120 to 133, which is applicable to the optical pickup device according to any one of claims 8 to 33 and 36 to 63.