JP2011034673A - Optical pickup device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical pickup device and an optical system for effectively correcting a variation of spherical aberration caused by the mode hopping of a semiconductor laser. <P>SOLUTION: A means (negative lens 4) for correcting the variation of spherical aberration generated in an objective lens 3 is prepared between a light source 11 as a semiconductor laser and the objective lens 3. Even if a mode hopping phenomenon occurs in the semiconductor laser 11 to change an oscillation wavelength, the resulting variation of the spherical aberration of the objective lens 3 is effectively prevented. Even if the refraction index of the objective lens 3 is changed due to a change in an ambient temperature or humidity, the resulting variation of the spherical aberration of the objective lens 3 can be effectively prevented. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  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 variations in spherical aberration.

  In recent years, along with the practical application of short-wavelength red semiconductor lasers, DVDs (digital versatile discs), which are high-density optical discs with the same size and capacity as conventional optical discs, ie, CDs (compact discs) that are optical information recording media ) Is under development, but it is expected that next-generation optical discs with higher density will appear in the near future. In an optical system of an optical information recording / reproducing apparatus using such an optical disc as a medium, the recording signal is condensed on the recording medium via an objective lens in order to increase the recording signal density or to reproduce the high-density recording signal. It is required to reduce the spot diameter. For this purpose, there is a fact that the wavelength of the laser as the light source is being shortened and the NA of the objective lens is being increased.

  By the way, when the laser wavelength is shortened and the objective lens has a high NA, a relatively long wavelength laser that records or reproduces information on a conventional optical disk such as a CD or a DVD. In an optical pickup device composed of a combination of a low NA of an objective lens, even a problem that can be almost ignored becomes more obvious.

One of them is a problem of axial chromatic aberration that occurs in the objective lens due to minute fluctuations in the oscillation wavelength of the laser light source. The refractive index change due to the minute fluctuation of the wavelength of a general optical lens material increases as the short wavelength is handled. For this reason, the defocus amount of the focus caused by minute fluctuations in wavelength increases. However, the depth of focus of the objective lens is expressed by k · 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, the smaller the depth of focus, and a slight defocus amount 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, In order to prevent deterioration of wavefront aberration due to high frequency superposition, correction of axial chromatic aberration is important.

  Furthermore, another problem that becomes apparent in the combination of shortening the wavelength of the laser and increasing the NA of the objective lens is the fluctuation of the spherical aberration of the optical system due to temperature and humidity changes. That is, the plastic lens generally used in the optical pickup device is easily deformed by changes in temperature and humidity, and the refractive index changes accordingly. Even if the spherical aberration fluctuates due to a change in refractive index, 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, next-generation optical discs that require a combination of shorter laser wavelengths and higher NA objective lenses for information recording or reproduction, and conventional optical discs, as described above, include the light source wavelength and objective lens. NA is very different. In addition, it is effective to reduce the thickness of the transparent substrate in order to suppress coma aberration, which is largely caused by the inclination of the disk surface from the plane perpendicular to the optical axis expected in the next generation optical disk. However, 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, the spherical aberration can be suppressed with respect to different optical information recording media including a next-generation optical disc by using a compact optical pickup device without significantly increasing the cost. The problem is whether to record or reproduce information.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an optical pickup device, an objective lens, and a beam expander that can effectively correct fluctuations in spherical aberration of the objective lens caused by temperature and humidity changes.

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

  It is another object of the present invention to provide an optical pickup device that includes a short wavelength laser and a high NA objective lens and can record or reproduce information on different optical information recording media.

  The optical pickup device according to claim 1 includes a light source and a condensing optical system including 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. And an optical pickup device for receiving reflected light from the optical information recording medium, wherein the objective lens includes at least one lens made of a plastic material, the light source and the Changes in at least one of the shape and refractive index of the objective lens and fluctuations in the oscillation wavelength of the light source with respect to an environmental change between a temperature of −30 ° C. to + 85 ° C. and a humidity of 5% to 90% between the objective lens and the objective lens Since the means for correcting the fluctuation of spherical aberration caused by the optical pickup device is provided, the objective lens seems to have a refractive index change according to the temperature and humidity changes in the environment where the optical pickup device is used. Even if, or even when the oscillation wavelength variation of the light source occurs, the fluctuation of spherical aberration of the objective lens due to them, effectively it is possible to suppress.

  The space between the light source and the objective lens includes the objective lens. Therefore, even a diffractive surface provided on the surface of the objective lens can be a means for correcting the variation of the spherical aberration of the present invention.

The optical pickup device according to claim 2 includes 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 condensing optical system and a photodetector for receiving reflected light from the optical information recording medium,
Provided between the light source and the objective lens is a means for correcting the variation of spherical aberration,
The means for correcting the fluctuation of the spherical aberration can correct the spherical aberration up to 0.2λ rms to 0.07λ rms or less. For example, the temperature and humidity change of the environment where the optical pickup device is used and / or the oscillation of the light source Variations in spherical aberration of the objective lens caused by minute variations in wavelength can be effectively suppressed.

  In the optical pickup device according to claim 3, it is preferable that the means for correcting the fluctuation of the spherical aberration can correct the spherical aberration up to 0.5λrms to 0.07λrms or less.

  5. An optical pickup device according to claim 4, comprising 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. And a photodetector for receiving reflected light from the optical information recording medium, wherein a variation in spherical aberration generated in the objective lens between the light source and the objective lens For example, the variation of the spherical aberration of the objective lens caused by, for example, a change in the temperature and humidity of the environment in which the optical pickup device is used and / or a slight variation in the oscillation wavelength of the light source is effectively suppressed. be able to.

  Since the oscillation wavelength of the semiconductor laser has an individual variation of about ± 10 nm, in an optical system using a short wavelength light source and an objective lens having a high image side numerical aperture, a semiconductor laser shifted from a reference wavelength is used. If it is used, it causes degradation of the performance of the apparatus, and it may be necessary to select a semiconductor laser. 6. An optical pickup apparatus according to claim 5, wherein the optical pickup device includes a light source 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. And a light detector for receiving reflected light from the optical information recording medium, the optical pickup device being caused by minute fluctuations in the oscillation wavelength of the light source between the light source and the objective lens Since the means for correcting the fluctuation of the spherical aberration generated in the objective lens is provided, the fluctuation of the spherical aberration of the objective lens that occurs when the semiconductor laser deviated from the reference wavelength is used is effectively suppressed. Therefore, it is not necessary to select a semiconductor laser.

  7. An optical pickup device according to claim 6, comprising 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. And a light detector for receiving reflected light from the optical information recording medium, wherein the light condensing occurs between the light source and the objective lens due to a change in temperature and humidity. Since the means for correcting the fluctuation of spherical aberration generated in the optical system is provided, for example, the fluctuation of spherical aberration of the objective lens caused by the change in the temperature and humidity of the environment where the optical pickup device is used is effectively suppressed. I can do it.

  8. An optical pickup device according to claim 7, comprising 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. And an optical pickup device for receiving reflected light from the optical information recording medium, wherein a minute fluctuation in the oscillation wavelength of the light source and a temperature are interposed between the light source and the objective lens. Since means for correcting the variation of spherical aberration generated in the condensing optical system due to humidity change is provided, for example, according to the temperature and humidity change of the environment where the optical pickup device is used, and as a reference as the light source Variations in spherical aberration of the objective lens that occur when a semiconductor laser deviating from the wavelength is used can be effectively suppressed.

  9. The optical pickup device according to claim 8, wherein 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 can be shifted in the optical axis direction. It is a movable element. Further, in the optical pickup device according to claim 9, the means for correcting the fluctuation of the spherical aberration includes a positive lens group including one positive lens and having positive refractive power, and a negative lens including one negative lens. A negative lens group having a refractive power of at least one lens group, and at least one of the lens groups is a movable element capable of shifting in the optical axis direction.

  In the optical pickup device used for the short wavelength light source, as described above, the variation of the spherical aberration due to the wavelength variation of the light source and the temperature / humidity variation 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 light source with a short wavelength, it is necessary to provide means for correcting the variation of these spherical aberrations. If the spherical aberration of the objective lens fluctuates due to minute fluctuations in the oscillation wavelength of the light source or changes in temperature and humidity, the movable element of the means for correcting the fluctuation of the spherical aberration is moved by an appropriate amount to By changing the 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 variation of the spherical aberration can be corrected.

The optical pickup device according to claims 10 and 11 is characterized in that the means for correcting the variation of the spherical aberration satisfies the following expression.
νdP> νdN (1)
However,
νdP: Average d-line Abbe number of all positive lenses including the positive lens νdN: Average d-line Abbe number of all negative lenses including the negative lens The above equation (1) relates to correction of axial chromatic aberration. When spherical aberration of the objective lens fluctuates due to minute fluctuations in the oscillation wavelength of the light source, changes in temperature and humidity, etc., means for correcting this, for example, using an optical element capable of shifting 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 so that the spherical aberration of the objective lens is minimized. The axial chromatic aberration of the objective lens, which is a problem when using a short wavelength light source, can be corrected by configuring the means for correcting the variation 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 variation of the spherical aberration so as to satisfy the above equation (1), chromatic aberration having a polarity opposite to that of the chromatic aberration generated in the objective lens can be generated. it can. Accordingly, since the axial chromatic aberration cancels out, the wavefront transmitted through the means for correcting 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. If a diffractive surface is added to the objective lens and / or means for correcting fluctuations of the spherical aberration, and the diffractive lens is such that the back focus of the objective lens is shortened on the long wavelength side, the aberration can be corrected better. Is possible. In this case, since 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, the means for correcting the variation of the spherical aberration is, for example, an optical that can be shifted in the optical axis direction. When configured using elements, the stroke of such optical elements can be small.

  Furthermore, the power of the diffractive surface can be reduced by sharing the role of axial chromatic aberration correction with the means for correcting the variation of the spherical aberration and the diffractive surface, thereby increasing the distance between the diffracting ring zones. This makes it easy to manufacture a diffractive lens having high diffraction efficiency. Accordingly, the spherical aberration of the entire optical system and the shaft can be obtained even when a wavelength variation or a temperature / humidity change occurs without separately providing a means for correcting the variation of the spherical aberration and a means for correcting the axial chromatic aberration. A compact optical pickup device in which the upper chromatic aberration is corrected well can be obtained.

The optical pickup device according to claims 12 and 13 is characterized in that the νdP and the νdN satisfy the following expressions.
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 expressions (2) and (3), chromatic aberration having a polarity opposite to that of the objective lens can be generated. The axial chromatic aberration of the optical pickup optical system can be corrected well.

In the optical pickup device according to claim 14, when the means for correcting the variation of the spherical aberration includes a positive lens group including the positive lens and a negative lens group including the negative lens, the following expression is established. The optical pickup apparatus according to claim 15 is characterized in that the means for correcting the variation of the spherical aberration satisfies the following expression.
Δd · | fP / fN | /Δνd≦0.05 (4)
However,
Δd: Amount of movement (mm) of the movable element when information is recorded or reproduced on one information recording surface of any one optical information recording medium capable of recording or reproducing information
fP: focal length (mm) of the positive lens group (however, when the positive lens group is provided with a diffractive surface, the total focal length combining the refractive power and the diffractive power)
fN: focal length (mm) of the negative lens group (however, when the positive lens group is provided with a diffractive surface, the total focal length combining the refractive power and the diffractive 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) is the correction amount of the longitudinal chromatic aberration of the objective lens. Further, the present invention relates to a balance between 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. 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 satisfactorily, and the objective lens caused by the wavelength variation or temperature / humidity change of the light source When the means for correcting the fluctuation of the spherical aberration is configured using an optical element that is displaceable in the optical axis direction, the stroke of the optical element can be reduced, but the effective diameter of the positive lens group is There is a possibility that it becomes too large or the effective diameter of the negative lens group becomes too small. Conversely, if the value of Δνd is increased, the axial chromatic aberration of the objective lens can be corrected satisfactorily even if the value of | fP / fN | is small, but the spherical aberration necessary for correcting the spherical aberration Since the amount of movement of the movable element of the means for correcting the fluctuation increases, the size of the optical system may increase. Therefore, the balance of these can be achieved by making the value of Δd · | fP / fN | / Δνd satisfy the above equation (5).

  The optical pickup device according to claims 16 and 17 is capable of recording and / or reproducing information with respect to at least two types of optical information recording media, and the means for correcting the fluctuation of the spherical aberration is transparent. For at least two types of optical information recording media having different substrate thicknesses, the divergence of the light beam incident on the objective lens is changed according to the thickness of each transparent substrate. And the fluctuation of spherical aberration that occurs when recording or reproduction is performed on each optical information recording medium is satisfactorily corrected, so that a good wavefront can always be formed on the information recording surface.

  The optical pickup device according to claims 18 and 19 is capable of recording and / or reproducing information with respect to an optical information recording medium in which a plurality of transparent substrates and information recording layers are laminated in order from the surface side of the optical information recording medium. Since the means for correcting the variation of the spherical aberration changes the divergence of the light beam incident on the objective lens according to the information recording layer when condensing each information recording layer, Since the difference in spherical aberration due to the difference in thickness to the information recording surface is corrected, and the variation in spherical aberration that occurs when recording or reproduction is performed on each information recording surface, it is possible to correct each information recording surface. In addition, a good wavefront can be formed on the 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. At this time, spherical aberration that varies depending on the thickness difference to the information recording surface is mainly the third order. Since it is a spherical aberration, the variation of the spherical aberration can be favorably corrected by shifting the movable element of the means for correcting the variation of the spherical aberration along the optical axis direction. Accordingly, it is possible to record or reproduce information twice or more on one side of the optical information recording medium.

  The optical pickup device according to claim 20 or 21, wherein 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 with respect to the information recording surface, the negative lens and the positive lens may be recorded more than when recording or reproducing information with respect to the information recording surface of the optical information recording medium having the transparent substrate thickness b. It is characterized by increasing the interval.

The optical pickup device according to claim 22 satisfies the following expression when the means for correcting the variation 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)
However,
fP: focal length of the positive lens group (however, when the positive lens group is provided with a diffractive surface, the total focal length combining the refractive power and the diffractive power)
fN: focal length of the negative lens group (however, when the negative lens group is provided with a diffractive surface, the total focal length combining the refractive power and the diffractive power)
The above equation (5) relates to the relationship of the paraxial power of the means for correcting the variation of the spherical aberration. When the objective lens is corrected to minimize the aberration under a combination of transparent substrates having a certain thickness, when the thickness of the transparent substrate changes, the means for correcting the variation of the spherical aberration 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 variation of the spherical aberration so as to satisfy the above formula (5), the stroke of the movable element can be made small, so that an overall compact optical system is obtained. be able to.

  25. The optical pickup device according to claim 24, wherein the means for correcting the variation of the spherical aberration includes a shift device that shifts the movable element along the optical axis in accordance with the variation of the spherical aberration. .

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

  An optical pickup device according to a twenty-sixth aspect is characterized in that 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 correction means from a plastic material, it is possible to reduce the burden on the shift device and to enable high-speed tracking. Furthermore, if the components providing the diffractive surface and the aspherical surface are formed from a plastic material, they can be easily added.

  The optical pickup device according to a twenty-seventh aspect is characterized in that the movable element is made of a plastic material. Thereby, since the weight reduction of an optical system can be achieved, the burden to the displacement apparatus of a movable element can be reduced. Moreover, it becomes easy to add a diffractive structure.

  The optical pickup device according to claim 28, wherein at least one of the positive lens and the negative lens has an aspheric surface on at least one surface thereof, and the optical pickup device according to claim 29, wherein the movable lens is movable. It is characterized by having an aspherical surface on at least one surface of the element. By having this aspherical surface, the means for correcting the fluctuation of the spherical aberration can obtain an optical system with good performance by the aberration correcting action of the aspherical surface. In particular, by providing the movable element with an aspheric surface, it is possible to prevent the wavefront aberration from being deteriorated at the time of decentering.

  The optical pickup device according to a thirty-third aspect is characterized in that the means for correcting the variation 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 variation 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. It is characterized by.

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

  In the optical pickup device according to claim 33, the means for correcting the variation of the spherical aberration includes an optical element having a diffractive surface having an annular diffractive structure. Since the correction can be performed effectively, it is not necessary to newly provide an optical element for correcting axial chromatic aberration, and the cost and space can be saved. The optical element having a diffractive surface includes one lens in the lens group, and therefore includes one of the positive lens group and the negative lens. In addition, the optical element is provided separately from those lenses.

  The optical pickup device according to a thirty-fourth aspect is characterized in that the means for correcting the variation of the spherical aberration includes an element capable of changing a refractive index distribution. Examples of such an element include, but are not limited to, an element SE using liquid crystal described later with reference to FIGS.

  36. An optical pickup device according to claim 35, comprising 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. And a photodetector for receiving reflected light from the optical information recording medium, wherein a variation in spherical aberration generated in the objective lens between the light source and the objective lens And a means for correcting the axial chromatic aberration generated in the objective lens, the spherical aberration of the objective lens that occurs when the oscillation wavelength of the semiconductor laser as the light source slightly fluctuates effectively, for example. Can be suppressed. Further, even when a change in refractive index occurs in the objective lens in accordance with changes in environmental temperature and humidity, it is possible to effectively suppress fluctuations in spherical aberration of the objective lens caused by the change. Furthermore, since axial chromatic aberration generated in the objective lens can be effectively corrected, even when instantaneous oscillation wavelength jump (mode hop) occurs that the spherical aberration correction means or the focusing of the objective lens cannot follow. A good wavefront can be formed on the recording surface.

  37. The optical pickup device according to claim 36, wherein the means for correcting the variation of the spherical aberration and the longitudinal chromatic aberration includes at least one positive lens and at least one negative lens, at least one of which is a light beam. It is a movable element that can be displaced in the axial direction. The optical pickup device according to claim 37, wherein the means for correcting the variation of the spherical aberration and the longitudinal chromatic aberration includes a positive lens group including a single positive lens and having a positive refractive power, and a single lens. And a negative lens group having negative refractive power, and at least one of the lens groups is a movable element that can be displaced in the optical axis direction.

  In the optical pickup device used for the short wavelength light source, as described above, the variation of the spherical aberration due to the wavelength variation of the light source and the temperature / humidity variation 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 light source with a short wavelength, it is necessary to provide means for correcting the variation of these spherical aberrations. When the spherical aberration of the objective lens fluctuates due to minute fluctuations in the oscillation wavelength of the light source or changes in temperature and humidity, a movable element of means for correcting the fluctuation of the spherical aberration and the longitudinal chromatic aberration is appropriately set. The variation of the spherical aberration can be corrected by changing the divergence of the light beam incident on the objective lens so as to minimize the spherical aberration of the wavefront formed on the information recording surface.

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

  The above equation (1) relates to correction of axial chromatic aberration. When spherical aberration of the objective lens fluctuates due to minute fluctuations in the oscillation wavelength of the light source, changes in temperature and humidity, etc., means for correcting this, for example, using an optical element capable of shifting 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 so that the spherical aberration of the objective lens is minimized. The axial chromatic aberration of the objective lens, which is a problem by using a short wavelength light source, can be corrected by configuring the means for correcting the variation 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 longitudinal chromatic aberration so as to satisfy the above formula (1), the chromatic aberration generated in the objective lens is opposite in polarity. Chromatic aberration can be generated. Accordingly, since the axial chromatic aberration cancels out, the wavefront when focused on the optical information recording medium through the objective lens and the means for correcting the variation of the spherical aberration and the axial chromatic aberration is: The axial chromatic aberration is kept small. If a diffractive surface is added to the objective lens and / or means for correcting the variation of the spherical aberration and the longitudinal chromatic aberration, and the diffractive lens is such that the back focus of the objective lens is shortened on the long wavelength side, the aberration is reduced. It becomes possible to correct more favorably. In this case, since the role of axial chromatic aberration correction can be shared by the means for correcting the spherical aberration variation and the axial chromatic aberration and the diffraction surface, the spherical aberration variation and the axial chromatic aberration are corrected. For example, when the means is configured using an optical element that can be shifted in the optical axis direction, the stroke of the optical element can be small.

  Furthermore, the power of the diffractive surface can be reduced by sharing the role of correcting the axial chromatic aberration between the spherical aberration variation and the means for correcting the axial chromatic aberration and the diffractive surface. This increases the spacing of the diffractive lens, which makes it easy to manufacture a diffractive lens having high diffraction efficiency. Therefore, the spherical aberration of the entire optical system, even when wavelength fluctuations, temperature / humidity changes, etc. occur without separately providing means for correcting the spherical aberration fluctuation and means for correcting axial chromatic aberration, In addition, a compact optical pickup device in which the longitudinal chromatic aberration is corrected favorably can be obtained.

  The optical pickup device according to claims 40 and 41 is characterized in that the νdP and the νdN satisfy the above expressions (2) and (3).

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

  The optical pickup device according to claim 42, wherein the means for correcting the variation of the spherical aberration and the longitudinal chromatic aberration is composed of a positive lens group including the positive lens and a negative lens group including the negative lens. 44. The optical pickup apparatus according to claim 43, wherein the means for correcting the variation of the spherical aberration and the longitudinal chromatic aberration is satisfied as in the above expression (4). It is characterized by that.

  The above equation (4) is the amount of correction 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, the variation of the spherical aberration and the axial chromatic aberration. It is related with the balance of the moving amount | distance of the movable element of the means to correct | amend. 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 satisfactorily, and the objective lens caused by the wavelength variation or temperature / humidity change of the light source When the means for correcting the spherical aberration fluctuation and the axial chromatic aberration that can correct the spherical aberration fluctuation is configured using an optical element that can be displaced in the optical axis direction, the stroke of the optical element is reduced. Although it can be suppressed, there is a possibility that the effective diameter of the positive lens group becomes too large, or the effective diameter of the negative lens group becomes too small. Conversely, if the value of Δνd is increased, even if the value of | fP / fN | is small, the axial chromatic aberration of the objective lens can be corrected satisfactorily. Since the amount of movement of the movable element of the means for correcting the aberration variation and the axial chromatic aberration increases, the size of the optical system may increase. Therefore, the balance of these can be achieved by making the value of Δd · | fP / fN | / Δνd satisfy the above equation (5).

45. The optical pickup device according to claim 44, wherein the means for correcting the variation of the spherical aberration and the axial chromatic aberration comprises a positive lens group including the positive lens and a negative lens group including the negative lens. The optical pickup apparatus according to claim 45 is characterized in that the means for correcting the variation of the spherical aberration and the longitudinal chromatic aberration satisfies the following expression.
Δd · | fP / fN | ≦ 0.50 (6)
However,
Δd: Amount of movement (mm) of the movable element when information is recorded or reproduced on one information recording surface of any one optical information recording medium capable of recording or reproducing information
fP: focal length (mm) of the positive lens group (however, when the positive lens group is provided with a diffractive surface, the total focal length combining the refractive power and the diffractive power)
fN: focal length (mm) of the negative lens group (however, when the positive lens group is provided with a diffractive surface, the total focal length combining the refractive power and the diffractive 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 (6) is the correction amount of the longitudinal chromatic aberration of the objective lens The present invention relates to the paraxial power of the means for correcting the variation of the spherical aberration and the axial chromatic aberration, and the balance of the moving amount of the movable element of the means for correcting the variation of the spherical aberration and the axial chromatic aberration. The refractive power as a refractive lens of the means for correcting the variation of the spherical aberration and the axial chromatic aberration, and the diffractive power of the diffraction surface added to the means for correcting the variation of the spherical aberration and the axial chromatic aberration are appropriately set. By combining them, axial chromatic aberration of the objective lens can be corrected. At this time, for example, means for correcting the variation of the spherical aberration and the longitudinal chromatic aberration for correcting the variation of the spherical aberration of the objective lens due to the variation of the oscillation wavelength of the light source or the change of temperature and humidity is provided in the optical axis direction. In the case of using a shiftable optical element, there is a problem that spherical aberration cannot be corrected satisfactorily if the stroke of the optical element is too large. Therefore, in the above equation (6), by setting the value of Δd · | fP / fN | to 0.50 or less, the balance between the correction of axial chromatic aberration and the correction of spherical aberration of the objective lens can be maintained well. I can do it.

  The optical pickup device according to claims 46 and 47 is capable of recording and / or reproducing information with respect to at least two types of optical information recording media, wherein the variation in spherical aberration and the longitudinal chromatic aberration are detected. The correcting means changes the divergence of the 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. Since the difference in spherical aberration due to the difference is corrected and the variation in spherical aberration that occurs when recording or reproduction is performed on each optical information recording medium is well corrected, a good wavefront is always formed on the information recording surface. Can do.

  The optical pickup device according to claims 48 and 49 is capable of recording and / or reproducing information on an optical information recording medium in which a plurality of transparent substrates and information recording layers are laminated in order from the surface side of the optical information recording medium. When the means for correcting the variation of the spherical aberration and the axial chromatic aberration are focused on the respective information recording layers, the light flux incident on the objective lens according to the information recording layer Since the divergence is changed, the difference in spherical aberration due to the difference in thickness up to the information recording surface is corrected, and the variation in spherical aberration that occurs when performing recording or reproduction on each information recording surface is favorably corrected. 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 optical axis direction, it is possible to focus on one desired information recording surface. At this time, spherical aberration that varies depending on the thickness difference to the information recording surface is mainly the third order. Since it is a spherical aberration, it is possible to satisfactorily correct the variation of the spherical aberration by shifting the movable element of the means for correcting the variation of the spherical aberration and the longitudinal chromatic aberration along the optical axis direction. Accordingly, it is possible to record or reproduce information twice or more on one side of the optical information recording medium.

  The optical pickup device according to claim 50 or 51, wherein 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 with respect to the information recording surface, the negative lens and the positive lens may be recorded more than when recording or reproducing information with respect to the information recording surface of the optical information recording medium having the transparent substrate thickness b. It is characterized by increasing the interval.

  The optical pickup device according to claim 52, wherein the means for correcting the variation of the spherical aberration and the longitudinal chromatic aberration is composed of a positive lens group including the positive lens and a negative lens group including the negative lens. The optical pickup device according to claim 53 satisfies the above expression (5).

  Equation (5) above relates to the relationship between the paraxial power of the means for correcting the variation of the spherical aberration and the axial chromatic aberration. When the objective lens is corrected to minimize aberration under 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 longitudinal chromatic aberration By moving the movable element in the means for correcting the above, 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 variation of the spherical aberration and the axial chromatic aberration so as to satisfy the above formula (5), the stroke of the movable element can be reduced. A compact optical system can be obtained.

  55. The optical pickup device according to claim 54, wherein the means for correcting the variation of the spherical aberration and the longitudinal chromatic aberration causes the movable element to move along the optical axis in accordance with the variation of the spherical aberration. It is characterized by having.

  An optical pickup device according to a 55th aspect is characterized in that the movable element is made of a material having a specific gravity of 2.0 or less. Thereby, the burden to the displacement apparatus of a movable element can be reduced.

  The optical pickup device according to claim 56, wherein at least one of the positive lens and the negative lens is made of a plastic material. In particular, by forming the movable element of the means for correcting the variation of the spherical aberration and the axial chromatic aberration from a plastic material, it is possible to reduce the burden on the shift device and to perform high-speed tracking. Furthermore, if the components 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 57th aspect is characterized in that the movable element is made of a plastic material. Thereby, since the weight reduction of an optical system can be achieved, the burden to the displacement apparatus of a movable element can be reduced. Moreover, it becomes easy to add a diffractive structure.

  59. 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 thereof, and the optical pickup device according to claim 59, wherein the movable lens is movable. It is characterized by having an aspherical surface on at least one surface of the element. 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 with good performance by the aberration correcting action of the aspherical surface. In particular, by providing the movable element with an aspheric surface, it is possible to prevent the wavefront aberration from being deteriorated at the time of decentering.

  The optical pickup device according to claim 60, wherein the means for correcting the variation of the spherical aberration and the longitudinal chromatic aberration is made of a material having a saturated water absorption of 0.5% or less. .

  The optical pickup device according to claim 61, wherein the means for correcting the variation of the spherical aberration and the longitudinal chromatic aberration has 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. It is formed from the material which is.

  The optical pickup device according to claim 62, wherein the means for correcting the variation of the spherical aberration and the longitudinal chromatic aberration comprises the one positive lens and the one negative lens. To do.

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

  The optical pickup device according to a 64th aspect is characterized in that the means for correcting the fluctuation of the spherical aberration and the longitudinal chromatic aberration includes an element capable of changing a refractive index distribution.

  The optical pickup device according to claim 65, wherein the means for correcting the variation 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. And

  An optical pickup device according to a 66th aspect has an optical element having a diffraction surface having a ring-shaped diffraction structure.

  The optical pickup device according to a 67th aspect is characterized in that the objective lens is the optical element (an optical element having a diffractive surface having an annular diffractive structure).

An optical pickup device according to a 68th aspect is characterized in that 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 (7)
However,
fD: The diffractive structure of the objective lens is represented by an optical path difference function defined by Φb = b ₂ h ² + b ₄ h ⁴ + b ₆ h ⁶ +... (where h is a height from the optical axis) a _(mm), b _2, b 4, _{b 6,} ......... secondary, fourth, sixth, an optical path difference function coefficients of .........) time, fD = 1 / (- 2 · b ₂ ) The focal length at the oscillation wavelength of the light source defined by only the diffractive structure of the objective lens. F: The objective lens combining the refractive power of the objective lens and the diffractive power of the diffractive structure of the objective lens. 69. The focal length at the oscillation wavelength of the entire light source The optical pickup device according to claim 68, wherein the objective lens is used in an optical pickup device capable of satisfactorily correcting a variation in spherical aberration occurring on each optical surface of a condensing optical system. Correction of longitudinal chromatic aberration About. When using a short wavelength laser light source having an oscillation wavelength of about 400 nm and an objective lens having a high image side numerical aperture of about NA 0.85, correction of axial chromatic aberration generated in the objective lens can be an important problem for the reasons described above. This problem is solved by providing the objective lens with a diffractive structure having a focal length that satisfies the above formula (7). This diffractive structure has such a wavelength characteristic that when the oscillation wavelength of the laser light source fluctuates to the longer wavelength side, the back focus changes in the direction of shortening. The axial chromatic aberration generated in the objective lens can be corrected by appropriately selecting the power so as to satisfy the above formula (7). It is possible to prevent the axial chromatic aberration of the objective lens from being overcorrected when the value of fD / f is equal to or higher than the lower limit of the above formula (7), and to prevent the axial chromatic aberration of the objective lens from being excessively corrected when the value is lower than the upper limit. . Further, if the axial chromatic aberration of the objective lens is excessively corrected, it is preferable that the axial chromatic aberration generated in each optical element included in the condensing optical system can be canceled by the objective lens.

  70. The optical pickup device according to claim 69, wherein the diffractive structure is an n-order diffracted light having a diffracted light quantity larger than that of any of the other orders of diffracted light generated by the diffractive structure (herein , N is an integer other than −1, 0, and +1), and the optical information recording medium is used for recording and / or reproducing information with respect to the optical information recording medium. It is possible to focus on the information recording surface of the recording medium.

  The optical pickup device according to claim 69 is used for an optical pickup device that records or reproduces information on an optical information recording medium by using second-order or higher-order diffracted light generated by a diffractive structure. The present invention relates to an optical system. When the n-th order diffracted light is used, compared to the case where the + 1st order or −1st order diffracted light is used, the ring interval (ring zone pitch) of the diffractive structure is about n times and the number of ring zones is about 1 Since it can be multiplied by n, it is easy to manufacture a lens mold for adding a diffractive structure, the processing time of the mold can be shortened, and the diffraction efficiency is reduced due to processing and manufacturing errors. Can be prevented.

  The optical pickup device according to claim 70, wherein the optical pickup device includes an optical element having a diffractive surface having an annular diffraction structure, and the means for correcting the variation of the spherical aberration includes each of the positive lenses including the positive lens. 72. The optical pickup device according to claim 71, wherein the Abbe number is 70.0 or less, or each Abbe number of all negative lenses including the negative lens is 40.0 or more. The optical element having a diffractive surface having a diffractive structure, and the means for correcting the variation of the spherical aberration and the longitudinal chromatic aberration, each Abbe number of the positive lens including the positive lens is 70.0 or less Alternatively, the Abbe number of each of all negative lenses including the negative lens is 40.0 or more.

  The optical pickup device according to claim 70 relates to a preferable configuration of the means for correcting the variation of the spherical aberration capable of correcting the axial chromatic aberration generated in the objective lens, and the optical pickup device according to claim 71, The present invention relates to a preferable configuration of means for correcting the variation of the spherical aberration and the axial chromatic aberration that can correct 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 or less, or the Abbe number of the negative lens is 40.0 or more. In some cases, the longitudinal chromatic aberration that occurs in the objective lens tends to be under-corrected. At this time, a diffractive surface having a diffractive structure having a wavelength characteristic that shortens the back focus of the objective lens when the oscillation wavelength of the light source slightly fluctuates toward the long wavelength side, By providing at least one surface of a component 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 well. Furthermore, this diffractive surface has a spherical aberration characteristic that causes the spherical aberration of the objective lens to be undercorrected when the oscillation wavelength of the light source slightly fluctuates to the long wavelength side, so that the oscillation wavelength of the light source is on the long wavelength side. It is also possible to correct spherical aberration when a slight fluctuation occurs. Further, 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 also 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. Both the positive lens and the negative lens preferably have an Abbe number of 40.0 or more and 70.0 or less.

An optical pickup device according to a 72nd aspect has means for correcting the variation of the spherical aberration, and an optical pickup device according to the 73rd aspect has means for correcting the variation in the spherical aberration and the axial chromatic aberration, respectively. When the paraxial power at the oscillation wavelength of the light source is P1, the paraxial power at a wavelength 10 nm shorter than the oscillation wavelength is P2, and the paraxial power at a wavelength 10 nm longer than the oscillation wavelength is P3, the following equation is satisfied. It is characterized by doing.
P2 <P1 <P3 (8)
As a result, 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 serves to correct the axial chromatic aberration generated in an optical element such as an objective lens or a coupling lens. Can be given. That is, the means for correcting the variation of the spherical aberration by the diffractive structure itself or the means for correcting the variation of the spherical aberration and the axial chromatic aberration excessively corrects the axial chromatic aberration, and the objective lens, the coupling lens, etc. By generating axial chromatic aberration having a polarity opposite to that of the axial chromatic aberration generated in the optical element, it is possible to correct the axial chromatic aberration generated in the optical element such as an objective lens or a coupling lens.

  An optical pickup device according to a 74th aspect is characterized in that the diffractive surface has a function of suppressing axial chromatic aberration generated in the objective lens with respect to minute fluctuations in the oscillation wavelength of the light source.

  75. The optical pickup device according to claim 75, wherein 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 the long wavelength side. And Thereby, the axial chromatic aberration of the objective lens can be favorably corrected. In particular, by correcting axial chromatic aberration generated in the objective lens by providing a diffractive surface on the coupling lens and / or objective lens, the moment when spherical aberration variation means and focusing of the objective lens cannot follow, such as mode hopping Even when a wavelength change occurs, the spot diameter does not increase, and stable information recording or reproduction is possible.

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

  The optical pickup device according to claim 77, wherein the light source includes at least two light sources, a light source having an oscillation wavelength λ1 and a light source having an oscillation wavelength λ2 (λ1 <λ2), and the condensing optical system includes the oscillation optical system. A predetermined numerical aperture on the image side of the objective lens necessary for recording or reproducing information with respect to the information recording surface of the first optical information recording medium having the transparent substrate thickness t1 is emitted from the light source having the wavelength λ1. The second light flux emitted from the light source having the oscillation wavelength λ2 can be condensed with a wavefront aberration of 0.07λ1 rms or less in the second optical information recording medium having a transparent substrate thickness t2 (t1 ≦ t2). The light beam can be condensed with a wavefront aberration of 0.07λ2 rms or less within a predetermined numerical aperture on the image side of the objective lens necessary for recording or reproducing information on the recording surface.

  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, an objective lens is applied to one optical information recording medium. If the spherical aberration correction is designed to be optimal, large spherical aberration will occur 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 of t2 (> t1) When recording or reproducing an optical information recording medium having a thickness, an overcorrected spherical aberration occurs in the objective lens. Conversely, when an optical information recording medium having a transparent substrate thickness of t2 '(<t1) is to be recorded or reproduced, spherical aberration that is insufficiently corrected occurs in the objective lens.

  On the other hand, for example, a diffractive surface is added to the objective lens, and the diffractive lens has a wavelength dependency such that light beams of different wavelengths form good wavefronts for optical information recording media having different transparent substrate thicknesses. Thus, it is possible to satisfactorily correct spherical aberration when the transparent substrate thickness is different. 78. The optical pickup device according to claim 77, wherein short-wavelength diffracted light forms a good wavefront with respect to an optical information recording medium having a small transparent substrate thickness, and long-wavelength diffracted light has a large transparent substrate thickness. A good wavefront is preferably formed 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 is insufficiently corrected when the wavelength of the light source slightly fluctuates toward the long wavelength side. Further, a divergence angle changing means for changing the divergence angle of the light beam is provided, and the divergence degree of the light beam incident on the objective lens is changed to a divergence degree corresponding to the object distance at which the spherical aberration is minimized. The spherical aberration of the lens can be corrected better. In particular, if the luminous flux at the time of minimum spherical aberration with respect to the optical information recording medium having the transparent substrate thickness of t2 is divergent light, it is easy to ensure the working distance. Since the role of correcting spherical aberration deterioration when the transparent substrate thickness is different can be shared by the divergence changing means and the diffraction surface, the amount of movement of the movable part of the divergence changing means can be small. Also, the power of the diffractive surface can be reduced by sharing the role of spherical aberration correction by the divergence changing means and the diffractive surface, and the diffractive lens with high diffraction efficiency can be obtained by increasing the distance between the diffracting ring zones. Easy to manufacture. In the above description, the objective lens is corrected so that the spherical aberration is minimized with respect to the infinity light beam in combination with the transparent substrate thickness t1, but the divergent light beam or the image from a finite distance is used. Needless to say, the spherical aberration can be corrected when the thickness of the transparent substrate is different by the same method as described above.

  An optical pickup device according to a 78th aspect is characterized by including an optical element having a diffractive surface having an annular diffractive structure.

  79. The optical pickup device according to claim 79, wherein the diffractive surface of the optical element transmits the first light flux emitted from the light source having the oscillation wavelength λ1 to the first optical information recording medium having a transparent substrate thickness t1. The light can be condensed with a wavefront aberration of 0.07λ1 rms or less within a predetermined numerical aperture on the image side of the objective lens necessary for recording or reproducing information on the information recording surface, and the oscillation wavelength λ2 (λ1 <λ2). The image of the objective lens necessary for recording or reproducing information on the information recording surface of the second optical information recording medium having the transparent substrate thickness t2 (t1 ≦ t2) is emitted from the second light flux emitted from the light source. The wavelength characteristic is such that the light can be condensed within a wavefront aberration of 0.07λ2 rms or less within a predetermined numerical aperture on the side. Specifically, the spherical aberration caused by the difference in the thickness of the transparent substrate, the difference in the oscillation wavelength of two light sources used for recording and / or reproducing information on each optical information recording medium, and the diffraction surface Correction is performed using the action of the diffractive structure provided in FIG.

  The optical pickup device according to claim 80 is required for recording or reproducing information by the first light beam emitted from the light source having the oscillation wavelength λ1 with respect to the information recording surface of the first optical information recording medium. The predetermined numerical aperture on the image side of the objective lens is NA1, and information is recorded by the second light flux emitted from the light source having the oscillation wavelength λ2 on the information recording surface of the second information recording medium. When the predetermined numerical aperture on the image side of the objective lens necessary for reproduction is NA2 (NA1> NA2), the diffractive surface of the optical element reflects the second light flux emitted from the light source having the oscillation wavelength λ2. The optical information recording surface of the second optical information recording medium is condensed with a wavefront aberration of 0.07λ2 rms or more in the NA1.

  In particular, as described in claim 80, the spherical aberration is satisfactorily corrected for the combination of the oscillation wavelength λ1, the transparent substrate thickness t1, and the image-side numerical aperture NA1, and the oscillation wavelength λ2 and the transparent substrate thickness The spherical aberration up to the range of the image side numerical aperture NA2 required for the combination of the length t2 and the image side numerical aperture NA2 is corrected by the action of the diffraction structure, and the range from the image side numerical aperture NA2 to NA1 is spherical aberration. It is preferable to increase the value (to generate a large amount as a flare component). As a result, when the second light flux having the oscillation wavelength λ2 is incident so as to pass through all of the diaphragm determined by the oscillation wavelength λ1 and the image-side numerical aperture NA1 of the objective lens, the light flux having the image-side numerical aperture NA2 or more is Since the spot diameter does not become too small on the information recording surface with respect to the first optical information recording medium having the transparent substrate thickness t1 without contributing to spot image formation, an error signal is generated in the light receiving means of the optical pickup device. In addition, it is possible to prevent detection of unnecessary signals, and it is not necessary to provide means for switching the aperture according to the combination of the oscillation wavelength of each light source and the corresponding image-side numerical aperture, so that a simple optical pickup A device can be obtained. In particular, the second light flux emitted from the light source having the oscillation wavelength λ2 is condensed with a wavefront aberration of 0.2λ2 rms or more in the NA1 with respect to the information recording surface of the second optical information recording medium. It is more preferable.

  The optical pickup device according to claim 81 is characterized in that the objective lens is the optical element (an optical element having a diffractive surface having a ring-shaped diffraction structure).

The optical pickup device according to claim 82 is characterized in that the objective lens is a single objective lens having at least one aspheric surface and satisfies the following expression.
0.5 ≦ (f1 / νd) · fD1 ≦ 10.0 (9)
However,
f1: Focal length (mm) of the entire objective lens at the oscillation wavelength λ1, which is obtained by combining the refractive power of the objective lens and the diffraction power of the objective lens by the diffraction structure
νd: d-line Abbe number of the objective lens fD1: the diffraction structure of the objective lens is represented by an optical path difference function defined by Φb = b ₂ h ² + b ₄ h ⁴ + b ₆ h ⁶ +. Here, h is a height (mm) from the optical axis, and b ₂ , b ₄ , b ₆ ,... Are second-order, fourth-order, sixth-order,. Where fD = 1 / (− 2 · b ₂ ), focal length (mm) at the oscillation wavelength λ1 due to only the diffractive structure of the objective lens
An optical pickup device according to an 83rd aspect is characterized in that 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 (10)
However,
b ₂ : The diffractive structure of the objective lens is represented by an optical path difference function defined by Φb = b ₂ h ² + b ₄ h ⁴ + b ₆ h ⁶ +... (where h is a height from the optical axis) is a _(mm), b _2, b 4, _{b 6,} ......... secondary, fourth, sixth, an optical path difference function coefficients of .........) Part 2 order optical path difference function coefficient when λ1: the oscillation wavelength λ1 (mm)
84. The optical pickup device according to claim 82, wherein the optical chromatic aberration generated by the objective lens and the spherical surface generated by each optical surface of the condensing optical system for a plurality of optical information recording media having different transparent substrate thicknesses. The present invention relates to an optical pickup device that can satisfactorily correct aberration fluctuations. In particular, in an optical pickup device that uses diffracted light of the same order with respect to light beams of a plurality of light sources having different wavelengths, a diffractive structure is provided in an objective lens and the diffraction is performed. The present invention relates to a case where axial chromatic aberration of the diffracted light of the same order is corrected by the action of the structure.

  When using a short wavelength light source (oscillation wavelength of about 500 nm or less) and an objective lens having an image side numerical aperture higher than a conventional image side numerical aperture (for example, about NA 0.45 for CD and about NA 0.6 for DVD) In order to suppress the occurrence of coma aberration, it is particularly effective to make the transparent substrate thickness of the optical information recording medium as small as 0.2 mm or less. On-axis chromatic aberration is not overcorrected or undercorrected for both luminous fluxes of a long wavelength light source, and can be corrected in a well-balanced manner. On the other hand, by providing the objective lens with a diffractive structure having a wavelength characteristic that forms a good spot on each information recording surface, a conventional transparent substrate thickness (for example, 1 for a CD). Recording or reproducing information with a single optical pickup device (at least an optical pickup device sharing the objective lens and its driving mechanism) even on an optical information recording medium having a large size (2 mm, 0.6 mm for DVD) Is possible. In the above equation (9), the axial chromatic aberration is not excessively corrected with respect to the light beam of the long wavelength light source of 600 nm to 800 nm above the lower limit of the left side, and the light beam of the short wavelength light source of 500 nm or less is 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.

Further, by satisfying the above formula (10), it is possible to reduce the burden of aberration correction in the diffractive structure provided in the objective lens, that is, by satisfying the above formula (10), the diffractive structure provided in the objective lens Since it can be made to have little role in correcting the longitudinal chromatic aberration generated in the condensing optical system, an objective lens having a high diffraction efficiency can be obtained with a large ring interval of the diffractive structure, a small number of ring zones. . Here, b ₂ = 0 corresponds to the case where the axial chromatic aberration generated in the condensing optical system is not corrected by the diffractive structure provided in the objective lens, and −25.0 ≦ (b ₂ / λ1) < In the case of 0.0, the axial chromatic aberration for the light beam of the short wavelength light source (about 500 nm or less) is such that the axial chromatic aberration is not overcorrected for the light beam of the long wavelength light source (about 600 nm to 800 nm). This corresponds to the case where correction is made. 66. The structure according to claim 10, 11, 33, 38, 39, 63, or 65, wherein the axial chromatic aberration undercorrected in this way corrects the variation of the spherical aberration arranged between the objective lens and the light source. This can be corrected. Further, when the axial chromatic aberration generated in the objective lens is corrected by the action of the diffractive structure, it is preferable that νd> 55.0 is satisfied when the Abbe number of the material of the objective lens is νd, whereby the secondary spectrum. Can be kept small.

  The optical pickup device according to claim 84, wherein 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.

  In the optical pickup device according to claim 85, since 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 toward the long wavelength side. It is possible to satisfactorily correct the axial chromatic aberration that is a problem when using a wavelength light source.

  The optical pickup device according to claim 86, wherein the diffractive surface is a spherical surface that changes in a direction such that the spherical aberration of the objective lens is insufficiently corrected when the oscillation wavelength of the light source slightly fluctuates toward the long wavelength side. It has an aberration characteristic. As a result, 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 diffraction surface. When the means for correcting the aberration or the means for correcting the variation of the spherical aberration and the axial chromatic aberration is configured using an optical element that can be shifted 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 diffractive surface with 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, and the diffraction surface. Since the power of the diffractive surface can be suppressed and the distance between the diffraction zones can be increased, an optical element with high diffraction efficiency can be easily manufactured.

  90. The optical pickup device according to claim 87, wherein the objective lens divides a light beam emitted from the light source by a refraction action into a plurality of light beams on at least one surface in order from the optical axis side toward the outer periphery thereof. And having at least a first portion, a second portion, and a third portion, wherein the first portion and the third portion are information recording surfaces of the first optical information recording medium having a transparent substrate thickness t1. The light beam from the light source can be condensed so that information can be recorded or reproduced, and the first part and the second part have a transparent substrate thickness t2 (t1 <t2). The light beam from the light source can be condensed so that information can be recorded on or reproduced from the information recording surface of the second optical information recording medium.

The optical pickup device according to claim 89, wherein at least one surface of the objective lens is provided with k incident light beams (k ≧ 4) in a ring-shaped light beam (wherein, from the optical axis side to the outside thereof) by refraction. Forming a ring-shaped step portion that is divided into first, second,...
When recording and / or reproducing information on 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 formed by the first and k-th light beams is 0.05λ1 rms or less (λ1 light source wavelength), and the second to (k− 1) Among the light beams, at least two of the light beams have an apparent best image plane position formed at a position different from the best image plane position formed by the first and kth light beams, and the first and kth light beams. The wavefront aberration of each of the first to k-th light beams passing through the required numerical aperture with respect to the first optical information recording medium at the best image plane position formed by the light beam is approximately miλ1 (where mi is an integer). I = 1, 2,..., K).

  According to the optical pickup device of claim 89, the transparent substrate thickness of the first optical information recording medium (first optical disc) and the second optical disc are divided by a plurality of dividing surfaces divided by the annular zone step. Residual error is reduced in the substrate thickness difference from the transparent substrate thickness of the optical information recording medium (second optical disc), so that information can be recorded and / or reproduced appropriately for multiple types of optical discs. Can be done. Such an objective lens will be described later with reference to FIG.

  The optical pickup device according to claim 90, wherein the transparent substrate thickness t1 of the first optical information recording medium is 0.6 mm or less, and the transparent substrate thickness t2 of the second optical information recording medium is 0. It is 6 mm or more, and the oscillation wavelength λ2 is in the range of 600 nm to 800 nm.

The optical pickup device according to claim 91, wherein the third-order spherical aberration component of the spherical aberration of the objective lens is SA1, and the sum of the fifth-order, seventh-order, and ninth-order spherical aberration components is SA2. It is characterized by satisfying the formula.
| SA1 / SA2 |> 1.0 (11)
However,
SA1: Third-order spherical aberration component when the aberration function is expanded into a Zernike polynomial SA2: Fifth-order spherical aberration component and seventh-order spherical aberration when the aberration function is expanded into a Zernike polynomial The optical pickup apparatus according to claim 91 relates to a balance in a spherical aberration component of a substantial order of spherical aberration generated in an objective lens. In particular, in a single 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). In addition, when a lens is manufactured by molding, it is difficult to obtain a plurality of lenses with a center thickness of a few μm or less. Since the spherical aberration component can be corrected relatively easily by 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, the tolerance of the center thickness (in particular, (Error from design value) can be expanded.

  The optical pickup device according to claim 92, wherein a diaphragm for determining a numerical aperture of the objective lens is positioned on a side where the optical information recording medium is disposed with respect to a surface vertex of the surface closest to the light source of the objective lens. It is characterized by. Thus, when divergent light is incident on the objective lens, the light beam passing height on the surface closest to the light source of the objective lens can be kept small, which is preferable in terms of downsizing the objective lens or correcting aberrations.

  In the optical pickup device according to claim 93, since the objective lens is a single objective lens having an aspheric surface on at least one surface, it is possible to effectively correct spherical aberration or coma aberration, and it is small and light and compact. An 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 according to 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, the longitudinal chromatic aberration, which is a problem when using a short wavelength light source with an oscillation wavelength of 500 nm or less, is particularly corrected by adopting the configuration according to claim 10, 11, 33, 38, 39, 63 or 65. be able to.

  The optical pickup device according to claim 95 is characterized in that an image-side numerical aperture NA of the objective lens is at least 0.65 or more. By increasing the image side numerical aperture of the objective lens to 0.65 or more (more preferably 0.75 or more) as compared with the conventional lens, it is possible to achieve higher density and larger capacity of the optical information recording medium. Hereinafter, specific numerical values will be described. The spot diameter focused 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), so a blue-violet semiconductor with an oscillation wavelength of 400 nm 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 The spot diameter is about ½. Here, since the recording density on the optical information recording medium is proportional to the square of the inverse 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 apparatus according to claim 96 is characterized in that the objective lens satisfies the following expression.
1.1 ≦ d1 / f ≦ 3.0 (12)
However,
d1: On-axis lens thickness (mm)
f: Focal length (mm) at the oscillation wavelength of the light source (however, if the light source has a plurality of light sources having different oscillation wavelengths, the focal length at the oscillation wavelength with the shortest wavelength, and a diffraction surface on the objective lens) If equipped, the total focal length combining the refractive power and diffraction 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 equal to or greater than the lower limit, good image height characteristics can be ensured and shift sensitivity can be reduced. In addition, since the angle formed 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, it is easy to process the mold during lens molding. become. On the other hand, if the value d1 / f is equal to or greater than the upper limit, the center thickness (axial thickness) does not become too large, so that a large working distance can be ensured. In addition, since the occurrence of astigmatism can be suppressed to a low level, good image height characteristics can be ensured. From the above, it is more desirable that the value d1 / f satisfies the following formula.
1.2 ≦ d1 / f ≦ 2.3 (12 ′)
Moreover, it is particularly desirable to satisfy the following formula.
1.4 ≦ d1 / f ≦ 1.8 (12 ″)
The optical pickup apparatus according to claim 97 is characterized in that the objective lens is made 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. Furthermore, when an aspherical surface and a diffractive surface are provided on the objective lens, they can be easily formed. In particular, it is preferable to manufacture by injection molding (including injection compression molding).

  An optical pickup device according to a 98th aspect is characterized in that the objective lens is made of a material having a saturated water absorption rate of 0.5% or less. This is preferable because the refractive index change of the objective lens due to moisture absorption is reduced.

  The optical pickup device according to claim 99, wherein 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 light having an oscillation wavelength of the light source. To do. Thereby, since a light source having high light intensity is not required, energy saving can be achieved.

  The objective lens according to a 100th aspect is applicable to the optical pickup device according to any one of the 1st to 99th aspects.

  An objective lens according to a 101st aspect is the objective lens used in the optical pickup device according to any of the 1st to 99th aspects.

The objective lens according to claim 102 is an optical pickup device capable of recording and / or reproducing information with respect to at least two types of optical information recording media, the light source having an oscillation wavelength λ1, and the oscillation wavelength λ1. The information recording of the first optical information recording medium through the transparent substrate having the transparent substrate thickness t1 is performed by using a light source having a different oscillation wavelength λ2 (λ1 <λ2) and a first light beam emitted from the light source having the oscillation wavelength λ1. The second light beam emitted from the light source having the oscillation wavelength λ2 is condensed on the surface and the information recording surface of the second optical information recording medium is passed through the transparent substrate having the transparent substrate thickness t2 (t1 ≦ t2). In an objective lens for an optical pickup device, comprising: a condensing optical system including an objective lens that condenses the light; and a photodetector that receives reflected light from the first and second optical information recording media. Characterized by satisfying the formula The objective lens.
1.1 ≦ d1 / f ≦ 3.0 (13)
However,
d1: On-axis lens thickness (mm)
f: Focal length (mm) at the oscillation wavelength λ1 (however, when the objective lens is provided with a diffractive surface, the total focal length combining the refractive power and the diffractive power)
The objective lens described in Item 103 is characterized in that the image-side numerical aperture NA is 0.75 or more.

  An objective lens according to a 104th aspect is characterized by including a diffractive surface having an annular diffractive structure.

  The objective lens according to claim 105, wherein the diffractive surface transmits 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. The second light flux emitted from the light source having the oscillation wavelength λ2 can be condensed with a wavefront aberration of 0.07λ1 rms or less within a predetermined numerical aperture on the image side of the objective lens necessary for recording or reproduction. 2. A wavelength characteristic capable of focusing on the information recording surface of the information recording medium 2 with a wavefront aberration of 0.07λ2 rms or less within a predetermined numerical aperture on the image side of the objective lens necessary for recording or reproducing information. It is characterized by having.

  The objective lens described in claim 106 is necessary for recording or reproducing information by the first light flux emitted from the light source having the oscillation wavelength λ1 with respect to the information recording surface of the first optical information recording medium. The predetermined numerical aperture on the image side of the objective lens is NA1, and information is recorded or reproduced by the second light flux emitted from the light source having the oscillation wavelength λ2 on the information recording surface of the second information recording medium. When the predetermined numerical aperture on the image side of the objective lens necessary for the above is NA2 (NA1> NA2), the diffractive surface transmits the second light flux emitted from the light source having the oscillation wavelength λ2 to the second The optical information recording medium is focused on the information recording surface within the NA1 with a wavefront aberration of 0.07λ2 rms or more.

  The objective lens described in claim 107 is characterized in that the diffractive 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 diffractive surface has a wavelength characteristic that shortens a back focus of the objective lens when an oscillation wavelength of the light source slightly fluctuates toward a long wavelength side. .

  The objective lens according to claim 109, wherein the diffractive surface has a spherical aberration characteristic that changes in a direction such that the spherical aberration of the objective lens is insufficiently corrected when the oscillation wavelength of the light source slightly fluctuates toward the long wavelength side. It is characterized by having.

The objective lens described in claim 110 is a single lens having at least one aspherical surface and satisfies the following expression.
0.5 ≦ (f1 / νd) · fD1 ≦ 10.0 (14)
However,
f1: Focal length (mm) at the oscillation wavelength λ1 obtained by combining the refractive power and the diffraction power by the diffraction structure
νd: d-line Abbe number of the lens material fD1: the diffraction structure is represented by an optical path difference function defined by Φb = b ₂ h ² + b ₄ h ⁴ + b ₆ h ⁶ +... (where h is FD = 1 when the height from the optical axis (mm) and b ₂ , b ₄ , b ₆ ,... Are second-order, fourth-order, sixth-order,. / (− 2 · b ₂ ), focal length (mm) at the oscillation wavelength λ1 due to the diffraction structure alone
By satisfying the above equation (14), the axial chromatic aberration is not overcorrected or undercorrected for both light beams of the short wavelength light source and the conventional long wavelength light source, and the correction is performed in a balanced manner. Can do. In the above equation (14), the axial chromatic aberration is not excessively corrected with respect to the light beam of the long wavelength light source of 600 nm to 800 nm above the lower limit of the left side, and the light beam of the short wavelength light source of 500 nm or less is 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. In addition, for a plurality of optical information recording media having different transparent substrate thicknesses, a conventional transparent substrate thickness (for example, The optical information recording medium with a thin transparent substrate that requires a short wavelength light source and a high image-side numerical aperture (for example, transparent) It is possible to obtain an objective lens that can also be used for recording or reproducing information for a substrate thickness of 0.2 mm or less.

The objective lens described in Item 111 is a single lens having at least one aspheric surface and satisfies the following expression.
-25.0 ≦ (b ₂ /λ1)≦0.0 (15)
However,
b ₂ : The diffraction structure is represented by an optical path difference function defined by Φb = b ₂ h ² + b ₄ h ⁴ + b ₆ h ⁶ +... (where h is a height (mm) from the optical axis) Where b ₂ , b ₄ , b ₆ ,... Are second-order, fourth-order, sixth-order,...)) Second-order optical path difference function coefficients. Wavelength λ1 (mm)
Further, by satisfying the above formula (15), it is possible to reduce the burden of aberration correction in the diffractive structure provided in the objective lens, that is, by satisfying the above formula (15), the diffractive structure provided in the objective lens Since it can be made to have little role in correcting the longitudinal chromatic aberration generated in the condensing optical system, an objective lens having a high diffraction efficiency can be obtained with a large ring interval of the diffractive structure, a small number of ring zones. . Here, b ₂ = 0 corresponds to the case where the axial chromatic aberration generated in the condensing optical system is not corrected by the diffractive structure provided in the objective lens, and −25.0 ≦ (b ₂ / λ1) < In the case of 0.0, the axial chromatic aberration for the light beam of the short wavelength light source (about 500 nm or less) is such that the axial chromatic aberration is not overcorrected for the light beam of the long wavelength light source (about 600 nm to 800 nm). This corresponds to the case where correction is made. 66. The structure according to claim 10, 11, 33, 38, 39, 63, or 65, wherein the axial chromatic aberration undercorrected in this way corrects the variation of the spherical aberration arranged between the objective lens and the light source. This can be corrected. Further, when the axial chromatic aberration generated in the objective lens is corrected by the action of the diffractive structure, it is preferable that νd> 55.0 is satisfied when the Abbe number of the material of the objective lens is νd, whereby the secondary spectrum. Can be kept small.

The objective lens according to claim 112 satisfies the following expression when the sum of the third-order spherical aberration components of SA1, the fifth-order, seventh-order, and ninth-order spherical aberration components is SA2. Features.
| SA1 / SA2 |> 1.0 (16)
However,
SA1: Third-order spherical aberration component when the aberration function is expanded into a Zernike polynomial SA2: Fifth-order spherical aberration component and seventh-order spherical aberration when the aberration function is expanded into a Zernike polynomial The square root of the sum of squares of the component and the ninth-order spherical aberration component relates to the balance of the spherical aberration component of the substantial order of the spherical aberration generated in the objective lens. In particular, in a single 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). In addition, when manufacturing lenses by molding, it is difficult to obtain a plurality of lenses with a center thickness of several μm or less, but by satisfying the above equation (11), The balance of the spherical aberration component of the substantial order of the generated spherical aberration can be improved, and the allowable range of center thickness required for the objective lens (particularly, an error from the design value) can be expanded.

  The objective lens according to claim 113, at least a first portion that divides a light beam emitted from the light source by a refracting action into a plurality of light beams on at least one surface in order from the optical axis side toward the outer periphery thereof. A second portion and a third portion, wherein the first portion and the third portion record or reproduce information on 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 condensed so that the first part and the second part can record information on the information recording surface of the second optical information recording medium. Alternatively, the light beam from the light source having the oscillation wavelength λ2 can be condensed so that reproduction can be performed.

  The objective lens according to claim 114, wherein at least one surface is provided with k incident light fluxes (k ≧ 4) due to refracting action (here, the first light beam is sequentially directed from the optical axis side toward the outside thereof). , Second,..., K-th luminous flux), and when recording and / or reproducing information with respect to the first optical information recording medium. The spherical aberration component of the wavefront aberration of the first and k-th beams at the best image plane position created by the first and k-th beams is 0.05λ1 rms or less (λ1 light source wavelength), and the second to ( k-1) At least two of the 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 kth light beams. The first optical information at the best image plane position generated by the k luminous flux. The wavefront aberration of the light beam in each of the first to kth light beams passing through the required numerical aperture for the recording medium is approximately miλ1 (mi is an integer, i = 1, 2,..., K ).

  The objective lens according to claim 115 is made of a plastic material.

  The objective lens described in Item 116 is formed of a material having a saturated water absorption rate of 0.5% or less.

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

  The objective lens according to claim 118 is a single lens having at least one aspheric surface.

  The objective lens described in Item 119 is applicable to the optical pickup device described in any one of Items 1 to 99.

  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 be displaced along the optical axis direction, and the positive lens A diffraction having an Abbe number of 70.0 or less or a total Abbe number of all negative lenses including the negative lens of 40.0 or more and having an annular diffraction structure on at least one surface It has a surface.

  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 (particularly preferably, an objective lens when applied to an optical pickup device) The axial chromatic aberration that occurs in (1) tends to be undercorrected, but by providing a diffractive surface, it is possible to correct the axial chromatic aberration satisfactorily. In particular, by providing at least one diffractive surface with a diffractive structure having a wavelength characteristic that shortens the back focus of the objective lens when the oscillation wavelength of the incident light source slightly fluctuates to the long wavelength side, Axial chromatic aberration can be corrected satisfactorily. Furthermore, this diffractive surface has a spherical aberration characteristic that causes the spherical aberration of the objective lens to be undercorrected when the oscillation wavelength of the light source slightly fluctuates to the long wavelength side, so that the oscillation wavelength of the light source is on the long wavelength side. It is also possible to correct spherical aberration when a slight fluctuation occurs. Further, 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 also 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. Both the positive lens and the negative lens preferably have an Abbe number of 40.0 or more and 70.0 or less.

The beam expander according to claim 121, wherein a paraxial power at an oscillation wavelength of a light source that outputs an incident light beam is P1, a paraxial power at a wavelength 10 nm shorter than the oscillation wavelength is P2, and a wavelength 10 nm longer than the oscillation wavelength. When the paraxial power at is P3, the following equation is satisfied.
P2 <P1 <P3 (17)
Thereby, the beam expander can be given a role of correcting axial chromatic aberration generated in an optical element such as an objective lens or a coupling lens. That is, the diffractive structure overcorrects axial chromatic aberration in the beam expander itself, and generates axial chromatic aberration having a polarity opposite to that of axial chromatic aberration generated in an optical element such as an objective lens or a coupling lens. Axial chromatic aberration generated in an optical element such as a lens or a coupling lens can be corrected.

  The beam expander according to claim 122, wherein the diffractive surface suppresses on-axis chromatic aberration generated in a condensing lens arranged on the exit side with respect to minute fluctuations in an oscillation wavelength of a light source that outputs an incident light beam. It has a function.

  The beam expander according to claim 123, wherein when the oscillating wavelength of the light source that outputs the incident light beam slightly fluctuates toward the long wavelength side, the back focus of the condenser lens disposed on the output side is short. It is characterized by having such a wavelength characteristic. Thereby, axial chromatic aberration of an optical element such as an objective lens can be corrected well.

  The beam expander according to claim 124, wherein the diffractive surface corrects spherical aberration of the condensing lens arranged on the exit side when the oscillation wavelength of the light source that outputs the incident light beam slightly fluctuates to the long wavelength side. It has a characteristic of spherical aberration that changes in a direction that becomes insufficient. This makes it possible to satisfactorily correct spherical aberration when the oscillation wavelength of the light source that outputs the input light flux slightly fluctuates to the long wavelength side.

  A beam expander according to a 125th aspect is characterized in that the movable element is made of a material having a specific gravity of 2.0 or less. Thereby, the burden to the displacement apparatus of a movable element can be reduced.

  The beam expander according to claim 126 is characterized in that the movable element is made of a plastic material. As a result, it is possible to reduce the burden on the shift device, and it is possible to move the movable element in the optical axis direction at high speed. Furthermore, if the components providing the diffractive surface and the aspherical surface are formed from a plastic material, they can be easily added.

  The beam expander according to a 127th aspect is characterized in that at least one surface of the movable element has an aspherical surface.

  The beam expander according to claim 128 is characterized in that the movable element is made 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 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 an incident light source. To do.

  The beam expander according to claim 130 is made of a plastic material.

  The beam expander according to claim 131 is characterized in that at least one surface has an aspherical surface.

  The beam expander according to claim 132 is formed of a material having a saturated water absorption rate of 0.5% or less.

  The beam expander according to claim 133 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 an incident light source.

  A beam expander according to a thirteenth aspect is applicable to the optical pickup device according to any one of the eighth to thirty-third and thirty-sixth to thirty-sixth aspects.

  The diffractive surface used in this specification 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, so that the angle of the light beam is changed by diffraction. When there is a region where diffraction occurs on one optical surface and a region where it does not occur, the 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 each annular zone is shaped like a sawtooth if the cross section is viewed in a plane including the optical axis. Are known, but include such shapes. In particular, such a sawtooth ring zone structure is preferable.

  In this specification, the objective lens is, in a narrow sense, a light collecting action that is arranged to face the optical information recording medium at the position closest to the optical information recording medium when the optical information recording medium is loaded in the optical pickup device. 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, and is disposed between the light source and the objective lens, and is a coupling lens (incident incident) for converting the incident light beam into a substantially parallel light beam. Including a collimator that makes a divergent light beam a parallel light beam. However, it is an assembly of at least optical elements that function integrally, such as a beam expander, which will be described later, and an assembly in which some of the optical elements constituting the assembly can be displaced along the optical axis direction, and Here, a part of the optical elements of the aggregate is not included in the condensing optical system. The coupling lens may be composed of a plurality of lenses, or may be configured such that these lenses are spaced apart and another optical element is interposed therebetween.

  In this specification, a beam expander can change an optical element such as at least one lens along the optical axis direction, thereby making it possible to vary the divergence angle (including divergence and convergence) of the emitted light beam. An assembly of optical elements such as a lens (an optical element group such as a lens group) capable of emitting a substantially parallel light beam when a substantially parallel light beam is incident thereon. It is preferable that a plurality of optical elements such as these lenses are integrated, and if at least one optical element such as a lens is configured to be capable of shifting along the optical axis direction, the transition is actually performed. The driving means such as the shifting device to be performed may not be included as a beam expander.

  In the present specification, the means for correcting the variation of spherical aberration and the axial chromatic aberration is a single means, for example, a single optical means, for correcting the variation of spherical aberration and for correcting the axial chromatic aberration. This means that the device and its aggregate (for example, a beam expander) have both of two correction functions, for example, a beam composed of a positive lens and a negative lens having a specific Abbe number. Examples thereof include an expander and a beam expander having a surface having a diffractive structure. In this specification, in the invention related to the optical pickup device, unless otherwise specified, the focal length is the focal length of the light source that emits the light having the shortest oscillation wavelength among the light sources used. Shall be pointed to.

  In this specification, the minute fluctuation of the oscillation wavelength of the light source refers to a wavelength fluctuation within a range of ± 10 nm with respect to the oscillation wavelength of the light source. Further, in this specification, correcting various aberrations (good) means that the wavefront aberration is 0.07λ rms or less, which is a so-called diffraction-limited performance (where λ is the oscillation wavelength of the light source used). Further, it is more preferable that it is 0.05λrms or less in consideration of mechanical accuracy on the apparatus. Accordingly, appropriate spot sizes can be obtained for various optical information recording media.

  In this specification, as an optical information recording medium (optical disk), for example, various CDs such as CD-R, CD-RW, CD-Video, CD-ROM, DVD-ROM, DVD-RAM, DVD-R, Various DVDs such as DVD-RW and DVD-Video, and disk-like current optical information recording media such as MD 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, there is no transparent substrate.

  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. The optical pickup device of the present invention may be used only for recording or reproduction, or may be used for both recording and reproduction. Further, it may be used for recording with respect to a certain optical information recording medium and for reproducing with respect to another optical information recording medium, or with respect to a certain optical information recording medium. May be used for recording or reproduction, and recording and reproduction for another optical information recording medium. Note that reproduction here also includes simply reading information.

  The optical pickup device of the present invention can be mounted on audio and / or image recording and / or reproducing devices of various players or drives, or AV equipment, personal computers, and other information terminals in which they are incorporated.

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

It is a schematic block diagram of the optical pick-up apparatus concerning this Embodiment. 2 is a configuration diagram of an optical system of a negative lens 5, a positive lens 4, and an objective lens 3 according to Example 1. FIG. FIG. 3 is a spherical aberration diagram concerning the objective lens 3 according to the optical system of Example 1. FIG. 6 is an optical system configuration diagram of a negative lens 5, a positive lens 4, and an objective lens 3 according to Example 2. FIG. 6 is a spherical aberration diagram concerning the objective lens 3 according to the optical system of Example 2. FIG. 4 is an optical system configuration diagram of a negative lens 5, a positive lens 4, and an objective lens 3 according to Example 3. FIG. 6 is a spherical aberration diagram concerning the objective lens 3 according to the optical system of Example 3. FIG. 6 is an optical system configuration diagram of a negative lens 5, a positive lens 4, and an objective lens 3 according to Example 4. FIG. 6 is an optical system configuration diagram of a negative lens 5, a positive lens 4, and an objective lens 3 according to Example 4. FIG. 10 is a spherical aberration diagram concerning the objective lens 3 according to the optical system of Example 4; FIG. 10 is a spherical aberration diagram concerning the objective lens 3 according to the optical system of Example 4; FIG. 6 is an optical system configuration diagram of a negative lens 5, a positive lens 4, and an objective lens 3 according to Example 5. FIG. 6 is an optical system configuration diagram of a negative lens 5, a positive lens 4, and an objective lens 3 according to Example 5. FIG. 10 is a spherical aberration diagram concerning the objective lens 3 according to the optical system of Example 5. FIG. 10 is a spherical aberration diagram concerning the objective lens 3 according to the optical system of Example 5. FIG. 6 is an optical system configuration diagram of a negative lens 5, a positive lens 4, and an objective lens 3 according to Example 6. FIG. 12 is a spherical aberration diagram concerning the objective lens 3 according to the optical system of Example 6; FIG. 10 is an optical system configuration diagram of a negative lens 5, a positive lens 4, and an objective lens 3 according to Example 7. FIG. 12 is a spherical aberration diagram concerning the objective lens 3 according to the optical system of Example 7. FIG. 10 is an optical system configuration diagram of a negative lens 5, a positive lens 4, and an objective lens 3 according to an eighth embodiment. FIG. 12 is a spherical aberration diagram concerning the objective lens 3 according to the optical system of Example 8; FIG. 10 is an optical system configuration diagram of a negative lens 5, a positive lens 4, and an objective lens 3 according to Example 9. FIG. 12 is a spherical aberration diagram concerning the objective lens 3 according to the optical system of Example 9; FIG. 12 is an optical system configuration diagram of a negative lens 5, a positive lens 4, and an objective lens 3 according to Example 10. FIG. 12 is a spherical aberration diagram concerning the objective lens 3 according to the optical system of Example 10; FIG. 12 is an optical system configuration diagram of a negative lens 5, a positive lens 4, and an objective lens 3 according to Example 10. FIG. 12 is an optical system configuration diagram of a negative lens 5, a positive lens 4, and an objective lens 3 according to Example 11. FIG. 12 is a spherical aberration diagram concerning the objective lens 3 according to the optical system of Example 11; FIG. 12 is a configuration diagram of an optical system of a negative lens 5, a positive lens 4, and an objective lens 3 according to Example 12. FIG. 12 is a configuration diagram of an optical system of a negative lens 5, a positive lens 4, and an objective lens 3 according to Example 12. FIG. 22 is a spherical aberration diagram concerning the objective lens 3 according to the optical system of Example 12; FIG. 22 is a spherical aberration diagram concerning the objective lens 3 according to the optical system of Example 12; FIG. 15 is a configuration diagram of an optical system of a collimator, a negative lens 5, a positive lens 4, and an objective lens 3 according to Example 13. FIG. 20 is a spherical aberration diagram concerning the objective lens 3 according to the optical system of Example 13; FIG. 16 is a configuration diagram of an optical system of a collimator, a negative lens 5, a positive lens 4, and an objective lens 3 according to Example 14. FIG. 22 is a spherical aberration diagram concerning the objective lens 3 according to the optical system of Example 14; It is a figure which shows the optical system concerning different embodiment. It is a figure which shows the optical system concerning the modification of this Embodiment. FIG. 4 is a cross-sectional view (a) schematically showing an objective lens 3 ′ usable in the optical pickup device of the present embodiment, and a front view (b) seen from the light source side.

The aspheric surface used in the present embodiment is expressed by the following [Equation 1]. Here, x is an axis in the optical axis direction, h is an axis perpendicular to the optical axis, and the light traveling direction is positive, r is a paraxial radius of curvature, κ is a conic coefficient, and A _2i is an aspheric coefficient.

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

  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. In FIG. 1, a first light source 11 that performs recording and / or reproduction with respect to a first optical information recording medium 23, and a first light source 11 that performs recording and / or reproduction with respect to a second optical information recording medium 24. And a second light source 12 having different wavelengths, coupling lenses 21 and 22 for converting the divergence angles of divergent light beams emitted from the respective light sources into desired divergence angles, and substantially the light beams from the respective light sources. A beam splitter 62 which is an optical path combining means for traveling in 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 reflection from the optical information recording medium Photodetectors 41 and 42 for receiving light are provided. In the figure, 8 is a stop, 9 is a cylindrical lens, 71 and 72 are quarter-wave plates, 15 is a coupling lens for reducing the divergence of a divergent light beam from the light source 11, 16 is a concave lens, and 17 is a reflected light beam. It is a hologram for separating.

  Further, in the present embodiment, a negative lens 5, a positive lens 4, and an actuator 7 which are arranged in order from the light source side are provided as means for correcting the variation of spherical aberration of the objective lens 3 and divergence changing means. (Hereinafter also referred to as spherical aberration correcting means and divergence changing means). The actuator 7 functions as a shift 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. In addition, in Examples 1 to 14 showing a specific part of the optical system in relation to the present embodiment, a so-called beam expander composed of the shiftable negative lens 5 and positive lens 4 is used. One example may be expressed as spherical aberration correction means. Reference numeral 6 denotes an actuator for driving the objective lens 3 in the optical axis direction for focusing. It is assumed that the first light source 11 can emit laser light having a wavelength λ1 = 405 nm, and the second light source 12 can emit laser light having a wavelength λ2 = 655 nm.

  In Examples described below, Examples 1, 2, 11, and 12 are provided with a diffractive surface on the objective lens 3 to correct axial chromatic aberration, and Examples 3 to 5 are negative lens 5 and positive lens 4. The axial chromatic aberration of the objective lens 3 is corrected by providing a diffractive surface on at least one of the negative lens 5 and the positive lens 4 in Examples 6 to 8, 13, and 14. In Examples 9 and 10, the axial chromatic aberration of the objective lens 3 is corrected by the synergistic effect of the specific material of the negative lens 5 and the positive lens 4 and the diffraction surface provided on the positive lens 4. . Examples 4, 5, and 12 are examples in which information is recorded or reproduced on different optical information recording media using the same optical system. In the following objective lens embodiments, 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 used. Formed using. Further, in the following example, in the example using only the first light source 11 in the present embodiment shown in FIG. 1, the drawings of the specific embodiment are omitted, but generally in the pickup apparatus of FIG. For example, the second light source 12, the coupling lens 22, the beam splitter 62, the photodetector 42, the quarter wavelength plate 72, and the hologram 17 may be removed. Each example will be described below.

Example 1
Table 1 shows data related to the optical system including the negative lens 5, the positive lens 4, and the objective lens 3 in Example 1. In the lens data shown here, a power of 10 (for example, 2.5 × 10 ⁻³ ) is expressed using E (for example, 2.5 × E−3). Further, the first-order light generated by diffraction on the diffraction surface represented by a rotationally symmetric polynomial means light whose angle of light changes in the direction of convergence after diffraction.

  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. 3 is a spherical aberration diagram concerning the objective lens 3. In the first 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 0.85 of the objective lens 3. In the present embodiment, materials of νdN = 23.8 and νdP = 81.6 are selected as materials of the negative lens 5 and the positive lens 4 of the means for correcting the variation of the spherical aberration, respectively. By providing a diffractive surface on the light source side surface, axial chromatic aberration generated in the objective lens 3 is corrected. In this embodiment, fN = −8.13 (mm), fP = 9.48 (mm), f = 1.765 (mm), and fD = 71.383 (mm).

  In this embodiment, correction of minute fluctuations in the oscillation wavelength of the light source (hereinafter also simply referred to as wavelength fluctuations) or fluctuations in spherical aberration at the time of temperature changes can be performed as follows. In this embodiment, overcorrected spherical aberration occurs in the objective lens 3 when the wavelength increases or when the temperature rises. In such a case, if the gap between the negative lens 5 and the positive lens 4 is reduced by moving the negative lens 5 along the optical axis by the actuator 7 with respect to the generated spherical aberration, an undercorrected 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 apparent from Table 2 showing the correction result of the spherical aberration.

(Example 2)
Table 3 shows data related to the optical system including the negative lens 5, the positive lens 4, and the objective lens 3 in Example 2.

  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. 5 is a spherical aberration diagram concerning the objective lens 3. In the second 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 0.85 of the objective lens 3. In Example 2, materials of νdN = 30.0 and νdP = 56.5 are selected as materials of the negative lens 5 and the positive lens 4 of the means for correcting the variation of the spherical aberration, respectively, and the light source of the objective lens 3 is further selected. By providing a diffractive surface on the side surface, axial chromatic aberration generated in the objective lens 3 is corrected. In this embodiment, fN = −4.75 (mm), fP = 6.47 (mm), f = 1.765 (mm), and fD = 71.383 (mm).

  The correction of the variation of the spherical aberration at the time of the wavelength variation or the temperature variation in this embodiment is the same as that in the first embodiment, and thus the description thereof is omitted. As is apparent from Table 4 showing the correction result of the spherical aberration, the spherical aberration at the time of wavelength variation or temperature change is good. Further, by using plastic materials for the negative lens 5 and the positive lens 4 as means for correcting fluctuations in the objective lens 3 and spherical aberration, the weight of the optical system is reduced and the burden on the movable mechanism is reduced.

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

  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. 7 is a spherical aberration diagram concerning the objective lens 3. In the third 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 0.85 of the objective lens 3. In Example 3, axial 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), fP = 11.08 (mm), and f = 1.765 (mm).

  The correction of spherical aberration at the time of wavelength fluctuation or temperature change in the present embodiment is the same as that in the first embodiment, and thus description thereof is omitted. As is apparent from Table 6 showing the correction result of the spherical aberration, the spherical aberration at the time of wavelength fluctuation or temperature change is good. 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.

Example 4
Table 7 shows data related to the optical system including the negative lens 5, the positive lens 4, and the objective lens 3 in Example 4.

  8 and 9 are optical system configuration diagrams of the negative lens 5, the positive lens 4, and the objective lens 3 according to the fourth embodiment. 10 and 11 are spherical aberration diagrams concerning the objective lens 3 when information is recorded or reproduced on different optical information recording media. In Example 4, using the same optical system, a combination of a first light source 11 with a wavelength of 405 nm and an optical information recording medium with a transparent substrate thickness of 0.1 mm, or a second light source 11 with a wavelength of 655 nm, and a 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 Example 4, axial chromatic aberration is corrected by selecting materials of νdN = 30.0 and νdP = 56.5 as materials of the negative lens 5 and the positive lens 4, respectively. Further, in this embodiment, fN = −3.82 (mm), fP = 6.85 (mm), f1 = 1.765 (mm), and fD1 = 500000.02 (mm). Note that the focal length of the objective lens at the oscillation wavelength λ2 = 655 nm is f2 = 1.804.

  In the fourth embodiment, the variation in spherical aberration caused by the difference in the thickness of the transparent substrate in different optical information recording media is composed of one negative lens 5 and one positive lens 4 in order from the light source side. Correction is performed by changing the interval of 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 longitudinal chromatic aberration). Further, by providing a diffractive surface on the light source side surface of the objective lens 3, the spherical aberration is corrected more favorably. Furthermore, the spherical aberration deterioration of the objective lens when the light source wavelength is changed or when the temperature and humidity are changed is well corrected by changing the interval of the divergence changing means. That is, as apparent from Table 8, by changing the distance between the negative lens 5 and the positive lens 4 to an appropriate distance, the spherical aberration of the objective lens 3 is deteriorated when the substrate thickness is changed, the wavelength is changed, and the temperature and humidity are changed. Is corrected well. 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.

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

  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 spherical aberration diagrams concerning the objective lens 3 when information is recorded or reproduced on different optical information recording media, respectively. In Example 5, using the same optical system, a combination of a first light source 11 with a wavelength of 405 nm and an optical information recording medium with a transparent substrate thickness of 0.1 mm, or a second light source 11 with a wavelength of 655 nm, and a 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 Example 5, axial chromatic aberration is corrected by selecting materials of νdN = 30.0 and νdP = 56.5 as materials of the negative lens 5 and the positive lens 4, respectively. In this embodiment, fN = −6.59 (mm), fP = 9.85 (mm), f1 = 3.011 (mm), and fD1 = 849964.33 (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 distance between the negative lens 5 and the positive lens 4 to an appropriate distance, the objective at the time of changing the thickness of the transparent substrate, changing the wavelength, and changing the temperature and humidity is clear. The spherical aberration deterioration of the lens can be corrected well. 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.

  Note that the light beam incident on the negative lens 5 as a means for correcting the fluctuation of the spherical aberration is not only parallel light but also divergent light or convergent light as in the above-described embodiment, and the optical system of the present invention is used. Can be applied as well. Although not shown in the present embodiment, a coupling lens for changing the divergence of the light beam from the light source can be provided between the light source and the spherical aberration correcting means. By adding a diffractive surface to such a coupling lens so as to shorten the back focus on the long wavelength side, axial chromatic aberration generated in 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 form, and if it is as in Japanese Patent Application No. 2000-060843 by the same applicant, the axial chromatic aberration generated in the objective lens 3 is better. Can be corrected.

  Further, the astigmatic difference of the light beam from the light source is reduced between the coupling lens and the means for correcting the fluctuation of the spherical aberration (the negative lens 5 and the positive lens 4), and a substantially circular light beam is applied to the spherical aberration correcting means. When a beam shaping element that can be made incident is provided, the divergence of the light beam from the coupling lens changes due to the focal point movement of the coupling lens due to temperature and humidity changes, and astigmatism is generated by the beam shaping element. End up. In order to suppress this, astigmatism due to the beam shaping element can be suppressed by using a coupling lens as disclosed in Japanese Patent Application No. 2000-053858 by the same applicant.

  In Examples 4 and 5, aberration diagrams for optical information recording media having a light source wavelength of 655 nm and a transparent substrate thickness of 0.6 mm are shown up to NA 0.65. However, at this time, the objective lens 3 is incident with a light beam that passes through all the apertures determined by the light source wavelength of 405 nm and NA of 0.85. A light beam of NA 0.65 or more that does not contribute to image formation is used as a flare component by utilizing the effect of the diffractive 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 It is possible to prevent detection of unnecessary signals in the light receiving element.

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

  FIG. 16 is an optical system configuration diagram of the negative lens 5, the positive lens 4, and the objective lens 3 according to the sixth embodiment. FIG. 17 is a spherical aberration diagram concerning 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 0.85 of the objective lens 3. In the sixth embodiment, a 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 short back focus on the long wavelength side. It is corrected. In this embodiment, fN = −5.03 (mm), fP = 6.81 (mm), and f = 1.765 (mm).

  The correction of the fluctuation of the light source wavelength or the variation of the spherical aberration when the temperature changes in this embodiment is the same as that in the first embodiment, and thus the description thereof is omitted. As can be seen from Table 12, 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.

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

  FIG. 18 is an optical system configuration diagram of the negative lens 5, the positive lens 4, and the objective lens 3 according to the seventh embodiment. FIG. 19 is a spherical aberration diagram concerning the objective lens 3. In Example 7, 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 0.85 of the objective lens 3. In Example 7, axial chromatic aberration of the objective lens 3 is corrected by adding a diffractive surface to both surfaces of the positive lens 4 and forming a diffractive lens that shortens the back focus on the long wavelength side. In this embodiment, fN = −4.89 (mm), fP = 5.83 (mm), and f = 1.765 (mm).

  The correction of the fluctuation of the light source wavelength or the variation of the spherical aberration when the temperature changes in this embodiment is the same as that in the first embodiment, and thus the description thereof is omitted. As can be seen from Table 14, the spherical aberration at the time of wavelength fluctuation 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.

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

  FIG. 20 is an optical system configuration diagram of the negative lens 5, the positive lens 4, and the objective lens 3 according to the eighth embodiment. FIG. 21 is a spherical aberration diagram concerning the objective lens 3. In Example 8, 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 0.85 of the objective lens 3. In the eighth embodiment, axial chromatic aberration of the objective lens 3 is corrected by adding diffractive surfaces 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. In this embodiment, fN = −5.54 (mm), fP = 7.42 (mm), and f = 1.765 (mm).

  Since correction of spherical aberration at the time of light source length fluctuation or temperature change in this embodiment is the same as that in Embodiment 1, description thereof is omitted. As is apparent from Table 16, the spherical aberration at the time of wavelength fluctuation 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.

Example 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 Example 9.

  FIG. 22 is an optical system configuration diagram of the negative lens 5, the positive lens 4, and the objective lens 3 according to the ninth embodiment. FIG. 23 is a spherical aberration diagram concerning 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 0.85 of the objective lens 3. In Example 9, a diffractive surface is added to the surface of the positive lens 4 on the side of the optical information recording medium, and a diffractive lens that shortens the back focus on the long wavelength side is used. It is corrected. Further, by selecting materials of N = 30.0 and P = 56.5 as materials of the negative lens 5 and the positive lens 4 of the spherical aberration correcting means, the axial chromatic aberration of the objective lens can be corrected more satisfactorily. ing. In this embodiment, fN = −4.15 (mm), fP = 5.91 (mm), and f = 1.765 (mm).

  The correction of the fluctuation of the light source wavelength or the variation of the spherical aberration when the temperature changes in this embodiment is the same as that in the first embodiment, and thus the description thereof is omitted. As is apparent from Table 18, 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.

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

  FIG. 24 is an optical system configuration diagram of the negative lens 5, the positive lens 4, and the objective lens 3 according to the tenth embodiment. FIG. 25 is a spherical aberration diagram concerning the objective lens 3. In Example 10, 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 NA0.85 of the objective lens 3. In Example 10, axial chromatic aberration of the objective lens 3 is corrected by adding a diffractive surface to both surfaces of the positive lens 4 and forming a diffractive lens that shortens the back focus on the long wavelength side. At this time, as shown in FIG. 25, the axial chromatic aberration of the combined system including the objective lens 3 and the negative lens 5 and the positive lens 4 serving as spherical aberration correcting means is overcorrected. The spherical aberration curve of the oscillation wavelength (405 nm) of one light source 11 and the spherical aberration curve on the long / short wavelength side are crossed. 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 very 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. Furthermore, the negative lens 5 that is a movable element as a spherical aberration correcting means is a double-sided aspheric lens, so that the decentering of the negative lens 5 and the deterioration of wavefront aberration at the time of tracking error are suppressed to a minimum. Further, the axial chromatic aberration of the objective lens 3 is corrected by selecting materials of νdN = 24.3 and νdP = 56.5 as materials of the negative lens 5 and the positive lens 4, respectively, and added to the positive lens 4. This reduces the burden on the diffractive structure. In this embodiment, fN = −7.78 (mm), fP = 9.95 (mm), and f = 1.765 (mm).

  In the present embodiment, the diaphragm for restricting the light beam is disposed on the optical information recording medium side from the apex of the surface on the light source side of the objective lens 3, so that when the divergent light beam is incident, the most light source side of the objective lens 3. The height of light passing through the surface can be kept small. This is preferable for reducing the diameter of the objective lens 3 or correcting aberrations.

  The correction of the fluctuation of the wavelength of the light source or the change of the spherical aberration at the time of the temperature change in this embodiment is the same as that in the first embodiment, and the description thereof will be omitted. As can be seen 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 with respect to light having a short wavelength is used, an optical system that can be mass-produced at low cost and has high light utilization efficiency has been achieved. Note that the movable mechanism is a shifting device for the negative lens 5 and a focusing mechanism for the objective lens 3 in the embodiments in this specification.

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

  Furthermore, the recording capacity of the optical information recording medium is substantially reduced by providing two phase change films of the first information recording layer and the second information recording layer on one side of the optical information recording medium and recording information on each of them. A so-called double-layer recording type optical information recording medium is known which is doubled. In this embodiment, information is recorded or reproduced on such a double-layer recording type optical information recording medium. The spherical aberration caused by the difference in thickness up to the information recording surface of each information recording layer can be corrected. For example, when the first information recording layer and the second information recording layer are sequentially formed 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 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.

(Example 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 Example 11.

  FIG. 27 is an optical system configuration diagram of the negative lens 5, the positive lens 4, and the objective lens 3 according to the eleventh embodiment. FIG. 28 is a spherical aberration diagram concerning the objective lens 3. In Example 11, 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 NA0.85 of the objective lens 3. In Example 11, a diffractive surface is added to the surface of the objective lens 3 on the light source side so that the back focus is shortened on the long wavelength side, thereby correcting the axial chromatic aberration of the objective lens 3. Yes. Furthermore, the negative lens 5 that is a movable element as a spherical aberration correcting means is a double-sided aspheric lens, so that the decentering of the negative lens 5 and the deterioration of wavefront aberration at the time of tracking error are suppressed to a minimum. In this example, fN = −8.32 (mm), fP = 12.30 (mm), f = 1.765 (mm), and fD = 28.417 (mm).

  The correction of the fluctuation of the wavelength of the light source or the change of the spherical aberration at the time of the temperature change in this embodiment is the same as that in the first embodiment, and the description thereof will be omitted. As apparent from Table 22, 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 with respect to light having a short wavelength is used, an optical system that can be mass-produced at low cost and has high light utilization efficiency has been achieved.

(Example 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 Example 12.

  29 and 30 are optical system configuration 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 spherical aberration diagrams concerning the objective lens 3 when information is recorded or reproduced on different optical information recording media, respectively. In Example 12, using the same optical system, a combination of a first light source 11 with a wavelength of 405 nm and an optical information recording medium with a transparent substrate thickness of 0.1 mm, or a second light source 11 with a wavelength of 655 nm, and a 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 diffractive structure on the surface of the objective lens 3 on the light source side, spherical aberration and chromatic spherical aberration caused by the difference in the thickness of the transparent substrate are corrected. Specifically, by moving the negative lens 5 as the spherical aberration correction means in the optical axis direction, the divergence angle of the light beam incident on the objective lens 3 is changed corresponding to the transparent substrate thickness of the optical information recording medium. Do. In this embodiment, fN = −6.39 (mm), fP = 10.51 (mm), f1 = 1.765 (mm), and fD1 = 45.46 (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 fluctuation of the wavelength of the light source or the change of the spherical aberration at the time of the temperature change in this embodiment is the same as that in the first embodiment, and the description thereof will be omitted. As is apparent 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. In addition, since a plastic material having a high transmittance with respect to light having a short wavelength is used, an optical system that can be mass-produced at low cost and has high light utilization efficiency has been achieved.

  As in Examples 4 and 5, a light flux of NA 0.65 or more with respect to an optical information recording medium having a light source wavelength of 655 nm and a transparent substrate thickness of 0.6 mm flare using the effect of the diffractive surface provided on the objective lens 3. By using the component, the spot diameter is not excessively reduced on the information recording surface, and detection of an unnecessary signal at the light receiving element of the optical pickup device can be prevented.

(Example 13)
Table 25 shows data related to the optical system including the collimator corresponding to the coupling lens 21 or the coupling lenses 15 and 21, the negative lens 5, the positive lens 4, and the objective lens 3 in Example 13.

  FIG. 33 is an optical system configuration diagram of the collimator, the negative lens 5, the positive lens 4, and the objective lens 3 according to the thirteenth embodiment. FIG. 34 is a spherical aberration diagram concerning the objective lens 3. In Example 13, 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 0.85 of the objective lens 3. In the thirteenth embodiment, the negative lens 5 in the spherical aberration correcting means is shifted along the optical axis direction, thereby changing the divergence angle of the light beam incident on the objective lens 3, and the condensing optical system (collimator and objective lens). The variation of spherical aberration occurring on each optical surface in 3) is corrected. In this embodiment, fN = -10.71 (mm), fP = 13.18 (mm), and f = 1.765 (mm).

  Further, by adding diffractive surfaces to both surfaces of the positive lens 4, the spherical aberration correcting means itself generates axial chromatic aberration having a polarity opposite to the axial chromatic aberration generated on the optical surface of the condensing optical system, thereby condensing light. The axial chromatic aberration generated on the optical surface of the optical system was corrected to improve the axial chromatic aberration of the wavefront when focused on the information recording surface. In the condensing optical system of this example, when the axial chromatic aberration amounts generated by the collimator and the objective lens 3 as the optical elements are respectively ΔfB1 and ΔfB2, and the ratios thereof are roughly calculated, the focal length of the collimator is Since 12 mm, the magnification of the spherical aberration correction means is 1.23 times, and the distance between the objective lenses is 1.765 mm, ΔfB1 / ΔfB2 = 1/30. That is, if the absolute value of the axial chromatic aberration of the reverse polarity generated by the spherical aberration correcting means is substantially the same as the absolute value of the axial chromatic aberration generated by the objective lens, the axis of the wavefront when focused on the information recording surface The upper chromatic aberration can be improved. At this time, as shown in FIG. 34, the axial chromatic aberration of the combined system that combines the condensing optical system and the negative lens 5 and the positive lens 4 as spherical aberration correcting means is overcorrected. The spherical aberration curve of the oscillation wavelength (405 nm) of the first light source 11 and the spherical aberration curve on the long / short wavelength side are crossed. 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 very 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. Further, the negative lens 5 which is a movable element in the spherical aberration correcting means is a double-sided aspheric lens, so that the decentering of the negative lens 5 and the deterioration of the wavefront aberration at the time of tracking error are suppressed to a minimum.

  As can be seen from Table 26, the variation of spherical aberration that occurs on each optical surface of the condensing optical system can be corrected due to various factors, such as when the wavelength varies or when the temperature varies, resulting in good spherical aberration. Further, by using plastic materials for all of the collimator and 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. We are trying to reduce the burden. In addition, since a plastic material having a high transmittance with respect to light having a short wavelength is used, an optical system that can be mass-produced at low cost and has high light utilization efficiency has been achieved.

  In this embodiment, the negative lens 5 in the spherical aberration correcting means can be shifted. However, the positive lens 4 may be movable, and both the lenses can be shifted. The variation of the spherical aberration can be corrected. In this embodiment, the axial chromatic aberration of the condensing optical system and the spherical aberration correcting means is corrected by the diffractive structure provided on the positive lens 4 in the spherical aberration correcting means. Alternatively, an optical element having a surface provided with a diffractive structure may be separately added.

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

  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 the fourteenth embodiment. 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 is a spherical aberration diagram concerning the objective lens 3. In Example 14, 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 NA0.85 of the objective lens 3. In the fourteenth embodiment, the negative lens 5 in the spherical aberration correcting means is shifted along the optical axis direction, thereby changing the divergence angle of the light beam incident on the objective lens 3, and the condensing optical system (coupling lens 15). And variations in spherical aberration occurring on each optical surface of the objective lens 3) are corrected. In this embodiment, fN = -14.67 (mm), fP = 11.66 (mm), and f = 1.765 (mm).

  Further, by adding diffractive surfaces to both surfaces of the positive lens 4, the spherical aberration correcting means itself generates axial chromatic aberration having a polarity opposite to the axial chromatic aberration generated on the optical surface of the condensing optical system, thereby condensing light. The axial chromatic aberration generated on the optical surface of the optical system was corrected to improve the axial chromatic aberration of the wavefront when focused on the information recording surface. At this time, as shown in FIG. 36, the axial chromatic aberration of the combined system combining the condensing optical system and the negative lens 5 and the positive lens 4 as spherical aberration correcting means is overcorrected. The spherical aberration curve of the oscillation wavelength (405 nm) of the first light source 11 and the spherical aberration curve on the long / short wavelength side are crossed. 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 very 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 apparent from Table 28, the spherical aberration variation generated on each optical surface of the condensing optical system can be corrected due to various factors such as the wavelength variation or the temperature variation, and the spherical aberration is satisfactory. Further, the plastic lens is used 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, thereby reducing the weight and moving the optical system. The burden on the mechanism is reduced. In addition, since a plastic material having a high transmittance with respect to light having a short wavelength is used, an optical system that can be mass-produced at low cost and has high light utilization efficiency has been achieved. Further, in this embodiment, since the incident light to the spherical aberration correction 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 correction means can be reduced, and each lens can be reduced. Deterioration of wavefront aberration due to decentration of the lens was suppressed to a small level.

  In this embodiment, the negative lens 5 in the spherical aberration correcting means can be shifted. However, the positive lens 4 may be movable, and both the lenses can be shifted. The variation of the spherical aberration can be corrected. In this embodiment, the axial chromatic aberration of the condensing optical system and the spherical aberration correcting means is corrected by the diffractive structure provided on the positive lens 4 in the spherical aberration correcting means. Alternatively, an optical element having a surface provided with a diffractive structure may be separately added.

  Each example illustrated above uses a beam expander as a spherical aberration correction means, and the beam expander shows an example constituted by a displaceable single lens negative lens and a single lens positive lens. However, it is needless to say that the present invention is not limited to this, and may be configured by two or more lens groups including a plurality of lenses, and various modifications are possible without departing from the present invention.

  FIG. 37 is a diagram showing optical systems according to different embodiments. An element SE that corrects the variation of spherical aberration is inserted between the coupling lens CL and the objective lens OL. Such an optical system can be used in place of the negative lens 5, the positive lens 4, and the objective lens 3 of FIG.

  The element SE sandwiches the X-direction liquid crystal element SE1, the half-wave plate SE2, and the Y-direction liquid crystal element SE3 from the coupling glass CL side between the four glass plates SE4. By electrically driving both liquid crystal elements SE1 and SE2, it is possible to correct variations in spherical aberration. Further, by providing an annular diffractive structure (not shown) on the surface of the coupling lens CL on the objective lens side, the chromatic aberration having the opposite phase to the axial chromatic aberration generated in the objective lens OL, that is, over the short wave town side. On the long wavelength side, under-axial chromatic aberration can be generated. As a result, since the axial chromatic aberration is canceled, the wavefront when passing through the element SE that corrects the variation of the spherical aberration and the objective lens OL and focusing on the optical information recording medium (not shown) is The bearing chromatic aberration is reduced.

  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 variation of the spherical aberration are the same as those in 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 together, and the Abbe number νdN of the negative lens CL1 and the Abbe number νdP of the positive lens CL2 are νdN <νdP. The relationship is established.

  By adjusting the Abbe numbers of the negative lens CL1 and the positive lens CL2 in this way, the chromatic aberration of the opposite phase to the axial chromatic aberration generated in the objective lens OL, that is, the axis on the short wave side is over and the axis on the long wavelength side is under. Chromatic aberration can be generated. As a result, since the axial chromatic aberration is canceled, the wavefront when passing through the element SE that corrects the variation of the spherical aberration and the objective lens OL and focusing on the optical information recording medium (not shown) is The bearing chromatic aberration is reduced.

    FIG. 39 is a cross-sectional view (a) schematically showing an objective lens 3 ′ that can be used in the optical pickup device of the present embodiment and a front view (b) as seen from the light source side. The axis is shown].

  This objective lens 3 ′ can correct spherical aberration variation due to the difference in thickness of the transparent substrate of different optical information recording media. In FIG. 36, the light source side refractive surface S1 and the optical disk side refractive surface S2 are both convex lenses having an aspherical shape and having positive refractive power. Further, the refractive 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 of the dividing surface is provided with a step to form each dividing surface. Accordingly, the spherical aberration and the wavefront aberration of the objective lens have a step at a position corresponding to the boundary portion.

  In a normal objective lens, the occurrence of spherical aberration due to the difference in the transparent substrate thickness of different optical information recording media is inevitable. However, although the objective lens 3 ′ used in the present embodiment cannot perform complete spherical aberration correction, it is designed to relax such aberration as will be described below.

  First, when information is reproduced and / or recorded on the first optical information recording medium, the refractive surface S1 and the refractive surface S2 so that the spherical aberration component of the wavefront aberration is within 0.05λ1 rms at the best image plane position. To design. The refracting surface S1 thus designed is applied to the first divided surface b1 and the fourth divided surface b4. A new refracting surface S1 ′ is used without using the refracting 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 the transparent substrate thickness t3 (t1 ≦ t3 ≦ t2). To design.

  The refracting surface S1 ′ is the second divided surface b2 and the third divided surface b3. Since the refractive surface S1 ′ is optimized by the transparent substrate thickness t3, 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 fourth divided plane b4. However, the wavefront aberration changes the inclination of the wavefront aberration in the dividing plane. For example, in the first optical information recording medium (for example, a next-generation optical disk having a higher density and a larger capacity than the DVD), the wavefront aberration drops to the right. On the contrary, in the second optical information recording medium (for example, DVD), it is slightly increased. Providing a part of two or more such dividing surfaces on the refracting surface S1 facilitates coexistence of wavefront aberrations in different optical information recording media.

  By appropriately designing the boundary positions of these divided surfaces and the axial thicknesses of the divided surfaces, the wave front at the minimum beam spot circle of confusion and the front pin position on the DVD for next-generation optical disks with higher density and larger capacity than DVD. Aberration correction is possible. That is, in a next-generation optical disk having a higher density and a larger capacity than DVD, the light beam in the first to fourth light beams LB1 to LB4 is condensed at the position of the minimum circle of confusion by the objective lens. The wavefront aberration is an integral multiple of λ1, that is, miλ1 (mi is an integer and i = 1, 2,..., k).

  Further, since the required numerical aperture NA2 is smaller than NA1 in DVD, it is not necessary to effectively use all of the first to fourth light beams LB1 to LB4. In the optical pickup device of the present embodiment, the first to third light beams LB1 to LB1 are not necessary. The light beam in the LB3 has a wavefront aberration of approximately the integral multiple niλ1 (ni is an integer, i = 1, 2,..., K) of the wavelength λ2 at the front pin position. The fourth light beam LB4 is unnecessary light in the case of DVD, and is irradiated as a flare on a recording surface of the optical disc at a position spaced from the main spot light. Since this flare is sufficiently small with respect to the main spot light, a means for changing the numerical aperture of the diaphragm 8 is required only by making the diaphragm 8 equivalent to the required numerical aperture of a next-generation optical disk having a higher density and larger capacity than DVD. DVD playback is possible. Of course, a diaphragm 8 having a function of shielding the fourth light beam LB4 when using a DVD may be used.

  Therefore, although the optical pickup device of the present embodiment is provided with four divided surfaces b1 to b4, unlike the objective lens of the prior art, each disk does not have a plurality of focal positions, so that it is possible to reduce the spot light amount loss. And, when using each optical disk, the wavefront aberration of the light beam within the required numerical aperture is made an integer multiple of the wavelength, and the light beams that have passed through the required numerical aperture interfere with each other and strengthen each other. A sufficient amount of reflected light can be obtained from the optical disc, and a stable operation can be performed as a compatible optical pickup device.

  In the present embodiment, the objective lens is provided with four dividing surfaces, but basically has three portions for dividing the incident light beam into three light beams so as to form three dividing surfaces. An objective lens having a surface can also be used for the objective lens 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 the optical axis side toward the outer periphery thereof on at least one surface The first part and the third part are from a light source so that information can be recorded on or reproduced from the information recording surface of the first optical information recording medium having a transparent substrate thickness t1. Of the first optical information recording surface of the second optical information recording medium having a transparent substrate thickness t2 (t1 <t2). This is a well-known objective lens configured to be able to collect a light beam from a light source on an information recording surface so that information can be recorded or reproduced.

  According to the present embodiment described above, the optical pickup device and the optical system that can effectively correct the variation of the spherical aberration caused by the mode hop of the semiconductor laser, the spherical aberration of the objective lens caused by the temperature / humidity change, etc. An optical pickup device and an optical system capable of effectively correcting fluctuations, an optical pickup device including a short wavelength laser and a high NA objective lens and capable of recording or reproducing information on different optical information recording media can be provided. . Of course, the present invention is not limited to the above embodiment and various examples.

DESCRIPTION OF SYMBOLS 3 Objective lens 4 Positive lens 5 Negative lens 6 Actuator of objective lens 7 Actuator of negative lens 8 Aperture 9 Cylindrical lens 11 1st light source 12 2nd light source 15 Coupling lens 16 Concave lens 17 Hologram 21 Coupling lens 41, 42 Photo detector 62 Beam splitter 71, 72 1/4 wavelength plate

Claims (134)

A 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 the optical information recording medium, and reflected light from the optical information recording medium An optical pickup device having a photodetector for receiving light,
The objective lens includes at least one lens made of a plastic material,
A change in at least one of the shape and refractive index of the objective lens and the light source with respect to an environmental change between −30 ° C. to + 85 ° C. and a humidity of 5% to 90% between the light source and the objective lens. An optical pickup device provided with means for correcting fluctuations in spherical aberration caused by fluctuations in oscillation wavelength. A light source having an oscillation wavelength λ, a condensing optical system including an objective lens for condensing a light beam emitted from the light source onto an information recording surface via a transparent substrate of the optical information recording medium, and the optical information recording medium An optical pickup device having a photodetector for receiving reflected light from
Provided between the light source and the objective lens is a means for correcting the variation of spherical aberration,
The optical pickup device characterized in that the means for correcting the fluctuation of the spherical aberration can correct the spherical aberration up to 0.2λrms to 0.07λrms or less.   3. The optical pickup device according to claim 2, wherein the means for correcting the variation of the spherical aberration can correct the spherical aberration up to 0.5λrms to 0.07λrms or less. A 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 the optical information recording medium, and reflected light from the optical information recording medium An optical pickup device having a photodetector for receiving light,
An optical pickup device comprising means for correcting a variation in spherical aberration generated in the objective lens between the light source and the objective lens. A 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 the optical information recording medium, and reflected light from the optical information recording medium An optical pickup device having a photodetector for receiving light,
An optical pickup device comprising means for correcting a variation in spherical aberration generated in the objective lens due to a minute variation in the oscillation wavelength of the light source between the light source and the objective lens. A 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 the optical information recording medium, and reflected light from the optical information recording medium An optical pickup device having a photodetector for receiving light,
An optical pickup device comprising means for correcting 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. A 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 the optical information recording medium, and reflected light from the optical information recording medium An optical pickup device having a photodetector for receiving light,
Means is provided between the light source and the objective lens for correcting a variation in spherical aberration generated in the condensing optical system due to a minute variation in oscillation wavelength of the light source and a change in temperature and humidity. An optical pickup device.   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 that can be displaced in the optical axis direction. The optical pickup device according to claim 1.   The means for correcting the variation 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 having a negative refractive power, 8. The optical pickup device according to claim 1, wherein at least one of the lens groups is a movable element capable of shifting in the optical axis direction. 9. The optical pickup device according to claim 8, wherein the means for correcting the variation of the spherical aberration satisfies the following expression.
νdP> νdN
However,
νdP: average d-line Abbe number of all positive lenses including the positive lens νdN: average d-line Abbe number of all negative lenses including the negative lens The optical pickup device according to claim 9, wherein the means for correcting the variation of the spherical aberration satisfies the following expression.
νdP> νdN
However,
νdP: average d-line Abbe number of all positive lenses including the positive lens νdN: average d-line Abbe number of all negative lenses including the negative lens The optical pickup apparatus according to claim 10, wherein the νdP and the νdN satisfy the following expression.
νdP> 55
νdN <35 The optical pickup apparatus according to claim 11, wherein the νdP and the νdN satisfy the following expression.
νdP> 55
νdN <35 The following equation is established when the means for correcting the variation of the spherical aberration is constituted by a positive lens group including the positive lens and a negative lens group including the negative lens. 12. The optical pickup device according to 12.
Δd · | fP / fN | /Δνd≦0.05
However,
Δd: Amount of movement (mm) of the movable element when information is recorded or reproduced on one information recording surface of any one optical information recording medium capable of recording or reproducing information
fP: focal length (mm) of the positive lens group (however, when the positive lens group is provided with a diffractive surface, the total focal length combining the refractive power and the diffractive power)
fN: focal length (mm) of the negative lens group (however, when the positive lens group is provided with a diffractive surface, the total focal length combining the refractive power and the diffractive power)
Δνd: difference between the maximum Abbe number of the positive lens and the minimum Abbe number of the negative lens in the positive lens group and the negative lens group The optical pickup device according to claim 9, wherein the means for correcting the variation of the spherical aberration satisfies the following expression.
Δd · | fP / fN | /Δνd≦0.05
However,
Δd: Amount of movement (mm) of the movable element when information is recorded or reproduced on one information recording surface of any one optical information recording medium capable of recording or reproducing information
fP: focal length (mm) of the positive lens group (however, when the positive lens group is provided with a diffractive surface, the total focal length combining the refractive power and the diffractive power)
fN: focal length (mm) of the negative lens group (however, when the positive lens group is provided with a diffractive surface, the total focal length combining the refractive power and the diffractive power)
Δνd: difference between the maximum Abbe number of the positive lens and the minimum Abbe number of the negative lens in the positive lens group and the negative lens group The optical pickup device can record and / or reproduce information with respect to at least two types of optical information recording media.
The means for correcting the variation of the spherical aberration changes the divergence of the light beam incident on the objective lens according to the thickness of each transparent substrate with respect to at least two types of optical information recording media having different transparent substrate thicknesses. The optical pickup device according to claim 8, 10 or 12. The optical pickup device can record and / or reproduce information with respect to at least two types of optical information recording media.
The means for correcting the variation of the spherical aberration changes the divergence of the light beam incident on the objective lens according to the thickness of each transparent substrate with respect to at least two types of optical information recording media having different transparent substrate thicknesses. 16. The optical pickup device according to claim 9, wherein the optical pickup device is any one of the above. The optical pickup device is capable of recording and / or reproducing information with respect to an optical information recording medium in which a plurality of transparent substrates and information recording layers are laminated in order from the surface side of the optical information recording medium.
The means for correcting the fluctuation of the spherical aberration changes the divergence of the light beam incident on the objective lens according to the information recording layer when condensing each information recording layer. The optical pickup device according to 8, 10 or 12. The optical pickup device is capable of recording and / or reproducing information with respect to an optical information recording medium in which a plurality of transparent substrates and information recording layers are laminated in order from the surface side of the optical information recording medium.
The means for correcting the fluctuation of the spherical aberration changes the divergence of the light beam incident on the objective lens according to the information recording layer when condensing each information recording layer. The optical pickup device according to any one of 9, 11, 13 to 15.   When the transparent substrate thicknesses of the two types of optical information recording media are a and b (a <b), respectively, when information is recorded on or reproduced from the information recording surface of the optical information recording medium having the transparent substrate thickness a. The distance between the negative lens and the positive lens is increased as compared with the case where information is recorded on or reproduced from the information recording surface of the optical information recording medium having the transparent substrate thickness b. The optical pickup device described.   When the transparent substrate thicknesses of the two types of optical information recording media are a and b (a <b), respectively, when information is recorded on or reproduced from the information recording surface of the optical information recording medium having the transparent substrate thickness a. The method further comprises increasing the distance between the negative lens group and the positive lens group as compared to recording or reproducing information on the information recording surface of the optical information recording medium having the transparent substrate thickness b. 18. An optical pickup device according to item 17. 21. When the means for correcting the variation 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 expression is satisfied: The optical pickup device described in 1.
| FP / fN | ≧ 1.3
However,
fP: focal length of the positive lens group (however, when the positive lens group is provided with a diffractive surface, the total focal length combining the refractive power and the diffractive power)
fN: focal length of the negative lens group (however, when the negative lens group is provided with a diffractive surface, the total focal length combining the refractive power and the diffractive power) The optical pickup device according to claim 17, 19 or 21, wherein the following expression is satisfied.
| FP / fN | ≧ 1.3
However,
fP: focal length of the positive lens group (however, when the positive lens group is provided with a diffractive surface, the total focal length combining the refractive power and the diffractive power)
fN: focal length of the negative lens group (however, when the negative lens group is provided with a diffractive surface, the total focal length combining the refractive power and the diffractive power)   24. The optical pickup device according to claim 8, further comprising a shift device that shifts the movable element along an optical axis in accordance with a change in spherical aberration.   The optical pickup device according to any one of claims 8 to 24, wherein the movable element is made of a material having a specific gravity of 2.0 or less.   26. The optical pickup device according to claim 8, wherein at least one of the positive lens and the negative lens is made of a plastic material.   26. The optical pickup device according to claim 8, wherein the movable element is made of a plastic material.   The optical pickup device according to any one of claims 8 to 27, wherein at least one of the positive lens and the negative lens has an aspheric surface on at least one surface.   28. The optical pickup device according to claim 27, wherein at least one surface of the movable element has an aspheric surface.   30. The optical pickup device according to claim 8, wherein the means for correcting the variation of the spherical aberration is made of a material having a saturated water absorption rate of 0.5% or less.   The means for correcting the fluctuation of the spherical 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. 30. The optical pickup device according to any one of 30.   The optical pickup device according to any one of claims 8 to 31, wherein the means for correcting the variation of the spherical aberration includes the one positive lens and the one negative lens.   The optical pickup device according to any one of claims 8 to 32, wherein the means for correcting the variation of the spherical aberration includes an optical element having a diffractive surface having an annular diffractive structure.   8. The optical pickup device according to claim 1, wherein the means for correcting the variation of the spherical aberration includes an element capable of changing a refractive index distribution. A 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 the optical information recording medium, and reflected light from the optical information recording medium An optical pickup device having a photodetector for receiving light,
An optical pickup device comprising means for correcting a variation in spherical aberration generated in the objective lens and an axial chromatic aberration generated in the objective lens between the light source and the objective lens.   The means for correcting the variation of the spherical aberration and the longitudinal chromatic aberration includes at least one positive lens and at least one negative lens, at least one of which is a movable element that can be displaced in the optical axis direction. 36. The optical pickup device according to claim 35, wherein:   The means for correcting the variation of the spherical aberration and the axial chromatic aberration includes a positive lens group including one positive lens and having positive refractive power, and a negative lens including one negative lens and having negative refractive power. 36. The optical pickup device according to claim 35, wherein at least one of the lens groups is a movable element that is movable in the optical axis direction. The optical pickup device according to claim 36, wherein the means for correcting the variation of the spherical aberration and the longitudinal chromatic aberration satisfy the following equation.
νdP> νdN
However,
νdP: average d-line Abbe number of all positive lenses including the positive lens νdN: average d-line Abbe number of all negative lenses including the negative lens The optical pickup device according to claim 37, wherein the means for correcting the variation of the spherical aberration and the longitudinal chromatic aberration satisfy the following equation.
νdP> νdN
However,
νdP: average d-line Abbe number of all positive lenses including the positive lens νdN: average d-line Abbe number of all negative lenses including the negative lens The optical pickup device according to claim 38, wherein the νdP and the νdN satisfy the following expression.
νdP> 55
νdN <35 40. The optical pickup device according to claim 39, wherein the νdP and the νdN satisfy the following expression.
νdP> 55
νdN <35 When the means for correcting the variation 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. 41. The optical pickup device according to claim 36, 38 or 40.
Δd · | fP / fN | /Δνd≦0.05
However,
Δd: [Spherical aberration variation and axial chromatic aberration are corrected when information is recorded or reproduced on one information recording surface of an arbitrary optical information recording medium capable of recording or reproducing information. Movement amount of movable element (mm)
fP: focal length (mm) of the positive lens group (however, when the positive lens group is provided with a diffractive surface, the total focal length combining the refractive power and the diffractive power)
fN: focal length (mm) of the negative lens group (however, when the positive lens group is provided with a diffractive surface, the total focal length combining the refractive power and the diffractive power)
Δνd: difference between the maximum Abbe number of the positive lens and the minimum Abbe number of the negative lens in the positive lens group and the negative lens group 42. The optical pickup device according to claim 37, 39, or 41, wherein the means for correcting the variation of the spherical aberration and the longitudinal chromatic aberration satisfies the following expression.
Δd · | fP / fN | /Δνd≦0.05
However,
Δd: Amount of movement (mm) of the movable element when information is recorded or reproduced on one information recording surface of any one optical information recording medium capable of recording or reproducing information
fP: focal length (mm) of the positive lens group (however, when the positive lens group is provided with a diffractive surface, the total focal length combining the refractive power and the diffractive power)
fN: focal length (mm) of the negative lens group (however, when the positive lens group is provided with a diffractive surface, the total focal length combining the refractive power and the diffractive power)
Δνd: difference between the maximum Abbe number of the positive lens and the minimum Abbe number of the negative lens in the positive lens group and the negative lens group When the means for correcting the variation 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. 41. The optical pickup device according to claim 36, 38 or 40.
Δd · │fP / fN│ ≦ 0.50
However,
Δd: Amount of movement (mm) of the movable element when information is recorded or reproduced on one information recording surface of any one optical information recording medium capable of recording or reproducing information
fP: focal length (mm) of the positive lens group (however, when the positive lens group is provided with a diffractive surface, the total focal length combining the refractive power and the diffractive power)
fN: focal length (mm) of the negative lens group (however, when the positive lens group is provided with a diffractive surface, the total focal length combining the refractive power and the diffractive power)
Δνd: difference between the maximum Abbe number of the positive lens and the minimum Abbe number of the negative lens in the positive lens group and the negative lens group The optical pickup device according to any one of claims 37, 39, 41 to 43, wherein the means for correcting the variation of the spherical aberration and the longitudinal chromatic aberration satisfies the following expression.
Δd · │fP / fN│ ≦ 0.50
However,
Δd: Amount of movement (mm) of the movable element when information is recorded or reproduced on one information recording surface of any one optical information recording medium capable of recording or reproducing information
fP: focal length (mm) of the positive lens group (however, when the positive lens group is provided with a diffractive surface, the total focal length combining the refractive power and the diffractive power)
fN: focal length (mm) of the negative lens group (however, when the positive lens group is provided with a diffractive surface, the total focal length combining the refractive power and the diffractive power)
Δνd: difference between the maximum Abbe number of the positive lens and the minimum Abbe number of the negative lens in the positive lens group and the negative lens group The optical pickup device can record and / or reproduce information on at least two types of optical information recording media,
The means for correcting the variation of the spherical aberration and the longitudinal chromatic aberration is incident on the objective lens according to the thickness of each transparent substrate with respect to at least two types of optical information recording media having different transparent substrate thicknesses. 41. The optical pickup device according to claim 36, 38 or 40, wherein the divergence of the light beam is changed. The optical pickup device can record and / or reproduce information on at least two types of optical information recording media,
The means for correcting the variation of the spherical aberration and the longitudinal chromatic aberration is incident on the objective lens according to the thickness of each transparent substrate with respect to at least two types of optical information recording media having different transparent substrate thicknesses. The optical pickup device according to any one of claims 37, 39, 41 to 45, wherein the divergence of the light beam is changed. The optical pickup device is capable of recording and / or reproducing information with respect to an optical information recording medium in which a plurality of transparent substrates and information recording layers are laminated in order from the surface side of the optical information recording medium.
The means for correcting the variation of the spherical aberration and the axial chromatic aberration changes the divergence of the light beam incident on the objective lens according to the information recording layer when condensing each information recording layer. 41. The optical pickup device according to claim 36, 38, or 40. The optical pickup device is capable of recording and / or reproducing information with respect to an optical information recording medium in which a plurality of transparent substrates and information recording layers are laminated in order from the surface side of the optical information recording medium.
The means for correcting the variation of the spherical aberration and the axial chromatic aberration changes the divergence of the light beam incident on the objective lens according to the information recording layer when condensing each information recording layer. 46. The optical pickup device according to any one of claims 37, 39, 41 to 45.   When the transparent substrate thicknesses of the two types of optical information recording media are a and b (a <b), respectively, when information is recorded on or reproduced from the information recording surface of the optical information recording medium having the transparent substrate thickness a. 46. The method according to claim 46, wherein the distance between the negative lens and the positive lens is increased as compared with the case where information is recorded on or reproduced from the information recording surface of the optical information recording medium having the transparent substrate thickness b. The optical pickup device described.   When the transparent substrate thicknesses of the two types of optical information recording media are a and b (a <b), respectively, when information is recorded on or reproduced from the information recording surface of the optical information recording medium having the transparent substrate thickness a. The method further comprises increasing the distance between the negative lens group and the positive lens group as compared to recording or reproducing information on the information recording surface of the optical information recording medium having the transparent substrate thickness b. 47. An optical pickup device according to 47. When the means for correcting the variation of the spherical aberration and the axial chromatic aberration is composed of a positive lens group including the positive lens and a negative lens group including the negative lens, the following expression is satisfied: Item 46. The optical pickup device according to Item 46, 48 or 50.
| FP / fN | ≧ 1.3
However,
fP: focal length of the positive lens group (however, when the positive lens group is provided with a diffractive surface, the total focal length combining the refractive power and the diffractive power)
fN: focal length of the negative lens group (however, when the negative lens group is provided with a diffractive surface, the total focal length combining the refractive power and the diffractive power) 52. The optical pickup device according to claim 47, 49 or 51, wherein:
| FP / fN | ≧ 1.3
However,
fP: focal length of the positive lens group (however, when the positive lens group is provided with a diffractive surface, the total focal length combining the refractive power and the diffractive power)
fN: focal length of the negative lens group (however, when the negative lens group is provided with a diffractive surface, the total focal length combining the refractive power and the diffractive power)   54. The optical pickup device according to claim 36, further comprising a shift device that shifts the movable element along the optical axis in accordance with a change in spherical aberration.   55. The optical pickup device according to claim 36, wherein the movable element is made of a material having a specific gravity of 2.0 or less.   The optical pickup device according to any one of claims 36 to 55, wherein at least one of the positive lens and the negative lens is formed of a plastic material.   56. The optical pickup device according to claim 36, wherein the movable element is made of a plastic material.   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.   58. The optical pickup device according to claim 57, wherein at least one surface of the movable element has an aspheric surface.   The means for correcting the variation of the spherical aberration and the longitudinal chromatic aberration is formed of a material having a saturated water absorption of 0.5% or less. Optical pickup device.   The means for correcting the variation of the spherical aberration and the longitudinal chromatic 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 36 to 60.   The means for correcting the variation of the spherical aberration and the longitudinal chromatic aberration is composed of the one positive lens and the one negative lens. Optical pickup device.   The light according to any one of claims 36 to 62, wherein the means for correcting the variation of the spherical aberration and the longitudinal chromatic aberration includes an optical element having a diffractive surface having an annular diffractive structure. Pickup device.   36. The optical pickup device according to claim 35, wherein the means for correcting the variation of the spherical aberration and the longitudinal chromatic aberration includes an element capable of changing a refractive index distribution.   The optical pickup device according to claim 64, wherein the means for correcting the variation 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. .   66. The optical pickup device according to claim 1, further comprising an optical element having a diffractive surface having an annular diffractive structure.   The optical pickup device according to claim 66, wherein the objective lens is the optical element. 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
However,
fD: The diffractive structure of the objective lens is represented by an optical path difference function defined by Φb = b ₂ h ² + b ₄ h ⁴ + b ₆ h ⁶ +... (where h is a height from the optical axis) a _(mm), b _2, b 4, _{b 6,} ......... 2, fourth, sixth, an optical path difference function coefficients of .........) time, fD = 1 / (- 2 · b ₂ ) The focal length at the oscillation wavelength of the light source defined by only the diffractive structure of the objective lens. F: The objective lens combining the refractive power of the objective lens and the diffractive power of the diffractive structure of the objective lens. Focal length at the oscillation wavelength of the whole light source   The diffractive structure is an n-order diffracted light beam having a diffracted light amount larger than the diffracted light amount of any other order of diffracted light generated by the diffractive structure (where n is other than -1, 0 and +1) In order to record and / or reproduce information on the optical information recording medium, the n-th order diffracted light can be condensed on the information recording surface of the optical information recording medium. 69. The optical pickup device according to claim 33, wherein the optical pickup device is provided.   The optical element having a diffractive surface having a ring-shaped diffractive structure, and the means for correcting the variation of the spherical aberration has an Abbe number of 70.0 or less for all positive lenses including the positive lens, or 34. The optical pickup device according to claim 8, wherein an Abbe number of each of all negative lenses including the negative lens is 40.0 or more.   The means for correcting the variation of the spherical aberration and the axial chromatic aberration has an optical element having a diffractive surface having an annular diffractive structure, and the Abbe number of each of the positive lenses including the positive lens is 70. 64. The optical pickup device according to claim 36, wherein the Abbe number of each of all negative lenses including the negative lens is 40.0 or more. The means for correcting the variation of the spherical aberration is such that the paraxial power at the oscillation wavelength of the light source is P1, the paraxial power at a wavelength 10 nm shorter than the oscillation wavelength is P2, and the paraxial power at a wavelength 10 nm longer than the oscillation wavelength. 71. The optical pickup device according to claim 70, wherein the following expression is satisfied when is set to P3.
P2 <P1 <P3 The means for correcting the variation of the spherical aberration and the longitudinal chromatic aberration is P1 as the paraxial power at the oscillation wavelength of the light source, P2 as the paraxial power at a wavelength 10 nm shorter than the oscillation wavelength, and 10 nm from the oscillation wavelength. 72. The optical pickup device according to claim 71, wherein the following expression is satisfied when a paraxial power at a long wavelength is P3.
P2 <P1 <P3   The diffractive surface has a function of suppressing axial chromatic aberration generated in the objective lens against minute fluctuations in the oscillation wavelength of the light source. The optical pickup device described.   The diffractive surface has a wavelength characteristic such that when the oscillation wavelength of the light source slightly fluctuates toward the long wavelength side, the back focus of the objective lens is shortened. The optical pickup device according to any one of the above.   The diffractive surface has a spherical aberration characteristic that changes in a direction in which the spherical aberration of the objective lens is under-corrected when the oscillation wavelength of the light source slightly fluctuates toward the long wavelength side. 33. An optical pickup device according to any one of 33, 63, 66 to 75. The light source includes at least two light sources, a light source having an oscillation wavelength λ1 and a light source having an oscillation wavelength λ2 (λ1 <λ2),
The condensing optical system transmits the first light beam from the light source having the oscillation wavelength λ1 to the information recording surface of the first optical information recording medium having the transparent substrate thickness t1 for recording or reproducing information. The second light beam that can be condensed with a wavefront aberration of 0.07λ1 rms or less within a predetermined numerical aperture on the image side of the objective lens, and the second light beam emitted from the light source having the oscillation wavelength λ2 has a transparent substrate thickness t2 (t1 ≦ t2). Condensing light with a wavefront aberration of 0.07λ2 rms or less within a predetermined numerical aperture on the image side of the objective lens necessary for recording or reproducing information on the information recording surface of the second optical information recording medium An optical pickup device according to any one of claims 1 to 65.   78. The optical pickup device according to claim 77, comprising an optical element having a diffractive surface having an annular diffractive structure.   The diffractive surface of the optical element records the first light beam emitted from the light source having the oscillation wavelength λ1 on the information recording surface of the first optical information recording medium having the transparent substrate thickness t1, or The second light flux emitted from the light source having the oscillation wavelength λ2 (λ1 <λ2) can be collected within a predetermined numerical aperture on the image side of the objective lens necessary for reproduction with a wavefront aberration of 0.07λ1 rms or less. With respect to the information recording surface of the second optical information recording medium having the transparent substrate thickness t2 (t1 ≦ t2), the wavefront aberration is 0. 0 within a predetermined numerical aperture on the image side of the objective lens necessary for recording or reproducing information. 79. The optical pickup device according to claim 78, wherein the optical pickup device has a wavelength characteristic capable of condensing light in a state of 07λ2 rms or less. A predetermined numerical aperture on the image side of the objective lens necessary for recording or reproducing information by the first light flux emitted from the light source having the oscillation wavelength λ1 with respect to the information recording surface of the first optical information recording medium NA1 and the information recording surface of the second information recording medium on the image side of the objective lens necessary for recording or reproducing information by the second light flux emitted from the light source having the oscillation wavelength λ2. When the predetermined numerical aperture is NA2 (NA1> NA2),
The diffraction surface of the optical element causes the second light beam emitted from the light source having the oscillation wavelength λ2 to have a wavefront aberration of 0.07λ2 rms within the NA1 with respect to the information recording surface of the second optical information recording medium. The optical pickup device according to claim 79, wherein the light is condensed in the above state.   The optical pickup device according to claim 78, wherein the objective lens is the optical element. 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.
0.5 ≦ (f1 / νd) · fD1 ≦ 10.0
However,
f1: Focal length (mm) of the entire objective lens at the oscillation wavelength λ1, which is obtained by combining the refractive power of the objective lens and the diffraction power of the objective lens by the diffraction structure
νd: d-line Abbe number of the objective lens fD1: the diffraction structure of the objective lens is represented by an optical path difference function defined by Φb = b ₂ h ² + b ₄ h ⁴ + b ₆ h ⁶ +. Here, h is a height (mm) from the optical axis, and b ₂ , b ₄ , b ₆ ,... Are second-order, fourth-order, sixth-order,. Where fD = 1 / (− 2 · b ₂ ), focal length (mm) at the oscillation wavelength λ1 due to only the diffractive structure of the objective lens 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
However,
b ₂ : The diffractive structure of the objective lens is represented by an optical path difference function defined by Φb = b ₂ h ² + b ₄ h ⁴ + b ₆ h ⁶ +... (where h is a height from the optical axis) is a _(mm), b _2, b 4, _{b 6,} ......... secondary, fourth, sixth, an optical path difference function coefficients of .........) Part 2 order optical path difference function coefficient when λ1: the oscillation wavelength λ1 (mm)   84. The optical pickup according to claim 78, wherein 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. apparatus.   85. The diffractive surface has a wavelength characteristic such that a back focus of the objective lens is shortened when the oscillation wavelength of the light source slightly fluctuates toward a long wavelength side. The optical pickup device described.   The diffractive surface has a spherical aberration characteristic that changes in a direction in which the spherical aberration of the objective lens is under-corrected when the oscillation wavelength of the light source slightly fluctuates toward the long wavelength side. The optical pickup device according to any one of 78 to 85. The objective lens divides a light beam emitted from the light source into a plurality of light beams by refraction in order from at least one surface toward the outer periphery from the optical axis side, at least a first portion, a second portion, and Having a third part,
The first part and the third part emit light from the light source so that information can be recorded or reproduced on the information recording surface of the first optical information recording medium having a transparent substrate thickness t1. Condensing,
The first portion and the second portion can record or reproduce information on an information recording surface of a second optical information recording medium having a transparent substrate thickness t2 (t1 <t2). 66. The optical pickup device according to claim 1, wherein the light flux from the light source can be condensed. The objective lens divides a light beam emitted from the light source into a plurality of light beams by refraction in order from at least one surface toward the outer periphery from the optical axis side, at least a first portion, a second portion, and Having a third part,
The first part and the third part emit light from the light source having the oscillation wavelength λ1 so that information can be recorded or reproduced on the information recording surface of the first optical information recording medium. Condensing,
The first portion and the second portion emit light beams from the light source having the oscillation wavelength λ2 so that information can be recorded on or reproduced from the information recording surface of the second optical information recording medium. 78. The optical pickup device according to claim 77, wherein the optical pickup device is capable of condensing light. On at least one surface of the objective lens, k incident light fluxes (k ≧ 4) due to refracting action (here, first, second,... In order from the optical axis side toward the outside). ·····, forming a ring-shaped step portion that is divided into k-th luminous flux)
When recording and / or reproducing information on 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 first and k-th light beams is 0.05λ1 rms or less (λ1 light source wavelength),
At least two of the second to (k-1) light beams have an apparent best image plane position at a position different from the best image surface position formed by the first and k-th light beams. ,
Wavefront aberrations of the light beams in the first to k-th light beams that pass through the required numerical aperture for the first optical information recording medium at the best image plane position formed by the first and k-th light beams are almost equal. 78. The optical pickup device according to claim 77, wherein mi [lambda] 1 (mi is an integer, i = 1, 2,..., k).   The transparent substrate thickness t1 of the first optical information recording medium is 0.6 mm or less, the transparent substrate thickness t2 of the second optical information recording medium is 0.6 mm or more, and the oscillation wavelength λ2 is 90. The optical pickup device according to any one of claims 77 to 86, 88, and 89, wherein the optical pickup device has a range of 600 nm to 800 nm. 2. The spherical aberration of the objective lens satisfies the following expression when the third-order spherical aberration component is SA1, and the sum of the fifth-order, seventh-order, and ninth-order spherical aberration components is SA2. The optical pickup device according to any one of Items 1 to 90.
| SA1 / SA2 |> 1.0
However,
SA1: Third-order spherical aberration component when the aberration function is expanded into a Zernike polynomial SA2: Fifth-order spherical aberration component and seventh-order spherical aberration when the aberration function is expanded into a Zernike polynomial Square root of the sum of squares of the component and the ninth-order spherical aberration component   92. The diaphragm 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 vertex of the surface closest to the light source of the objective lens. An optical pickup device according to claim 1.   93. The optical pickup device according to claim 1, wherein the objective lens is a single objective lens having an aspheric surface on at least one surface.   94. The optical pickup device according to claim 1, wherein the light source includes a light source having an oscillation wavelength at a wavelength of at least 500 nm.   95. The optical pickup device according to claim 1, wherein an image-side numerical aperture NA of the objective lens is at least 0.65 or more. The optical pickup device according to claim 1, wherein the objective lens satisfies the following expression.
1.1 ≦ d1 / f ≦ 3.0
However,
d1: On-axis lens thickness (mm)
f: Focal length (mm) at the oscillation wavelength of the light source (however, if the light source has a plurality of light sources having different oscillation wavelengths, the focal length at the oscillation wavelength with the shortest wavelength, and a diffraction surface on the objective lens) If equipped, the total focal length combining the refractive power and diffraction power)   The optical pickup device according to any one of claims 1 to 96, wherein the objective lens is made of a plastic material.   The optical pickup device according to claim 1, wherein the objective lens is formed of a material having a saturated water absorption rate of 0.5% or less.   99. The objective lens according to claim 1, wherein the objective lens 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. Optical pickup device.   An objective lens that is applicable to the optical pickup device according to claim 1.   The objective lens used for the optical pick-up apparatus in any one of Claims 1 thru | or 99 characterized by the above-mentioned. An optical pickup device capable of recording and / or reproducing information with respect to at least two types of optical information recording media, wherein a light source having an oscillation wavelength λ1 and an oscillation wavelength λ2 different from the oscillation wavelength λ1 (λ1 <λ2) And the 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 through the transparent substrate having the transparent substrate thickness t1, and the oscillation is performed. A collecting unit including an objective lens that focuses the second light beam emitted from the light source having the wavelength λ2 on the information recording surface of the second optical information recording medium through the transparent substrate having the transparent substrate thickness t2 (t1 ≦ t2). In an objective lens for an optical pickup device having an optical optical system and a photodetector that receives reflected light from the first and second optical information recording media,
An objective lens characterized by satisfying the following formula.
1.1 ≦ d1 / f ≦ 3.0
However,
d1: On-axis lens thickness (mm)
f: Focal length (mm) at the oscillation wavelength λ1 (however, when the objective lens is provided with a diffractive surface, the total focal length combining the refractive power and the diffractive power)   The objective lens according to claim 102, wherein the image-side numerical aperture NA is 0.75 or more.   The objective lens according to claim 102 or 103, further comprising a diffractive surface having an annular diffractive structure.   The diffractive surface allows the first light beam emitted from the light source having the oscillation wavelength λ1 to be recorded on or reproduced from the information recording surface of the first optical information recording medium. The second light flux emitted from the light source having the oscillation wavelength λ2 can be condensed with a wavefront aberration of 0.07λ1 rms or less within a predetermined numerical aperture on the image side on the information recording surface of the second information recording medium. On the other hand, the optical system has a wavelength characteristic capable of condensing light in a state of wavefront aberration of 0.07λ2 rms or less within a predetermined numerical aperture on the image side of the objective lens necessary for recording or reproducing information. The objective lens described. A predetermined numerical aperture on the image side of the objective lens necessary for recording or reproducing information by the first light flux emitted from the light source having the oscillation wavelength λ1 with respect to the information recording surface of the first optical information recording medium NA1 and the information recording surface of the second information recording medium on the image side of the objective lens necessary for recording or reproducing information by the second light flux emitted from the light source having the oscillation wavelength λ2. When the predetermined numerical aperture is NA2 (NA1> NA2),
The diffraction surface causes the second light beam emitted from the light source having the oscillation wavelength λ2 to have a wavefront aberration of 0.07λ2 rms or more in the NA1 with respect to the information recording surface of the second optical information recording medium. The objective lens according to claim 104 or 105, wherein the objective lens is condensed.   107. The objective lens according to claim 104, wherein the diffractive surface has a function of suppressing axial chromatic aberration with respect to minute fluctuations 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 toward the long wavelength side. Objective lens.   105. The diffractive surface has a spherical aberration characteristic that changes in a direction such that the spherical aberration of the objective lens becomes insufficiently corrected when the oscillation wavelength of the light source slightly fluctuates toward the longer wavelength side. The objective lens in any one of thru | or 108. 110. The objective lens according to claim 102, wherein at least one surface is an aspherical single lens and satisfies the following expression.
0.5 ≦ (f1 / νd) · fD1 ≦ 10.0
However,
f1: Focal length (mm) at the oscillation wavelength λ1 obtained by combining the refractive power and the diffraction power by the diffraction structure
νd: d-line Abbe number of the lens material fD1: the diffraction structure is represented by an optical path difference function defined by Φb = b ₂ h ² + b ₄ h ⁴ + b ₆ h ⁶ +... (where h is FD = 1 when the height from the optical axis (mm) and b ₂ , b ₄ , b ₆ ,... Are second-order, fourth-order, sixth-order,. / (− 2 · b ₂ ), focal length (mm) at the oscillation wavelength λ1 due to the diffraction structure alone 110. The objective lens according to claim 102, wherein at least one surface is an aspherical single lens and satisfies the following expression.
-25.0 ≦ (b ₂ /λ1)≦0.0
However,
b ₂ : The diffraction structure is represented by an optical path difference function defined by Φb = b ₂ h ² + b ₄ h ⁴ + b ₆ h ⁶ +... (where h is a height (mm) from the optical axis) Where b ₂ , b ₄ , b ₆ ,... Are second-order, fourth-order, sixth-order,...)) Second-order optical path difference function coefficients. Wavelength λ1 (mm) 111. Any one of claims 102 to 111, wherein the following equation is satisfied when the third-order spherical aberration component of the spherical aberration is SA1, and the sum of the fifth-order, seventh-order, and ninth-order spherical aberration components is SA2. Objective lens according to the above.
| SA1 / SA2 |> 1.0
However,
SA1: Third-order spherical aberration component when the aberration function is expanded into a Zernike polynomial SA2: Fifth-order spherical aberration component and seventh-order spherical aberration when the aberration function is expanded into a Zernike polynomial Square root of the sum of squares of the component and the ninth-order spherical aberration component At least a first portion, a second portion, and a third portion that divide a light beam emitted from the light source by a refracting action into a plurality of light beams in order from the optical axis side toward the outer periphery on at least one surface. Have
The first part and the third part emit light from the light source having the oscillation wavelength λ1 so that information can be recorded or reproduced on the information recording surface of the first optical information recording medium. Condensing,
The first portion and the second portion emit light beams from the light source having the oscillation wavelength λ2 so that information can be recorded on or reproduced from the information recording surface of the second optical information recording medium. The objective lens according to claim 102, wherein the objective lens is capable of condensing light. At least one surface is provided with k (k ≧ 4) ring-shaped light beams by refraction (here, first, second,... In order from the optical axis side toward the outside). , The k-th luminous flux) to be divided into annular zones,
When recording and / or reproducing information on 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 first and k-th light beams is 0.05λ1 rms or less (λ1 light source wavelength),
At least two of the second to (k-1) light beams have an apparent best image plane position at a position different from the best image surface position formed by the first and k-th light beams. ,
Wavefront aberrations of the light beams in the first to k-th light beams that pass through the required numerical aperture for the first optical information recording medium at the best image plane position formed by the first and k-th light beams are almost equal. 104. The objective lens according to claim 102 or 103, wherein mi [lambda] 1 (mi is an integer, i = 1, 2,..., k).   115. The objective lens according to claim 102, wherein the objective lens is made of a plastic material.   The objective lens according to any one of claims 102 to 115, wherein the objective lens is formed of a material having a saturated water absorption rate of 0.5% or less.   The objective lens according to any one of claims 102 to 116, wherein the objective lens is made of a material having an internal transmittance of 85% or more at a thickness of 3 mm with respect to an oscillation wavelength of the light source.   118. The objective lens according to claim 102, wherein at least one surface is an aspherical single lens. 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.   And including at least one positive lens and at least one negative lens, at least one of which is a movable element that can be displaced along the optical axis direction. Each Abbe number of all positive lenses including the positive lens 70.0 or less, or the Abbe number of each of all negative lenses including the negative lens is 40.0 or more, and at least one surface has a diffractive surface having an annular diffractive structure. . When the paraxial power at the oscillation wavelength of the light source that outputs 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 a wavelength 10 nm longer than the oscillation wavelength is P3, 121. The beam expander according to claim 120, wherein the following formula is satisfied.
P2 <P1 <P3   The diffractive surface has a function of suppressing axial chromatic aberration generated in a condensing lens arranged on the exit side with respect to minute fluctuations in an oscillation wavelength of a light source that outputs an incident light beam. 120. The beam expander according to 120 or 121.   The diffractive surface has a wavelength characteristic such that when the oscillation wavelength of the light source that outputs the incident light beam slightly fluctuates to the long wavelength side, the back focus of the condenser lens arranged on the output side is shortened. The beam expander according to any one of claims 120 to 122.   The diffractive surface is a spherical surface that changes in such a direction that the spherical aberration of the condensing lens arranged on the output side is under-corrected when the oscillation wavelength of the light source that outputs the incident light beam slightly fluctuates to the long wavelength side. 124. The beam expander according to any one of claims 120 to 123, wherein the beam expander has aberration characteristics.   The beam expander according to any one of claims 120 to 124, wherein the movable element is made of a material having a specific gravity of 2.0 or less.   126. The beam expander according to any one of claims 120 to 125, wherein the movable element is made of a plastic material.   127. The beam expander according to any one of claims 120 to 126, wherein at least one surface of the movable element has an aspheric surface.   128. The beam expander according to any one of claims 120 to 127, wherein the movable element is made of a material having a saturated water absorption rate of 0.5% or less.   131. The movable element according to any one of claims 120 to 128, 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 an incident light source. The described beam expander.   The beam expander according to any one of claims 120 to 124, wherein the beam expander is made of a plastic material.   131. The beam expander according to any one of claims 120 to 124, 130, wherein the beam expander has at least one aspheric surface.   132. The beam expander according to any one of claims 120 to 124, 130, and 131, which is made of a material having a saturated water absorption rate of 0.5% or less.   The light source 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 an incident light source. Beam expander.   The beam expander according to any one of claims 120 to 133, wherein the beam expander is applicable to the optical pickup device according to any one of claims 8 to 33 and 36 to 63.