JP2003066326A - Optical element used for optical pickup device, optical pickup device, and optical information recording/ reproducing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical element which is arranged near a plastic objective lens for a short wavelength having a high NA and limited magnification and corrects the deterioration of a wavefront aberration (spherical aberration) occurring as total also during a temperature change accompanying the wavelength change of a light source, to provide especially an optical element in which a diffraction structure is formed at least at one side, and to provide an optical pickup device having the optical element, and an optical information recording medium player. SOLUTION: The diffraction structure formed in the optical element corrects the deterioration of the aberration caused by the temperature change even when the plastic objective lens comprises an aspheric refraction plane. In the case that the optical element is made into a parallel flat plate (OE), a surface on which a diffraction orbicular zone R is formed becomes a plane orthogonal to an optical axis, which reduces the number of vignetting in luminous flux, and increases the light quantity of the luminous flux condensed by the optical information recording medium compared to the case that the diffraction structure is formed in the objective lens.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical element, an optical pickup device and an optical information recording / reproducing apparatus, and more particularly to an optical element for suppressing deterioration of spherical aberration, and an optical pickup device including such an optical element. The present invention relates to an optical information recording / reproducing device.

[0002]

2. Description of the Related Art In an optical information recording / reproducing apparatus for recording / reproducing information by using a laser beam or the like, in order to increase its capacity, the wavelength of a light source is shortened and the numerical aperture of an objective lens (N
A) Up is being considered. This optical information recording / reproducing apparatus has an optical pickup device for recording / recording an optical information recording medium.
At the time of reproduction, the light flux from the laser light source is focused on the information recording surface of the optical information recording medium by using the objective lens, and thereby reading and writing of information is performed. In this objective lens, a plastic objective lens is widely used because of its stable production performance.

However, in general, the change in refractive index due to temperature change in plastic is larger than that of glass by one digit or more, so that there is concern that the performance may deteriorate when the temperature changes. Although the optical pickup device has a focusing function for the objective lens, it has a high NA required for high-density optical information recording, a short wavelength, and an optical system required for downsizing the device. Due to the finite magnification, the performance deterioration tends to become more prominent, and some measure to prevent the wavefront aberration deterioration is required.

By the way, it is known that the objective lens is provided with a ring-shaped diffractive structure to suppress the deterioration of the wavefront aberration when the temperature changes. Normally, when the temperature of the optical pickup device changes, the wavelength of the light source also changes. By utilizing the fact that the power of the diffractive part is proportional to the wavelength, the spherical aberration in the under direction is generated in the diffractive part, in contrast to the over spherical aberration that results from the decrease in the refractive index due to the plastic characteristics in the refractive part with the rise in temperature. It can be canceled by doing so.
By properly balancing the powers of the refracting portion and the diffracting portion, it is possible to suppress deterioration of the wavefront aberration (in this case, spherical aberration) when the temperature changes.

However, when a diffractive structure is provided on the objective lens, the diffractive structure is formed on the base spherical surface (or the base aspherical surface) which is the lens surface. Vignetting will occur. This will be described with reference to the drawings.

FIG. 1 is a diagram showing a part of a sectional view of an objective lens provided with a diffractive structure. In FIG. 1, a diffractive structure including a sawtooth ring R is formed on a mother aspheric surface S of the objective lens. Here, when considering a light beam entering one ring zone, the light beam LB1 entering the root side of the sawtooth is refracted at an angle designed by passing through the diffractive ring zone,
The light beam LB2 incident on the tip side of the sawtooth is incident on the diffractive ring zone and then reflected outward by the inner side surface thereof, which is a problem of so-called ray shading. Therefore, the light beam LB2 becomes ineffective light that cannot be used for information recording / reproduction, and it is necessary to increase the irradiation light intensity of the light source accordingly. The vignetting of this light ray tends to increase when the NA is high or when the light ray is incident at a finite angle.

In order to eliminate the temperature (suppress the deterioration of the aberration due to the temperature change) by providing a diffractive structure in the objective lens whose specifications have severe temperature characteristics, it is generally necessary to increase the diffraction power. As a result, the diffraction pitch is reduced. However, since the pitch of the diffraction pitch is usually narrower toward the periphery, there is a concern that the diffraction efficiency of the periphery may be significantly reduced due to the pitch phenomenon. As described above, a problem also occurs when the temperature is erased by forming the diffraction structure on the objective lens.

The present invention has been made in view of the above-mentioned problems, and is arranged close to a plastic objective lens having a high NA, a finite magnification, and a short wavelength, and even when the temperature of the light source changes due to wavelength fluctuation, To provide an optical element for correcting deterioration of wavefront aberration (spherical aberration) generated as a whole, particularly an optical element having a diffractive structure formed on at least one surface thereof, an optical pickup device having the optical element, and an optical information recording medium reproducing device. To aim.

[0009]

An optical element according to claim 1 is provided with a light source having a wavelength λ, an objective lens for focusing a light beam from the light source on an optical information recording medium, and an optical element. In an optical element used in an optical pickup device having an optical system and a photodetector for sensing reflected light of an image formation spot on an optical information recording medium, the objective lens of the optical system has a positive refractive power. A plastic objective lens having the optical element and the optical element when the light flux from the light source forms an image on an optical information recording medium and when the reflected light from the optical information recording medium enters a photodetector. A plastic objective lens is present in the optical path, and at least one surface of the optical element has a ring-shaped diffractive structure formed in the effective light beam passage area, and the optical element alone has a paraxial positive refractive power. , Some Has no refracting power and has a characteristic of generating under spherical aberration when a light beam with a longer wavelength is incident than when a light beam with a predetermined wavelength is incident, so that the plastic objective lens Even when it is composed of an aspherical refracting surface, it is possible to correct the deterioration of aberration due to temperature change by the diffractive structure formed in the optical element. Further, as shown in FIG. 2, if the optical element is a parallel plate (OE), the surface forming the diffractive ring zone R is a plane orthogonal to the optical axis, so that the diffractive structure is formed on the objective lens. Compared with the case, it is possible to reduce the amount of vignetting in the incident light beam and increase the light amount of the light beam condensed on the optical information recording medium. That is, considering the diffraction efficiency of the diffraction structure, by providing the diffraction structure of the optical element so as to be a substantially flat surface, it is possible to improve the diffraction efficiency and reduce the light ray vignetting at the end of the diffractive ring zone. .

When the optical element according to claim 2 is arranged adjacent to the plastic objective lens, the optical element can be easily positioned in the direction perpendicular to the optical axis by being fitted with the objective lens, for example. When a diaphragm function, which will be described later, is given to the optical element, that function is easily exhibited.

According to a third aspect of the present invention, the sum φD of paraxial powers of the diffractive structure formed on the optical element is:
When the combined focal length of the objective lens and the optical element is f, −0.1 <φD · f <0.0 (1). That is, it is possible to give the optical element paraxial power, in which case it is possible to weaken the positive paraxial power of the objective lens, thereby improving the temperature characteristic of the objective lens. Become. At this time, the paraxial power of the diffractive structure of the optical element
By setting it to 0.1 or more and 0.0 or less, it is possible to improve the temperature characteristics of the optical system and widen the ring zone pitch of the diffractive structure. According to this structure, the lens has a two-lens structure while having the same temperature characteristics as in the case where the objective lens is provided with a diffractive structure, but it is possible to increase the total light transmittance.

In the optical element according to the fourth aspect, when the utilized diffraction order is represented by n, the minimum value pmin of the diffraction pitch within the effective diameter.
Is 5λ <pmin / n <20λ (2), it is suppressed that the pitch becomes too small and the transmittance decreases, and that the pitch becomes too large and the diffracted light rate decreases.

In the optical element according to the fifth aspect, as shown in FIG.
As shown in FIG. 4, the flat surface f outside the effective diameter has a diaphragm function of limiting the diameter of the light beam incident on the objective lens. Therefore, it is not necessary to provide a separate diaphragm, and the cost of the optical pickup device can be reduced. Contribute. The surface f may be coated with a light blocking effect.

In the optical element according to the sixth aspect, since the objective lens is composed of aspherical refracting surfaces on both sides,
Even with one objective lens, better optical characteristics can be obtained.

In the optical element according to claim 7, the optical system including the objective lens and the optical element has a combined focal length f, a numerical aperture NA on the optical information recording medium side, and an imaging magnification m.
Respectively satisfy 2.0 mm <f <5.0 mm (3) 0.48 <NA <0.65 (4) −1/3 <m ≦ 0 (5). If the combined focal length f exceeds the lower limit of the expression (3), the temperature characteristic of the objective lens deteriorates, so the effect of using the optical element of the present invention is effectively exhibited, and if the combined focal length f falls below the lower limit, It can be used in an existing optical pickup device. Numerical aperture NA
Is in the range of the formula (4) and the imaging magnification m is in the range of the formula (5), it can be suitably used for recording or reproducing optical information such as CD and DVD.

In the optical element according to claim 8, the optical system including the objective lens and the optical element has a combined focal length f, a numerical aperture NA on the optical information recording medium side, and an imaging magnification m.
Respectively satisfy 0.3 mm <f <1.0 mm (6) 0.75 <NA <0.90 (7) −1/3 <m ≦ 0 (8). By satisfying the above expression, it is possible to perform excellent optical information recording or reproduction by using a light flux from a light source of a short wavelength such as a so-called blue laser.

When the optical element according to the ninth aspect is made of a plastic material, the diffractive structure can be formed easily with high precision by, for example, molding.

If the optical element according to claim 10 and the objective lens are integrated by fitting, the optical axis can be accurately positioned. As a mode of fitting, as shown in FIG. 4, it is conceivable that the outer circumference of the optical element OE is extended in the optical axis direction and fitting is performed on the flange surface of the objective lens OL.

According to the eleventh aspect of the present invention, there is provided a transparent substrate thickness t1 and a first light source having a wavelength λ1 used for recording / reproduction of a first optical information recording medium and a transparent substrate thickness t2 (t.
2> t1), the second light source of wavelength λ2 (λ2> λ1) used at the time of recording / reproducing of the second optical information recording medium, and the light fluxes from the first and second light sources, Optical system including an objective lens and an optical element for forming an image on the second optical information recording medium, and light for sensing reflected light of the image forming spots on the first and second optical information recording media In an optical element used in an optical pickup device having a detector, the objective lens of the optical system is a plastic objective lens having a positive refracting power, and the plastic objective lens and the optical element have a first optical information. The photodetector is used when the recording medium is used and when the second optical information recording medium is used, and when the luminous flux from each light source forms an image on each optical information recording medium and the reflected light from each optical information recording medium is used. When incident on Also in this case, the optical element and the plastic objective lens are present in the optical path, and the optical element has a ring-shaped diffractive structure formed on at least one surface in the effective light beam passage region, and the optical element alone has a paraxial positive axis. It does not have a refractive power or a refractive power of, and has a characteristic of generating an under spherical aberration when a light beam of a longer wavelength side is incident than when a light beam of a predetermined wavelength is incident. Characterize.

That is, the transparent substrate has a different thickness (t2>
t1) In a so-called compatible optical pickup device that records or reproduces information on or from an optical information recording medium, if the wavelength used in each optical information recording medium is different and λ2> λ1, this optical element is It can be effectively applied. In such a compatible optical pickup device, in general,
This is because restrictions such as temperature characteristics of the objective lens are very severe. According to the present invention, even if a plastic objective lens is used, temperature correction can be performed while correcting spherical aberration in each transparent substrate thickness as a total optical element. For example, when achieving compatibility between a DVD (first optical information recording medium example) using λ1 = 650 to 660 nm and a CD (second optical information recording medium example) using λ2 = 780 to 790 nm Is the magnification m1 when the first optical information recording medium is used.
When the second optical information recording medium is used and the magnification m2 is substantially the same, it becomes easier to achieve both spherical aberration correction and temperature characteristic improvement.

An optical element according to a twelfth aspect is arranged adjacent to the plastic objective lens. The effect of the present invention is the same as that of the invention described in claim 2.

According to a thirteenth aspect of the present invention, there is provided the optical element according to the first aspect.
The required numerical aperture NA1 of the objective lens when the optical information recording medium is used and the required numerical aperture NA2 of the objective lens when the second optical information recording medium is used are NA1> NA.
2, the optical element has different diffractive structure designs in at least two regions, and light rays that define the required numerical aperture NA2 when the second optical information recording medium is used intersect at any boundary position. It is characterized by being almost the same as the position. This condition is necessary to record information on different optical information recording media using the same optical pickup device. It should be noted that "diffraction structure design is different in at least two regions" means, for example, when recording or reproducing information on the first optical information recording medium, convergent light is emitted and the second optical information recording medium is emitted. When recording or reproducing information on or from an optical information recording medium, it refers to designing a diffractive structure so as to emit flare light, but is not limited thereto.

The optical element according to claim 14 has a wavelength of λ1.
The sum φD1 of the powers of the diffractive structures formed in the optical element at −0.1 <φD1 · f1 <0.0, where f1 is the combined focal length of the objective lens and the optical element. ) Is. The effect of the present invention is the same as that of the invention described in claim 3.

In the optical element according to the fifteenth aspect, when the utilized diffraction order is n, the minimum value pm of the diffraction pitch within the effective diameter is given.
in is characterized by 5λ <pmin / n <20λ (10). The effect of the present invention is the same as that of the invention described in claim 4.

An optical element set forth in (16) is characterized in that it has a diaphragm function for limiting a light beam having a required numerical aperture NA1 which enters the objective lens. The effect of the present invention is
This is the same as the invention described in claim 5.

The optical element according to the seventeenth aspect is characterized in that the objective lens is composed of aspherical refracting surfaces on both sides. The operation and effect of the present invention is the same as that of the invention described in claim 6.

In the optical element according to claim 18, the optical system including the objective lens and the optical element has a combined focal length f1 at a wavelength λ1, a numerical aperture NA1 on the optical information recording medium side, and an imaging magnification. Each of m1 is characterized by satisfying 2.0 mm <f1 <5.0 mm (11) 0.48 <NA1 <0.65 (12) −1/3 <m1 ≦ 0 (13). The operation and effect of the present invention is the same as that of the invention described in claim 7.

In the optical element according to claim 19, in the optical system including the objective lens and the optical element, the imaging magnifications m1 and m2 at wavelengths λ1 and λ2 are m2 = m1 = 0 or 0. Since 9 <m1 / m2 <1.1 (14) is satisfied, information can be satisfactorily recorded or reproduced on or from each optical information recording medium.

An optical element set forth in (20) is characterized in that it is made of a plastic material. The operation and effect of the present invention is the same as that of the invention described in claim 8.

An optical element according to a twenty-first aspect and the objective lens are integrated by fitting. The operation and effect of the present invention is the same as that of the invention described in claim 9.

An optical pickup device according to a twenty-second aspect of the invention is an optical system including a light source of wavelength λ, an objective lens for focusing a light beam from the light source on an optical information recording medium, and an optical element, and an optical system. In an optical pickup device having a photodetector for sensing reflected light of an image formation spot on an information recording medium, the objective lens of the optical system is a plastic objective lens having a positive refractive power, The optical element and the plastic objective lens exist in the optical path both when the light flux of is imaged on the optical information recording medium and when the reflected light from the optical information recording medium enters the photodetector. In the optical element, a ring-shaped diffractive structure is formed on at least one surface in the effective light flux passage area, and the optical element alone has paraxially positive refracting power or does not have refracting power. Compared with the case where the light beam of a predetermined wavelength is incident, and having the property of generating a spherical aberration of the under if from the light flux of the long wavelength side it enters. The effect of the present invention is the same as that of the invention described in claim 1.

The optical pickup apparatus described in Item 23 is characterized in that the optical element is arranged adjacent to the plastic objective lens. The effect of the present invention is the same as that of the invention described in claim 2.

In the optical pickup device according to the twenty-fourth aspect, when the sum φD of paraxial powers of the diffractive structure formed on the optical element is a combined focal length of the objective lens and the optical element, f. In addition, −0.1 <φD · f <0.0 (15). The effect of the present invention is the same as that of the invention described in claim 3.

In the optical pickup device of the twenty-fifth aspect, in the optical element, the minimum value pmin of the diffraction pitch within the effective diameter is 5λ <pmin / n <20λ (16) when the utilized diffraction order is represented by n. It is characterized by The effect of the present invention is the same as that of the invention described in claim 4.

The optical pickup apparatus described in Item 26 is characterized in that the optical element has a diaphragm function for limiting the diameter of a light beam incident on the objective lens. The operation and effect of the present invention is the same as that of the invention described in claim 5.

In the optical pickup device according to the twenty-seventh aspect, the objective lens is composed of aspherical refracting surfaces on both sides. The operation and effect of the present invention is the same as that of the invention described in claim 6.

In the optical pickup device according to the twenty-eighth aspect, the optical system including the objective lens and the optical element has a combined focal length f and a numerical aperture N on the optical information recording medium side.
A, the imaging magnification m satisfies 2.0 mm <f <5.0 mm (17) 0.48 <NA <0.65 (18) −1/3 <m ≦ 0 (19), respectively. To do. The operation and effect of the present invention is the same as that of the invention described in claim 7.

According to a twenty-ninth aspect of the invention, in the optical pickup device, the optical system including the objective lens and the optical element has a combined focal length f and a numerical aperture N on the optical information recording medium side.
A, the imaging magnification m satisfies 0.3 mm <f <1.0 mm (20) 0.75 <NA <0.90 (21) −1/3 <m ≦ 0 (22), respectively. The function and effect of the present invention are the same as those of the invention according to claim 8.

The optical pickup apparatus described in Item 30 is characterized in that the optical element is made of a plastic material. The operation and effect of the present invention is the same as that of the invention described in claim 9.

The optical pickup device described in (31) is characterized in that the optical element and the objective lens are integrated by fitting. The operation and effect of the present invention is the same as that of the invention of claim 10.

According to a thirty-second aspect of the present invention, in the optical pickup device described above, the first light source of the wavelength λ1 used at the time of recording / reproducing of the first optical information recording medium having the transparent substrate thickness t1, and the transparent substrate thickness t2 (t2 > T1) and the second wavelength λ2 (λ2> λ1) used when recording / reproducing on the second optical information recording medium.
The light source and the light fluxes from the first and second light sources
And an optical system including an objective lens and an optical element for forming an image on the second optical information recording medium, and for sensing reflected light of image forming spots on the first and second optical information recording media. In the optical pickup device including the photodetector, the objective lens of the optical system is a plastic objective lens having a positive refractive power, and the plastic objective lens and the optical element are the first optical information recording medium use. And when the second optical information recording medium is used, and when the light flux from each of the light sources forms an image on each optical information recording medium,
In any case when the reflected light from each optical information recording medium is incident on the photodetector, the optical element and the plastic objective lens are present in the optical path, and the optical element has a ring-shaped diffraction pattern on at least one surface. The structure is formed in the effective light flux passage area, and the optical element itself does not have a positive refractive power or refractive power paraxially, and it has a longer wavelength side than that when a light flux of a predetermined wavelength is incident. Is characterized by having a property of generating an under spherical aberration when the light flux of is incident. The operation and effect of the present invention is the same as that of the invention of claim 11.

The optical pickup device described in Item 33 is characterized in that the optical element is disposed adjacent to the plastic objective lens. The effect of the present invention is the same as that of the invention described in claim 2.

In the optical pickup device according to the thirty-fourth aspect, the required numerical aperture NA1 of the objective lens when using the first optical information recording medium and the need of the objective lens when using the second optical information recording medium. Numerical aperture NA2 is
A light ray having a relation of NA1> NA2, the optical element having different diffractive structure design in at least two regions, and one of the boundary positions thereof defines a required numerical aperture NA2 when the second optical information recording medium is used. It is characterized in that it is almost the same as the position where The operation and effect of the present invention is the same as that of the invention described in claim 13.

In the optical pickup device according to the thirty-fifth aspect, the sum φD1 of the powers of the diffractive structures formed on the optical element at the wavelength λ1 is the combined focal length of the objective lens and the optical element as f1. In this case, −0.1 <φD1 · f1 <0.0 (23). The effect of the present invention is the same as that of the invention described in claim 3.

In the optical pickup device according to the thirty-sixth aspect, when the utilized diffraction order of the optical element is n, the minimum value pmin of the diffraction pitch within the effective diameter is 5λ <pmin / n <20λ (24). It is characterized by being. The effect of the present invention is the same as that of the invention described in claim 4.

In the optical pickup device according to the thirty-seventh aspect of the invention, the optical element has a diaphragm function for limiting a light beam having a required numerical aperture NA1 incident on the objective lens. The operation and effect of the present invention is the same as that of the invention described in claim 5.

The optical pickup apparatus described in Item 38 is characterized in that the objective lens is constructed by a refracting surface having aspherical surfaces on both sides. The operation and effect of the present invention is the same as that of the invention described in claim 6.

In the optical pickup device according to a thirty-ninth aspect, in the optical system including the objective lens and the optical element, a combined focal length f1 at a wavelength λ1, a numerical aperture NA1 on the optical information recording medium side, an image formation The magnification m1 is characterized by satisfying 2.0 mm <f1 <5.0 mm (25) 0.48 <NA1 <0.65 (26) −1/3 <m1 ≦ 0 (27), respectively. The operation and effect of the present invention is the same as that of the invention described in claim 7.

In the optical pickup device according to claim 40, the optical system in which the objective lens and the optical element are combined has imaging magnifications m1 and m2 at wavelengths λ1 and λ2.
However, m2 = m1 = 0 or 0.9 <m1 / m2 <1.1 (28) is satisfied. The operation and effect of the present invention is the same as that of the invention of claim 14.

The optical pickup device described in Item 41 is characterized in that the optical element is made of a plastic material. The operation and effect of the present invention is the same as that of the invention described in claim 9.

The optical pickup device described in Item 42 is characterized in that the optical element and the objective lens are integrated by fitting. The operation and effect of the present invention is the same as that of the invention of claim 10.

In the optical pickup device according to the forty-third aspect, since the first light source and the second light source are composed of a single unit, a light source such as a so-called two-laser-one package can be used. The overall size of the device can be reduced.

The optical pickup device according to a forty-fourth aspect is from the first light source to the surface of the first optical information recording medium when recording or reproducing information on the first optical information recording medium. Is almost equal to the distance from the second light source to the surface of the second optical information recording medium when information is recorded or reproduced on the second optical information recording medium, so that the so-called compatibility formula The optical pickup device can be made more compact.

An optical information recording / reproducing apparatus according to a forty-fifth aspect of the present invention is an optical system including a light source of wavelength λ, an objective lens for focusing a light beam from the light source on an optical information recording medium, and an optical element. In an optical information recording / reproducing apparatus including an optical pickup device having a photodetector for sensing reflected light of an image formation spot on the optical information recording medium, the objective lens of the optical system has a positive refractive power. It is a plastic objective lens, and when the light flux from the light source forms an image on the optical information recording medium and when the reflected light from the optical information recording medium enters the photodetector, the optical element and the plastic The objective lens is present in the optical path, the optical element has a ring-shaped diffractive structure formed on at least one surface in the effective light beam passage region, and the optical element alone has a paraxial positive refractive power, Some Has no refracting power, and has a characteristic of generating an under spherical aberration when a light beam having a longer wavelength is incident than when a light beam having a predetermined wavelength is incident. . The effect of the present invention is
This is similar to the invention described in claim 1.

An optical information recording / reproducing apparatus according to a 46th aspect of the invention is characterized in that the optical element is arranged adjacent to the plastic objective lens. The effect of the present invention is the same as that of the invention described in claim 2.

In the optical information recording / reproducing apparatus according to the forty-seventh aspect, the sum φD of paraxial powers of the diffractive structure formed on the optical element is f, and the combined focal length of the objective lens and the optical element is f. In this case, -0.1 <φD · f <0.0 (29). The effect of the present invention is the same as that of the invention described in claim 3.

In the optical information recording / reproducing apparatus according to the forty-eighth aspect, in the optical element, the minimum value pmin of the diffraction pitch within the effective diameter is 5λ <pmin / n <20λ (30) when the utilized diffraction order is represented by n. Is characterized in that. The effect of the present invention is the same as that of the invention described in claim 4.

An optical information recording / reproducing apparatus according to a forty-ninth aspect is characterized in that the optical element has a diaphragm function of limiting a diameter of a light beam incident on the objective lens. The operation and effect of the present invention is the same as that of the invention described in claim 5.

An optical information recording / reproducing apparatus according to a 50th aspect of the invention is characterized in that the objective lens is composed of a refracting surface having aspherical surfaces on both sides. The operation and effect of the present invention is the same as that of the invention described in claim 6.

In the optical information recording / reproducing apparatus according to a fifty-first aspect, the optical system including the objective lens and the optical element has a combined focal length f and a numerical aperture N on the optical information recording medium side.
A, the imaging magnification m satisfies 2.0 mm <f <5.0 mm (31) 0.48 <NA <0.65 (32) −1/3 <m ≦ 0 (33), respectively. To do. The operation and effect of the present invention is the same as that of the invention described in claim 7.

In the optical pickup apparatus described in Item 52, the optical system including the objective lens and the optical element has a combined focal length f and a numerical aperture N on the optical information recording medium side.
A, the imaging magnification m satisfies 0.3 mm <f <1.0 mm (34) 0.75 <NA <0.90 (35) −1/3 <m ≦ 0 (36), respectively. The function and effect of the present invention are the same as those of the invention according to claim 8.

The optical information recording / reproducing apparatus described in (53) is characterized in that the optical element is made of a plastic material. The operation and effect of the present invention is the same as that of the invention described in claim 9.

The optical information recording / reproducing apparatus described in (54) is characterized in that the optical element and the objective lens are integrated by fitting. The operation and effect of the present invention is the same as that of the invention of claim 10.

According to a 55th aspect of the present invention, in an optical information recording / reproducing apparatus, a transparent substrate thickness t2 and a first light source having a wavelength λ1 used for recording / reproducing of a first optical information recording medium having a transparent substrate thickness t1. The second wavelength λ2 (λ2> λ1) used for recording / reproducing of the second optical information recording medium with (t2> t1).
The light source and the light fluxes from the first and second light sources
And an optical system including an objective lens and an optical element for forming an image on the second optical information recording medium, and for sensing reflected light of image forming spots on the first and second optical information recording media. In the optical information recording / reproducing apparatus including an optical pickup device having a photodetector, the objective lens of the optical system is a plastic objective lens having a positive refractive power, and the plastic objective lens and the optical element are When the first optical information recording medium is used and when the second optical information recording medium is used, the luminous flux from each light source forms an image on each optical information recording medium, and the reflected light from each optical information recording medium In any case when the light enters the photodetector, the optical element and the plastic objective lens are present in the optical path, and the optical element has a ring-shaped diffractive structure on at least one surface of the effective light beam passage region. Are formed on, does not have a positive refractive power or refractive power in a paraxial manner as an optical element alone,
Compared with the case where a light beam having a predetermined wavelength is incident, it has a characteristic of generating under spherical aberration when a light beam having a longer wavelength is incident. The operation and effect of the present invention is the same as that of the invention of claim 11.

The optical information recording / reproducing apparatus described in Item 56 is characterized in that the optical element is arranged adjacent to the plastic objective lens. The effect of the present invention is the same as that of the invention described in claim 2.

According to a 57th aspect of the present invention, there is provided an optical information recording / reproducing apparatus in which the required numerical aperture NA1 of the objective lens when the first optical information recording medium is used and the objective lens when the second optical information recording medium is used. The required numerical aperture NA2 of
A light ray having a relation of NA1> NA2, the optical element having different diffractive structure design in at least two regions, and one of the boundary positions thereof defines a required numerical aperture NA2 when the second optical information recording medium is used. It is characterized in that it is almost the same as the position where The operation and effect of the present invention is the same as that of the invention of claim 12.

In the optical information recording / reproducing apparatus according to the 58th aspect of the invention, the sum φD1 of the powers of the diffractive structures formed on the optical element at the wavelength λ1 is the combined focal length of the objective lens and the optical element by f1. In this case, -0.1 <φD1 · f1 <0.0 (37). The effect of the present invention is the same as that of the invention described in claim 3.

According to a 59th aspect of the present invention, in the optical information recording / reproducing apparatus, the minimum value pmin of the diffraction pitch within the effective diameter of the optical element is 5λ <pmin / n <20λ (38), where the utilized diffraction order is n. ) Is. The effect of the present invention is the same as that of the invention described in claim 4.

According to the 60th aspect of the present invention, there is provided an optical information recording / reproducing apparatus in which the optical element has a diaphragm function of limiting a light beam having a required numerical aperture NA1 incident on an objective lens. The operation and effect of the present invention is the same as that of the invention described in claim 5.

An optical information recording / reproducing apparatus according to a sixty-first aspect is characterized in that the objective lens is composed of a refracting surface having aspherical surfaces on both sides. The operation and effect of the present invention is the same as that of the invention described in claim 6.

In the optical information recording / reproducing apparatus according to a sixty-second aspect, the optical system including the objective lens and the optical element has a combined focal length f1 at a wavelength λ1, a numerical aperture NA1 on the optical information recording medium side, The imaging magnification m1 is characterized by satisfying respectively 2.0 mm <f1 <5.0 mm (39) 0.48 <NA1 <0.65 (40) −1/3 <m1 ≦ 0 (41). . The operation and effect of the present invention is the same as that of the invention described in claim 7.

In the optical information recording / reproducing apparatus according to a sixty-third aspect, the optical system including the objective lens and the optical element has imaging magnifications m1 and m2 at wavelengths λ1 and λ2.
However, m2 = m1 = 0 or 0.9 <m1 / m2 <1.1 (42) is satisfied. The operation and effect of the present invention is the same as that of the invention described in claim 19.

An optical information recording / reproducing apparatus according to a sixty-fourth aspect is characterized in that the optical element is made of a plastic material. The operation and effect of the present invention is the same as that of the invention described in claim 9.

The optical information recording / reproducing apparatus according to a sixty-fifth aspect is characterized in that the optical element and the objective lens are integrated by fitting. The operation and effect of the present invention is the same as that of the invention of claim 10.

An optical information recording / reproducing apparatus according to a sixty-sixth aspect is characterized in that the first light source and the second light source are composed of a single unit. The operation and effect of the present invention is the same as that of the invention of claim 43.

According to a 67th aspect of the present invention, there is provided an optical information recording / reproducing apparatus in which the first optical information recording medium is read from the first light source when recording or reproducing information on the first optical information recording medium. The distance to the surface is substantially equal to the distance from the second light source to the surface of the second optical information recording medium when recording or reproducing information on the second optical information recording medium. And The operation and effect of the present invention is the same as that of the invention of claim 44.

The diffractive structure used in the present specification refers to a structure in which a relief is provided on the surface of an optical element so as to have a function of condensing or diverging a light beam by diffraction. As the relief shape, for example, on the surface of the optical element, it is formed as a substantially concentric annular zone centered on the optical axis, and when viewed in a plane including the optical axis, each annular zone has a sawtooth-like shape. Are known, but include such shapes.

In the present specification, the objective lens is, in a narrow sense, a collection arranged to face the optical information recording medium at a position closest to the optical information recording medium when the optical information recording medium is loaded in the optical pickup device. Refers to a lens that has a light effect,
In a broad sense, the term refers to a lens group that can be actuated at least in the optical axis direction by a focusing mechanism together with the lens. Here, such a lens group refers to at least one lens (for example, two lenses). Therefore, in the present specification, the numerical aperture NA of the objective lens on the optical information recording medium side (image side) refers to the numerical aperture NA of the lens surface of the objective lens located closest to the optical information recording medium side. . Further, in the present specification, the required numerical aperture NA is a numerical aperture defined by the standard of each optical information recording medium or information of each optical information recording medium according to the wavelength of a light source used. The numerical aperture of the diffraction-limited performance objective lens capable of obtaining the spot diameter required for recording or reproduction is shown.

In the present specification, the second optical information recording medium means, for example, various CD type optical disks such as CD-R, CD-RW, CD-Video, and CD-ROM, and the first optical information recording medium. The information recording medium means various DVD-based optical discs such as DVD-ROM, DVD-RAM, DVD-R, DVD-RW, and DVD-Video.

[0080]

DETAILED DESCRIPTION OF THE INVENTION The present invention will be described in more detail with reference to the drawings.

(First Embodiment) A first embodiment will be described. FIG. 5 is a schematic configuration diagram of an optical pickup device including an optical element according to the present embodiment (an optical information recording / reproducing device incorporating the same is not shown). In FIG. 4, a light beam from a semiconductor laser 1 as a light source passes through a beam splitter 2 and is incident on an objective lens 4 adjacent to it through an optical element 3 which is a parallel plate having a diffractive structure as shown in FIG. Then, the light is focused on the information recording surface of the optical information recording medium 5. On the other hand, the light reflected from the optical information recording medium 5 passes through the objective lens 4 and the optical element 3, is reflected by the beam splitter 2 in a direction different from that of the semiconductor laser 1, and the astigmatism generating lens 6 generates astigmatism. After being
The photodetector 7 receives light. Although not shown, a focusing mechanism that integrally moves the objective lens and the optical element in the optical axis direction is provided (the same applies to the second embodiment below). ,

(Second Embodiment) A second embodiment will be described. FIG. 6 is a schematic configuration diagram of an optical pickup device (the optical information recording / reproducing device incorporating the same is not shown) including the optical element according to the present embodiment. In FIG. 6, a light flux (wavelength λ1 = 610 nm to 670 nm) from the first semiconductor laser 11A as the first light source passes through the beam splitters 12A and 12B, and is a parallel plate having a diffractive structure as shown in FIG. Via element 13
The light enters the objective lens 14 adjacent to it and is focused on the information recording surface of the first optical information recording medium 15A (here, DVD). On the other hand, the light reflected from the first optical information recording medium 15A passes through the objective lens 14, the optical element 13, and the beam splitter 12B, is reflected by the beam splitter 12A in a direction different from that of the first semiconductor laser 11A, and is a photodetector. The light is received at 17A.

On the other hand, in FIG. 6, the luminous flux (wavelength λ2 = 7) from the second semiconductor laser 12A as the second light source is used.
40 nm to 870 nm) passes through the beam splitter 18, is reflected by the beam splitter 12B, and enters the objective lens 14 adjacent thereto via the optical element 13 which is a parallel plate having a diffractive structure as shown in FIG. The light is focused on the information recording surface of the second optical information recording medium 15B (here, CD). On the other hand, the light reflected from the second optical information recording medium 15B passes through the objective lens 14 and the optical element 13, is reflected by the beam splitters 12B and 18, and is received by the photodetector 17B. By forming the semiconductor lasers 11A and 11B on the same substrate and forming them into one unit, a light source of a so-called two-laser-one package can be obtained.

The entire optical system of this embodiment has aberration characteristics as shown in FIG. That is, when a light flux of wavelength λ1 is made incident when using a DVD, the required numerical aperture NA
When the CD is used, when the light flux of wavelength λ2 (> λ1) is incident, the required numerical aperture N
Under-aberration is generated in a region of A2 or more, and so-called flare light is formed. Thereby, it is possible to satisfactorily record or reproduce information on or from different optical information recording media such as DVD and CD.

EXAMPLES Examples of objective lenses suitable for use in the optical pickup device of the above-described embodiment will be described below.

(Example 1) This example is a preferred example of the first embodiment described above. Generally, the diffraction ring zone pitch of the diffractive surface is defined by using a phase difference function or an optical path difference function. Specifically, the phase difference function Φb is represented by the following [Equation 1] with a unit of radian, and the optical path difference function ΦB is represented by [Equation 2] with a unit of mm.

[Equation 1]

[Equation 2]

These two expression methods have different units, but they are equivalent in the meaning of expressing the pitch of the diffraction ring zones. That is, the coefficient b of the phase difference function with respect to the main wavelength λ (unit: mm)
Can be converted to the coefficient B of the optical path difference function by multiplying by λ / 2π,
Conversely, if the coefficient B of the optical path difference function is divided by λ / 2π, it can be converted into the coefficient b of the phase difference function.

Based on the above definition, the optical element, which is a parallel plate, can be provided with power by setting the quadratic coefficient of the phase difference function or the optical path difference function to a value other than zero. In addition, 2 of phase difference function or optical path difference function
The spherical aberration can be controlled by setting a coefficient other than the following, for example, a fourth-order coefficient, a sixth-order coefficient, an eighth-order coefficient, and a tenth-order coefficient to non-zero values. Controlling here means that the spherical aberration of the refracting portion of the objective lens is corrected to have the opposite spherical aberration in the diffracting portion of the optical element to correct the spherical aberration as a whole, or the spherical aberration of the diffracting portion is manipulated. This means setting the total spherical aberration to a desired value.

The objective lens has an aspherical shape represented by the following [Equation 3] on both surfaces thereof.

[Equation 3] Here, Z is an axis in the optical axis direction, h is an axis perpendicular to the optical axis (height from the optical axis: the traveling direction of light is positive), R0 is a paraxial radius of curvature, κ is a conic coefficient, A Is an aspherical surface coefficient, and P is an aspherical power.

Table 1 shows the optical system data of this example.
In addition, after this (including the lens data in the table), a power of 10 (for example, 2.5 × 10 ⁻³ ) is changed to E (for example,
2.5 × E-3) is used.

[Table 1]

Example 2 This example is a preferred example of the second embodiment. Table 2 shows optical data of this example. Laser light having a wavelength of 655 nm is used for the DVD which is the first optical information recording medium, and laser light having a wavelength of 785 nm is used for the CD which is the second optical information recording medium. In the second embodiment, the distance from the first semiconductor laser to the surface of the DVD when recording or reproducing information on the first optical information recording medium (DVD) is the second optical information recording medium ( The distance from the second semiconductor laser to the surface of the CD when recording or reproducing information on (CD) is slightly deviated, but this can be designed to be the same.

[Table 2]

Example 3 This example is a preferred example of the first embodiment. Table 3 shows optical data of this example. This embodiment enables high density optical information recording,
It corresponds to a short wavelength laser called a so-called blue laser.

[Table 3]

[0093]

As described above, according to the present invention,
An optical element that is placed close to a plastic objective lens for high NA, finite magnification, short wavelength applications and that corrects the total deterioration of wavefront aberration (spherical aberration) even when the temperature changes due to wavelength fluctuation of the light source, especially at least one surface It is possible to provide an optical element having a diffractive structure formed therein, an optical pickup device having the optical element, and an optical information recording medium reproducing device.

[Brief description of drawings]

FIG. 1 is a partial cross-sectional view of an objective lens having a diffractive structure formed therein.

FIG. 2 is a partial cross-sectional view of an optical element having a diffractive structure formed therein according to the present invention.

FIG. 3 is a partial cross-sectional view of an optical element having a diffractive structure according to the present invention.

FIG. 4 is a diagram showing a fitted state of an optical element and an objective lens according to the present invention.

FIG. 5 is a schematic configuration diagram of an optical pickup device including the optical system according to the first embodiment.

FIG. 6 is a schematic configuration diagram of a compatible optical pickup device including an optical system according to a second embodiment.

FIG. 7 is a diagram schematically showing optical characteristics of an optical system according to a second embodiment.

[Explanation of symbols]

1 Semiconductor laser 2 beam splitter 3 optical elements 4 Objective lens 5 Optical information recording medium 6 Astigmatism generating lens 7 Photodetector 11A First semiconductor laser 11B Second semiconductor laser 12A, 12B beam splitter 13 Optical element 14 Objective lens 15A, 15B Optical information recording medium 18 Beam splitter 17A, 17B photo detector

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁷ identification code FI theme code (reference) G11B 7/135 G11B 7/135 AZ F term (reference) 2H043 AE04 AE23 2H049 AA03 AA04 AA13 AA14 AA43 AA57 AA64 AA68 2H087 KA13 NA08 NA14 PA01 PA17 PB01 QA02 QA07 QA13 QA34 RA05 RA12 RA13 RA42 RA46 UA01 5D119 AA11 AA22 AA38 AA41 AA43 BA01 BB01 BB02 BB04 EC01 EC45 EC47 FA05 A04 A45 A05 ABB A05 ABB A05 ABB AJA02 A41 A41 A41 A41 A45 A45 A05 A38 A01 FA05 FA08 JA09 JA43 JB01 JB02 JB05

Claims (67)

[Claims] 1. An optical system including a light source having a wavelength λ, an objective lens for focusing a light beam from the light source on an optical information recording medium, and an optical element, and an imaging spot on the optical information recording medium. In an optical element used in an optical pickup device having a photodetector for sensing reflected light, the objective lens of the optical system is a plastic objective lens having a positive refractive power, and the light flux from the light source is The optical element and the plastic objective lens are present in the optical path both when the image is formed on the information recording medium and when the reflected light from the optical information recording medium is incident on the photodetector. A ring-shaped diffractive structure is formed on at least one surface in the effective light beam passage region, and the optical element alone has a paraxial positive refracting power or does not have a refracting power and has a predetermined wavelength. Luminous flux of Compared with the case where the incident optical element used in an optical pickup apparatus characterized in that it has a feature of generating spherical aberration of the under when you than the light flux of the long wavelength side it enters. 2. The optical element used in the optical pickup device according to claim 1, wherein the optical element is arranged adjacent to the plastic objective lens. 3. The sum φD of paraxial powers of the diffractive structure formed on the optical element is −0.1 <φD ·, where f is the combined focal length of the objective lens and the optical element. The optical element used in the optical pickup device according to claim 1 or 2, wherein f <0.0. 4. The optical element according to claim 1, wherein a minimum value pmin of the diffraction pitch within the effective diameter is 5λ <pmin / n <20λ when the utilized diffraction order is represented by n. An optical element used in the optical pickup device described in (1). 5. The optical element used in the optical pickup device according to claim 1, wherein the optical element has a diaphragm function of limiting a diameter of a light beam incident on the objective lens. 6. The optical element used in the optical pickup device according to claim 1, wherein the objective lens is composed of refracting surfaces having aspherical surfaces on both sides. 7. The optical system in which the objective lens and the optical element are combined has a combined focal length f, a numerical aperture NA on the optical information recording medium side, and an imaging magnification m of 2.0 mm <f <5. The optical element used in the optical pickup device according to any one of claims 1 to 6, wherein 0 mm 0.48 <NA <0.65 -1/3 <m ≤ 0 is satisfied. 8. The optical system in which the objective lens and the optical element are combined has a combined focal length f, a numerical aperture NA on the optical information recording medium side, and an imaging magnification m of 0.3 mm <f <1. The optical element used in the optical pickup device according to claim 1, wherein 0 mm 0.75 <NA <0.90 −1/3 <m ≦ 0 is satisfied. 9. The optical element used in the optical pickup device according to claim 1, wherein the optical element is made of a plastic material. 10. The optical element and the objective lens,
It is integrated by fitting, It is characterized by the above-mentioned.
10. An optical element used in the optical pickup device according to any one of items 9 to 9. 11. A first light source having a wavelength λ1 used for recording / reproduction of a first optical information recording medium having a transparent substrate thickness t1, and a second light having a transparent substrate thickness t2 (t2> t1). Wavelength λ2 (λ2> used when recording / reproducing information recording medium)
λ1) a second light source, and an optical system including an objective lens and an optical element for forming an image of the light fluxes from the first and second light sources on the first and second optical information recording media, The first
And an optical element used in an optical pickup device having a photodetector for sensing reflected light of an image forming spot on the second optical information recording medium, wherein the objective lens of the optical system has a positive refractive power. A plastic objective lens having, wherein the plastic objective lens and the optical element are respectively used when the first optical information recording medium is used and when the second optical information recording medium is used, and the light flux from each light source is used for each optical information. When forming an image on a recording medium and when reflected light from each optical information recording medium is incident on the photodetector, the optical element and the plastic objective lens are present in the optical path, and the optical element is , A ring-shaped diffractive structure is formed on at least one surface in the effective light beam passage region, and the optical element alone does not have a positive refractive power or a refractive power paraxially and has a predetermined wavelength. An optical element used in an optical pickup device, which has a characteristic of generating under spherical aberration when a light beam having a wavelength longer than that of a long light beam is incident. 12. The optical element used in the optical pickup device according to claim 11, wherein the optical element is arranged adjacent to the plastic objective lens. 13. A required numerical aperture NA1 of the objective lens when the first optical information recording medium is used, and a required numerical aperture NA2 of the objective lens when the second optical information recording medium is used are NA1> NA2. The optical element has a different diffractive structure design in at least two regions, and one of the boundary positions is located at a position where a ray that defines a required numerical aperture NA2 when the second optical information recording medium is used intersects with the optical element. The optical element used in the optical pickup device according to claim 11 or 12, wherein the optical elements are substantially the same. 14. The sum φD1 of the powers of the diffractive structures formed on the optical element at the wavelength λ1 is −0.1 <φD1 when the combined focal length of the objective lens and the optical element is f1. The optical element used in the optical pickup device according to claim 11, wherein f1 <0.0. 15. The optical element according to claim 11, wherein the minimum value pmin of the diffraction pitch within the effective diameter is 5λ <pmin / n <20λ, where n is the used diffraction order. An optical element used in any one of the optical pickup devices. 16. The optical pickup device according to claim 11, wherein the optical element has a diaphragm function of limiting a light flux having a required numerical aperture NA1 incident on the objective lens. Optical element. 17. The optical element used in the optical pickup device according to claim 11, wherein the objective lens is composed of refracting surfaces having aspherical surfaces on both sides. 18. The combined focal length f at a wavelength λ1 of the optical system including the objective lens and the optical element.
1. The numerical aperture NA1 on the optical information recording medium side and the imaging magnification m1 satisfy 2.0 mm <f1 <5.0 mm 0.48 <NA1 <0.65 −1/3 <m1 ≦ 0, respectively. An optical element used in the optical pickup device according to any one of claims 11 to 17. 19. The optical system in which the objective lens and the optical element are combined has imaging magnifications m1 and m2 at wavelengths λ1 and λ2 of m2 = m1 = 0 or 0.9 <m1 / m2 <1. The optical element used in the optical pickup device according to any one of claims 11 to 18, characterized in that 20. The optical element used in the optical pickup device according to claim 11, wherein the optical element is made of a plastic material. 21. The optical element and the objective lens,
It is integrated by fitting, It is characterized by the above-mentioned.
21. An optical element used in the optical pickup device according to any one of 1 to 20. 22. An optical system comprising a light source of wavelength λ, an objective lens for forming an image of a light beam from the light source on an optical information recording medium, and an optical element, and an image forming spot on the optical information recording medium. In an optical pickup device having a photodetector for sensing reflected light, the objective lens of the optical system is a plastic objective lens having a positive refractive power, and the light flux from the light source is coupled to an optical information recording medium. In both cases of imaging and reflected light from the optical information recording medium entering the photodetector, the optical element and the plastic objective lens are present in the optical path, and the optical element has at least one surface. A ring-shaped diffractive structure is formed in the effective light flux passage area, and the optical element alone has a paraxial positive refracting power or does not have a refracting power, and a light beam of a predetermined wavelength is incident. In case The optical pickup device characterized by having a feature of generating spherical aberration of the under if from the light flux of the long wavelength side it enters. 23. The optical pickup device according to claim 22, wherein the optical element is arranged adjacent to the plastic objective lens. 24. The sum φD of paraxial powers of the diffractive structure formed on the optical element is −0.1 <φD ·, where f is the combined focal length of the objective lens and the optical element. 24. The optical pickup device according to claim 22, wherein f <0.0. 25. The optical element according to claim 22, wherein the minimum value pmin of the diffraction pitch within the effective diameter is 5λ <pmin / n <20λ when the utilized diffraction order is represented by n. An optical pickup device as described in. 26. The optical pickup device according to claim 22, wherein the optical element has a diaphragm function of limiting a diameter of a light beam incident on the objective lens. 27. The optical pickup device according to claim 22, wherein the objective lens is composed of a refracting surface having aspherical surfaces on both sides. 28. In the optical system including the objective lens and the optical element, a combined focal length f, a numerical aperture NA on the optical information recording medium side, and an imaging magnification m are 2.0 mm <f <5. 28. The optical pickup device according to claim 22, wherein 0 mm 0.48 <NA <0.65−1 / 3 <m ≦ 0 is satisfied. 29. In the optical system including the objective lens and the optical element, a combined focal length f, a numerical aperture NA on the optical information recording medium side, and an imaging magnification m are 0.3 mm <f <1. 28. The optical pickup device according to claim 22, wherein 0 mm 0.75 <NA <0.90−1 / 3 <m ≦ 0 is satisfied. 30. The optical pickup device according to claim 22, wherein the optical element is made of a plastic material. 31. The optical element and the objective lens,
It is integrated by fitting, It is characterized by the above-mentioned.
31. The optical pickup device according to any one of 2 to 30. 32. A first light source having a wavelength λ1 used when recording / reproducing a first optical information recording medium having a transparent substrate thickness t1, and a second light having a transparent substrate thickness t2 (t2> t1). Wavelength λ2 (λ2> used when recording / reproducing information recording medium)
λ1) a second light source, and an optical system including an objective lens and an optical element for forming an image of the light fluxes from the first and second light sources on the first and second optical information recording media, The first
And an optical pickup device having a photodetector for sensing the reflected light of the imaging spot on the second optical information recording medium, wherein the objective lens of the optical system is a plastic objective lens having a positive refractive power. Yes, the plastic objective lens and the optical element are used respectively when the first optical information recording medium is used and when the second optical information recording medium is used, and the light flux from each light source forms an image on each optical information recording medium. In both cases, when the reflected light from each optical information recording medium enters the photodetector, the optical element and the plastic objective lens are present in the optical path, and the optical element has a ring on at least one surface. A band-shaped diffractive structure is formed in the effective light beam passage area, and the optical element itself does not have a positive refractive power or a refractive power paraxially. An optical pickup device characterized in that it has a characteristic of generating under spherical aberration when a light beam having a wavelength longer than that is incident. 33. The optical pickup device according to claim 32, wherein the optical element is arranged adjacent to the plastic objective lens. 34. The required numerical aperture NA1 of the objective lens when using the first optical information recording medium and the required numerical aperture NA2 of the objective lens when using the second optical information recording medium are NA1> NA2. The optical element has a different diffractive structure design in at least two regions, and one of the boundary positions is located at a position where a ray that defines a required numerical aperture NA2 when the second optical information recording medium is used intersects with the optical element. 34. The optical pickup device according to claim 32 or 33, which are substantially the same. 35. The sum φD1 of the powers of the diffractive structures formed on the optical element at the wavelength λ1 is −0.1 <φD1.sup.1 when the combined focal length of the objective lens and the optical element is f1. 35. The optical pickup device according to claim 32, wherein f1 <0.0. 36. The optical element according to claim 32, wherein the minimum value pmin of the diffraction pitch within the effective diameter is 5λ <pmin / n <20λ, where n is the used diffraction order. The optical pickup device according to any one of claims. 37. The optical pickup device according to claim 32, wherein the optical element has a diaphragm function of limiting a light flux having a required numerical aperture NA1 incident on the objective lens. 38. The optical pickup device according to claim 32, wherein the objective lens is composed of a refracting surface having aspherical surfaces on both sides. 39. A composite focal length f at a wavelength λ1 of the optical system including the objective lens and the optical element.
1. The numerical aperture NA1 on the optical information recording medium side and the imaging magnification m1 satisfy 2.0 mm <f1 <5.0 mm 0.48 <NA1 <0.65 −1/3 <m1 ≦ 0, respectively. The optical pickup device according to any one of claims 32 to 38, which is characterized in that. 40. In the optical system including the objective lens and the optical element, the imaging magnifications m1 and m2 at wavelengths λ1 and λ2 are: m2 = m1 = 0 or 0.9 <m1 / m2 <1. The optical pickup device according to any one of claims 32 to 39, characterized in that 41. The optical pickup device according to claim 32, wherein the optical element is made of a plastic material. 42. The optical element and the objective lens,
It is integrated by fitting, It is characterized by the above-mentioned.
42. The optical pickup device according to any one of 2 to 41. 43. The optical pickup device according to claim 32, wherein the first light source and the second light source are constituted by a single unit. 44. The distance from the first light source to the surface of the first optical information recording medium when recording or reproducing information on the first optical information recording medium is the second optical information recording medium.
5. The distance from the second light source to the surface of the second optical information recording medium when recording or reproducing information on or from the optical information recording medium is substantially equal to the distance.
3. The optical pickup device according to item 3. 45. An optical system comprising a light source of wavelength λ, an objective lens for forming an image of a light beam from the light source on an optical information recording medium, and an optical element, and an image forming spot on the optical information recording medium. In an optical information recording / reproducing apparatus including an optical pickup device having a photodetector for sensing reflected light, the objective lens of the optical system is a plastic objective lens having a positive refracting power, and the light flux from the light source is When the image is formed on the optical information recording medium, and in any case when the reflected light from the optical information recording medium enters the photodetector, the optical element and the plastic objective lens are present in the optical path, and In the optical element, a ring-shaped diffractive structure is formed on at least one surface in the effective light flux passage area, and the optical element alone has a paraxial positive refracting power or does not have a refracting power, Wavelength of Compared with the case where the light flux is incident, the optical information recording and reproducing apparatus characterized by having the property of generating a spherical aberration of the under if from the light flux of the long wavelength side it enters. 46. The optical information recording / reproducing apparatus according to claim 45, wherein the optical element is arranged adjacent to the plastic objective lens. 47. The sum φD of paraxial powers of the diffractive structure formed on the optical element is −0.1 <φD ·, where f is a combined focal length of the objective lens and the optical element. The optical information recording / reproducing apparatus according to claim 45 or 46, wherein f <0.0. 48. The optical element according to claim 45, wherein the minimum value pmin of the diffraction pitch within the effective diameter is 5λ <pmin / n <20λ when the utilized diffraction order is represented by n. An optical information recording / reproducing apparatus according to claim 1. 49. The optical information recording / reproducing apparatus according to claim 45, wherein the optical element has a diaphragm function of limiting a diameter of a light beam incident on the objective lens. 50. The optical information recording / reproducing apparatus according to claim 45, wherein the objective lens is composed of a refracting surface having aspherical surfaces on both sides. 51. In the optical system including the objective lens and the optical element, a combined focal length f, a numerical aperture NA on the optical information recording medium side, and an imaging magnification m are 2.0 mm <f <5. The optical information recording / reproducing apparatus according to any one of claims 45 to 50, wherein 0 mm 0.48 <NA <0.65 -1/3 <m ≤ 0 is satisfied. 52. In the optical system including the objective lens and the optical element, a combined focal length f, a numerical aperture NA on the optical information recording medium side, and an imaging magnification m are 0.3 mm <f <1. The optical information recording / reproducing apparatus according to claim 45, wherein 0 mm 0.75 <NA <0.90 −1/3 <m ≦ 0 is satisfied. 53. The optical information recording / reproducing apparatus according to claim 45, wherein the optical element is made of a plastic material. 54. The optical element and the objective lens,
It is integrated by fitting, It is characterized by the above-mentioned.
The optical information recording / reproducing apparatus according to any one of 5 to 53. 55. A first light source having a wavelength λ1 used for recording / reproducing of a first optical information recording medium having a transparent substrate thickness t1, and a second light having a transparent substrate thickness t2 (t2> t1). Wavelength λ2 (λ2> used when recording / reproducing information recording medium)
λ1) a second light source, and an optical system including an objective lens and an optical element for forming an image of the light fluxes from the first and second light sources on the first and second optical information recording media, The first
And an optical pickup device having an optical pickup device for sensing the reflected light of the imaging spot on the second optical information recording medium, wherein the objective lens of the optical system has a positive refraction. A plastic objective lens having power, wherein the plastic objective lens and the optical element are used respectively when the first optical information recording medium is used and when the second optical information recording medium is used, and the luminous flux from each light source is The optical element and the plastic objective lens are present in the optical path both when the image is formed on the optical information recording medium and when the reflected light from each optical information recording medium enters the photodetector. The element has a ring-shaped diffractive structure formed on at least one surface in the effective light beam passage area, and does not have a positive refractive power or a refractive power paraxially as an optical element alone. The optical information recording / reproducing apparatus is characterized in that it has a characteristic of generating an under spherical aberration when a light beam having a wavelength longer than that of a light beam having a wavelength of is incident. 56. The optical information recording / reproducing apparatus according to claim 55, wherein the optical element is arranged adjacent to the plastic objective lens. 57. A required numerical aperture NA1 of the objective lens when the first optical information recording medium is used, and a required numerical aperture NA2 of the objective lens when the second optical information recording medium is used are NA1> NA2. The optical element has a different diffractive structure design in at least two regions, and one of the boundary positions is located at a position where a ray that defines a required numerical aperture NA2 when the second optical information recording medium is used intersects with the optical element. 57. The optical information recording / reproducing apparatus according to claim 55 or 56, which are substantially the same. 58. The sum φD1 of the powers of the diffractive structures formed on the optical element at the wavelength λ1 is −0.1 <φD1 · when the combined focal length of the objective lens and the optical element is f1. 58. The optical information recording / reproducing apparatus according to claim 55, wherein f1 <0.0. 59. The optical element according to claim 55, wherein a minimum value pmin of a diffraction pitch within an effective diameter is 5λ <pmin / n <20λ, where n is a used diffraction order. An optical information recording / reproducing apparatus according to any one of the above. 60. The optical information recording / reproducing apparatus according to claim 55, wherein the optical element has a diaphragm function for limiting a light beam having a required numerical aperture NA1 incident on the objective lens. . 61. The optical information recording / reproducing apparatus according to claim 55, wherein the objective lens is composed of a refracting surface having aspherical surfaces on both sides. 62. The optical system including the objective lens and the optical element has a combined focal length f at a wavelength λ1.
1. The numerical aperture NA1 on the optical information recording medium side and the imaging magnification m1 satisfy 2.0 mm <f1 <5.0 mm 0.48 <NA1 <0.65 −1/3 <m1 ≦ 0, respectively. The optical information recording / reproducing apparatus according to any one of claims 55 to 61, characterized in that: 63. In the optical system including the objective lens and the optical element, the imaging magnifications m1 and m2 at wavelengths λ1 and λ2 are: m2 = m1 = 0 or 0.9 <m1 / m2 <1. The optical information recording / reproducing apparatus according to any one of claims 55 to 62, characterized in that 64. The optical information recording / reproducing apparatus according to claim 55, wherein the optical element is made of a plastic material. 65. The optical element and the objective lens,
6. The device is integrated by fitting.
The optical information recording / reproducing apparatus according to any one of 5 to 64. 66. The optical information recording / reproducing apparatus according to claim 55, wherein the first light source and the second light source are composed of a single unit. 67. The distance from the first light source to the surface of the first optical information recording medium when recording or reproducing information on the first optical information recording medium is the second distance.
7. The distance from the second light source to the surface of the second optical information recording medium when recording or reproducing information on or from the optical information recording medium according to claim 6, is approximately equal to
6. The optical information recording / reproducing apparatus according to item 6.