JPH1083562A - Optical pickup device, recording/reproducing objective single lens and information reproducing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a proper numerical aperture according to different kinds of recording media with simple optical constitution by varying a divergent degree of luminous flux incident on an objective lens. SOLUTION: The luminous flux from a laser light source 1 is converged on a recording surface 8 after passing through a beam splitter 2, a moving lens 3, a diaphragm 5 and the objective lens 6 and then a substrate 7. The reflected light modulated by an information pit on the recording surface 8 reversely tracks an outward light path, arrives at the beam splitter 2 and enters into a photodetector 9 being a light receiving means after the optical path is separated. In this case, the moving lens 3 is a luminous flux divergent degree revision means, and is moved in the optical axial direction by a lens moving means 21 corresponding to the kind of the recording media of the recording surface 8. For instance, according to a DVD of the thickness 0.6mm of the transparent substrate 7 of the recording medium or a CD of the thickness 1.2mm, the moving lens 3 is moved to a position close to the objective lens, or the position close to the laser light source, and the required numerical aperture, e.g. NA=0.6 or 0.37, etc., is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a condensing optical system for an optical disc for recording and / or reproducing optical information by irradiating a light beam such as a laser beam onto an optical information recording medium (hereinafter also referred to as an optical disc). In particular, the present invention relates to a condensing optical system for recording and / or reproducing a high-density optical disc, an objective single lens used in such a condensing optical system, and an information reproducing method.

[0002]

2. Description of the Related Art A conventional technique according to the present invention will be described. In recent years, along with the practical use of short-wavelength red semiconductor lasers, the development of DVDs (digital video discs), which are high-density optical information recording media with the same optical disc size and larger capacity as conventional CDs (compact discs), has been developed. It is progressing. This DVD optical disk (hereinafter simply referred to as DVD
When a short-wavelength semiconductor laser of 635 nm or 650 nm is used, the numerical aperture NA of the pickup objective lens on the optical disk side is set to 0.6. Also, the thickness of the disk substrate is 0.6 mm, which is half that of the conventional CD.
And Further, the track pitch is 0.74 μm, the shortest pit length is 0.4 μm, and the track pitch of CD is 1.6 μm.
m and the minimum pit length is 0.83 μm or less.

[0003] In addition to DVDs and CDs, optical disks of various standards have been commercialized. Magneto-optical disk (M
In O), an optical disk having a recording capacity of 128 MB, 230 MB, or 640 MB for a 3.5-inch ISO standard is commercialized, and the disk substrate thickness is 1.2 m.
m. For example, in order to record / reproduce an MO of 230 MB, a laser light source having a wavelength of about 780 nm is used, and a diffraction-limited focusing optical system having an NA of about 0.55 on the optical disk side is used. To record / reproduce an 640 MB MO, a laser light source having a wavelength of about 680 nm is used, and a diffraction-limited focusing optical system with an NA of about 0.55 on the optical disk side is used.

Further, in the field of recent MOs, products of HS standards different from the ISO standards have been commercialized, which have a recording capacity of 640 MB and a substrate thickness of 0.8 mm. For this purpose, a laser light source having a wavelength of about 680 nm is used, and a diffraction-limited focusing optical system having an NA of about 0.55 on the optical disk side is used. In addition, laser disks (LDs), MDs, PDs, etc. are also widely used, and 5.2
5 inch size magneto-optical disks and 12 inch size disks have also been commercialized mainly for business use. Further, an optical disk having a higher recording density is being developed by utilizing a technology of shortening the wavelength of a laser light source represented by SHG, a blue semiconductor laser, or the like.

[0005] As described above, in the market, size, substrate thickness,
In an era when various optical disks having different recording densities and wavelengths are present, an optical pickup device that can cope with various optical disks will be important in the future.

Various optical pickup devices corresponding to a plurality of optical disks have been proposed so far. One is a method of switching and using a plurality of optical pickup devices corresponding to respective optical disks. As another method, when two types of optical discs, DVD and CD, are supported, a method of switching between an objective lens and an aperture corresponding to each optical disc as shown in the configuration diagram of the conventional optical pickup device of FIG. It has been known.

Here, the optical pickup device of FIG. 1 will be briefly described. In the figure, when playing a DVD,
A light beam emitted from the laser light source 1 (having a wavelength of 635 nm to 650 nm) passes through the hologram beam splitter 2 and enters the lens 3, becomes a parallel light beam, exits the objective lens 6 at the diaphragm 5, and goes toward the DVD. Is 0.
The luminous flux is restricted to about 6 and the light enters the objective lens 6. The objective lens 6 is provided with a substrate (disk substrate, here, t = 0.
6 mm) through 7 to form an aberration-free light spot on the information recording surface 8
Image up.

The light beam modulated and reflected by the information pits on the information recording surface 8 returns to the hologram beam splitter 2 via the objective lens 6 and the lens 3, where it is separated from the optical path from the laser light source 1 and detected. Incident on the vessel 9. The photodetector 9 is a multi-divided PIN photodiode, and outputs a current proportional to the intensity of the incident light beam from each element and sends the current to a detection circuit (not shown), where the information signal and the focus signal are output. An error signal and a track error signal are generated. Based on the focus error signal and the track error signal, the objective lens 6 is driven by a two-dimensional actuator (not shown) including a magnetic circuit and a coil.
Is controlled in the focusing direction and the tracking direction, and the light spot position is always adjusted on the information track.

Next, when a CD is used for reproduction instead of a DVD, an actuator section surrounded by a dotted line in the figure is switched to an objective lens 11 and an aperture 10 corresponding to the CD for reproduction. In this case, the wavelength of the laser light source is 635 (nm).
When using a CD, the NA required for CD playback is 0.
It is about 38. In the case of this CD, the collimator lens 3
Are emitted from the objective lens 11 at the stop 10 and are restricted so that the numerical aperture of the light beam toward the CD is about 0.38, and then enter the objective lens 11. When the parallel light beam enters the objective lens 11, the substrate 7 (disc substrate, here, t = 1.2 m
Through m), an aberration-free light spot is imaged on the information recording surface 8.

[0010] Each of the above two methods requires a plurality of types of objective lenses, but various methods for reproducing a plurality of optical disks with one objective lens have been proposed.

In the method described in Japanese Patent Application Laid-Open No. 8-55363, when the wavelength is 635 nm, a first optical disk having a numerical aperture required for reproduction of 0.6 and a substrate thickness of 0.6 mm is provided. In consideration of the second optical disk having a different corresponding wavelength, two light sources are used, and the wavefront aberration of the imaging spot is 0.01λrm for both optical disks.
An example of the arrangement is as follows. When the second optical disc is a CD-R, a light source having a wavelength of 635 nm is used for the first optical disc, a light source having a wavelength of 780 nm is used for the second optical disc, and the objective lens is emitted. The aperture is provided so that the numerical aperture of the light beam is optimal for reproduction.

Lecture No. 18 at the 21st Optical Symposium hosted by the Japan Optical Society of Japan Society of Applied Physics
The paper "Objective optical system with variable thickness of disc substrate" published in P45-P48
A method of correcting a spherical aberration caused by a change in substrate thickness by moving a positive correction lens relative to an objective lens in an optical axis direction is shown.

Assuming that the wavelength to be used is 650 nm, an objective lens whose aberration is well corrected with a substrate thickness of 0.6 mm and a numerical aperture of 0.6 is used, and a light source, a correction lens, an aperture stop,
In the first arrangement of the objective lens and the optical disk having a substrate thickness of 0.6 mm, a stop is used so that the numerical aperture of the light beam emitted from the objective lens is 0.6, and the lens is almost aberration-free. Similarly, in the second arrangement including the light source, the correction lens, the aperture stop, the objective lens, and the optical disk having a substrate thickness of 1.2 mm, the correction lens is moved to the light source side, and the numerical aperture of the light beam emitted from the objective lens is reduced. A stop with a value of 0.375 is used, and there is almost no aberration in this range.

"International symp
osium on optical memory an
d optical data storage 19
96, "Dual Wavelength Optic", which was published under the lecture number OThC4-1 and published in Technical Digests 323p to 325p.
al Head for 0.6mm and 1.2
The mm Substrate Thickness uses two light sources and an objective lens designed for a common substrate thickness of 0.6 mm, and has a first wavelength of 63 mm.
Two types of optical systems have been proposed: a DVD with a light source of 5 nm and a CD with a light source of a second wavelength of 785 nm.

In the first method, a hologram optical element is arranged in a parallel light beam, and a light beam of 635 nm is transmitted as it is as a zero-order diffracted light at a hologram portion, and is transmitted at 785 nm.
Is converted as a first-order diffracted light into a light that corrects spherical aberration caused by a difference in substrate thickness. The diameter of the hologram portion is set so that a 785 nm light beam passes through the objective lens and has a numerical aperture of 0.45. 635n
The luminous flux of m passes through the objective lens and the substrate and is converted into a luminous flux having a numerical aperture of 0.6 and having no aberration. The 785 nm light beam passes through the objective lens and the substrate and is converted into an aberration-free light beam with a numerical aperture within 0.45. A light beam having a numerical aperture of 0.45 or more has a large spherical aberration, and therefore becomes a flare on the information recording surface.

In the second method, as disclosed in Japanese Patent Application Laid-Open No. 8-55363, a light beam of 635 nm is incident on the objective lens as a parallel light beam, while a light beam of 785 nm is viewed from the objective lens. They are arranged so that the magnification is −0.065, and are converged on the information recording surface as a beam having no aberration for both DVD and CD.

At this time, a variable aperture called 785 nm
Of the luminous flux passes through the objective lens and the substrate, and has a numerical aperture of 0.1.
An optical element provided with an interference filter on an annular zone for reflecting a light beam of 45 or more is inserted on the light source side of the objective lens. In addition, this interference filter is configured to transmit light of 635 nm. As a result,
The 635 nm light beam passes through the objective lens and the substrate and has a numerical aperture of 0.6 and becomes an aberration-free light beam. The 785 nm light beam passes through the objective lens and the substrate and has a numerical aperture of 0.45 or less and becomes an aberration-free light beam.

However, in the method described in Japanese Patent Application Laid-Open No. 8-55363, the light beam from the laser light source for reproducing the CD is set so that the numerical aperture of the light beam emitted from the objective lens is optimal for reproduction. Therefore, when the objective lens moves in the direction perpendicular to the optical axis, the amount of light returning to the photodetector decreases, the tracking range decreases, and it becomes difficult to reproduce a CD with large eccentricity.

Lecture No. 18 at the 21st Optical Symposium hosted by the Japan Optical Society of Japan Society of Applied Physics
Can cope with various optical disks having different substrate thicknesses, but an aperture stop adjusting device and a stop inserting device are required.

"International symp
osium on optical memory an
d optical data storage 19
The method presented at the lecture number OThC4-1 in "96" requires a hologram optical element and a variable aperture.

In a conventional objective lens, a stop for restricting a light beam is provided in a lens frame separately from a plurality of lenses. Then, in this type of optical system, one objective single lens is formed by using an aspheric surface. It has become commonplace to be used. Such an objective single lens is a molded product of plastic or glass, and unlike a polished spherical single lens, if the outer diameter is not large relative to the effective diameter, the surface accuracy within the effective diameter deteriorates, and there is a problem. Was. Therefore, apart from the objective single lens, the optical information pickup is provided with a diaphragm for restricting the light flux. This diaphragm is a separate component, and must be incorporated so as not to cause a misalignment with the optical axis of the objective single lens, which has been costly in parts and assembly.

[0022]

However, assuming that a combination of the above-mentioned conventional methods is applicable to various optical disks having different substrate thicknesses, recording densities, and operating wavelengths, it is necessary to switch to a plurality of aperture diameters. This requires an insertion / switching mechanism, a variable stop device, or a special optical element using a hologram or an interference filter, resulting in an extremely complicated pickup device.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to realize various optical disks having different substrate thicknesses and recording densities without complicating a pickup device by using one objective lens. Further, if the laser wavelength to be used is limited due to problems such as reflectivity, it is unavoidable to use a plurality of laser light sources, but even in such a case, the object is to realize an extremely simple optical system. In particular, an optical system that does not require the insertion of an aperture stop or an aperture stop adjustment device, and that does not have the problem that it is difficult to reproduce a CD with a large eccentricity due to a reduction in tracking range due to the shaking by the fixed stop. It is intended to be. Further, it is intended to provide a simpler structure by omitting an aperture provided on the light source side of the objective lens.

[0024]

The above object is achieved by the following constitution. That is, an optical pickup device according to the first aspect of the present invention includes a laser light source, an objective lens having a positive refractive power for condensing a light beam from the laser light source on an information recording surface of an optical information recording medium, and Light receiving means for receiving a light beam reflected by a surface and passing through the objective lens,
In an optical pickup device for an optical information recording medium having divergence changing means for changing a divergence of a light beam incident on the objective lens, a wavelength of a laser light source is λ, and a light beam having a numerical aperture of NA or less is incident on an information recording surface. Wavefront aberration RM
When the spherical aberration component of the S value is WSA (NA), the required numerical aperture of the objective lens on the optical information recording medium side to obtain a light spot at wavelength λ from which information can be read for the first optical information recording medium is When NA1 is set, the numerical aperture of the light beam emitted from the objective lens is N for the first optical information recording medium.
A1 and the following condition are satisfied: WSA (NA1) <0.05λ Further, the second optical information recording medium is provided with an objective lens on the optical information recording medium side for obtaining a light spot at a wavelength λ from which information can be read. When the required numerical aperture is NA2, the divergence of the light beam incident on the objective lens by the divergence changing means is set to the first light so that the following condition is satisfied for the second optical information recording medium. It is characterized by being different from the case of the information recording medium.

NA1> 1.1NA2 0.03λ <WSA (NA2) <0.12λ WSA (1.1NA2) / WSA (NA2)> 1.2 The optical pickup device according to the second aspect of the present invention includes a laser light source and a laser light source. An objective lens having a positive refractive power for condensing a light beam from a laser light source onto an information recording surface via a transparent substrate of an optical information recording medium, and a light beam reflected by the information recording surface and passing through the objective lens. In an optical pickup device for an optical information recording medium having a light receiving means for receiving light and a divergence changing means for changing a divergence of a light beam incident on the objective lens, the wavelength of the laser light source is λ, and the light beam emitted from the objective lens has an aperture. The spherical aberration component of the wavefront aberration RMS value when a light flux of several NA or less passes through a transparent substrate is represented by WSA (NA).
When the required numerical aperture of the objective lens on the optical information recording medium side for obtaining a light spot at which the information can be read from the first optical information recording medium at the wavelength λ is NA1, the first optical information For the recording medium, the numerical aperture of the light beam emitted from the objective lens is NA1 and satisfies the following condition: WSA (NA1) <0.05λ Further, the first optical information recording medium is a transparent substrate having a thickness of When the required numerical aperture of the objective lens on the optical information recording medium side for obtaining a light spot at which the information can be read from the second optical information recording medium at a wavelength λ is different from that of the second optical information recording medium, the second optical information recording medium On the other hand, the divergence changing means makes the divergence of the light beam incident on the objective lens different from that of the first optical information recording medium so as to satisfy the following condition.

NA1> 1.1NA2 0.03λ <WSA (NA2) <0.12λ WSA (1.1NA2) / WSA (NA2)> 1.2 The optical pickup device according to the third aspect of the present invention comprises a laser light source and a laser light source. An objective lens having a positive refractive power for condensing a light beam from a laser light source onto an information recording surface via a transparent substrate of an optical information recording medium, and a light beam reflected by the information recording surface and passing through the objective lens. In an optical pickup device for an optical information recording medium having a light receiving means for receiving light and a divergence changing means for changing a divergence of a light beam incident on the objective lens, the wavelength of the laser light source is λ, and the light beam emitted from the objective lens has an aperture. The spherical aberration component of the wavefront aberration RMS value when a light flux of several NA or less passes through a transparent substrate is represented by WSA (NA).
When the required numerical aperture of the objective lens on the optical information recording medium side for obtaining a light spot at which the information can be read from the first optical information recording medium at the wavelength λ is NA1, the first optical information For the recording medium, the numerical aperture of the light beam emitted from the objective lens is NA1, and the light from which information can be read on a second optical information recording medium having a transparent substrate different in thickness from the first optical information recording medium. The necessary numerical aperture on the optical information recording medium side of the objective lens for obtaining a spot with a wavelength λ is NA2.
Where NA1> 1.1NA2, and for the second optical information recording medium, the divergence changing means uses the objective lens in order to obtain an optimal light spot for reading the recorded information. Is characterized in that the divergence of a light beam incident on the first optical information recording medium is different from that of the first optical information recording medium.

According to a fourth aspect of the present invention, there is provided an optical pickup device comprising: a first laser light source, a second laser light source, and a light source for condensing a light beam from the laser light source on an information recording surface of an optical information recording medium. In an optical pickup device for an optical information recording medium, comprising: an objective lens having a refractive power of, and light receiving means for receiving a light beam reflected by the information recording surface and passing through the objective lens, the wavelength of the first laser light source is set to λ1 When a spherical aberration component of a wavefront aberration RMS value of a light beam having a numerical aperture NA or less is set to WSA (NA) with respect to a light beam incident on the information recording surface, a light spot from which information can be read from the first optical information recording medium is determined. When the required numerical aperture of the objective lens on the optical information recording medium side for obtaining the wavelength λ1 is NA1, the numerical aperture of the light beam emitted from the objective lens is NA for the first optical information recording medium. 1 and the following condition is satisfied, WSA (NA1) <0.05λ1 Further, an optical spot on the optical information recording medium side of the objective lens for obtaining, at a wavelength λ2, a light spot from which information can be read for the second optical information recording medium. When the required numerical aperture is NA2, NA1> 1.1NA2, and the divergence of the second light flux incident on the objective lens for the second optical information recording medium so as to satisfy the following condition. And the divergence of the first luminous flux.

0.03λ <WSA (NA2) <0.12λ2 WSA (1.1NA2) / WSA (NA2)> 1.2 The optical pickup apparatus according to the fifth aspect of the present invention provides a first laser light source and a second laser light source. A laser light source, an objective lens having a positive refractive power for condensing a light beam from the laser light source on an information recording surface of an optical information recording medium, and a light beam reflected by the information recording surface and passing through the objective lens In the optical pickup device for an optical information recording medium having light receiving means for receiving light, an object for obtaining a wavelength of the first laser light source at λ1, and an optical spot at which information can be read from the first optical information recording medium at the wavelength λ1. When the required numerical aperture of the lens on the optical information recording medium side is NA1, the first light flux is used for the first optical information recording medium, and the numerical aperture of the light flux emitted from the objective lens is NA1. Ri, further necessary numerical aperture on the optical information recording medium side of the objective lens for obtaining a light spot at the wavelength λ2 can be read the information for the second optical information recording medium NA2
Where NA1> 1.1NA2, and for the second optical information recording medium, the second light flux is used to obtain an optimal light spot for reading recorded information. The divergence of the light beam incident on the objective lens is different from that of the first light beam.

According to a sixth aspect of the present invention, there is provided a recording / reproducing objective single lens which converges a laser beam and an almost aberration-free light beam from the laser beam source onto an information recording surface via a transparent substrate of an optical information recording medium. For recording / reproducing an optical information recording medium of an optical pickup device for an optical information recording medium having an objective single lens having a positive refractive power and a light receiving means for receiving a light beam reflected by the information recording surface and passing through the objective single lens. When the wavelength of the laser light source in the objective single lens is λ, and the required numerical aperture on the optical information recording medium side of the objective single lens for obtaining an optical spot at which the optical information recording medium can read information at the wavelength λ is NA1, Assuming that the effective radius of the light source side surface of the light flux having a numerical aperture NA1 emitted from the single lens is H1, the light flux incident at least in the range from H1 to 1.02H1 passes through the objective single lens. Wavefront aberration RM of a light beam having an incident height H or less incident on an objective lens through a transparent substrate
The spherical aberration component of the S value is WSA (H), and the following conditions are satisfied.

WSA (H1) <0.05λ WSA (1.02H1) / WSA (H1)> 1.2 The recording / reproducing objective single lens according to the seventh aspect of the present invention comprises a laser light source and a laser light source. An objective single lens having a positive refractive power for converging an aberration-free light beam onto the information recording surface via the transparent substrate of the optical information recording medium, and receiving a light beam reflected by the information recording surface and passing through the objective lens In a single objective lens for recording / reproducing of an optical information recording medium of an optical pickup device for an optical information recording medium having a light receiving means, a wavelength of a laser light source is obtained as λ, and a light spot from which information can be read out of the optical information recording medium is obtained as wavelength λ. When the required numerical aperture of the objective single lens on the optical information recording medium side for
Assuming that the effective radius of the light source side surface of the light beam having the numerical aperture NA1 emitted from the objective single lens is H1, the light beam incident at least in the range from H1 to 1.02H1 is transmitted through the objective single lens and When a vertical spherical aberration at an incident height H incident on the lens is defined as SA (H), the following condition is satisfied.

| SA (1.02H1) |> 8λ / (NA1) ^{2 In} the optical pickup device according to the eighth aspect of the present invention, an optical path from the laser light source through the information recording surface to the photodetector is: It is characterized in that a ring-shaped light beam shielding portion is provided for shielding a light beam passing through a range larger than NA2 and smaller than NA1 from entering the photodetector.

According to a ninth aspect of the present invention, in the optical pickup device, the light beam passing through a range larger than NA2 and smaller than NA1 is applied to the surface of the objective lens on the side of the laser light source or the surface of the optical information recording medium. It is characterized in that a ring-shaped light beam shielding portion for shielding the light from entering the detector is provided.

In the optical pickup device according to the tenth aspect of the present invention, the photodetector is divided into a portion capable of receiving a light beam passing through the range of NA2 and a portion capable of receiving a light beam passing between NA1 and NA2. And a plurality of light receiving elements.

The information reproducing method according to the eleventh aspect of the present invention is characterized in that:
A light beam emitted from a laser light source is condensed as a light spot on an information recording surface of an optical information recording medium by a condensing optical system, and reflected light from the information recording surface is received by a photodetector, and the optical information recording medium In an information reproducing method for reproducing information recorded on the information recording surface, the wavelength of the light beam emitted from the laser light source is λ, with respect to the light beam incident on the information recording surface,
Assuming that the spherical aberration component of the wavefront aberration RMS value of a light beam having a numerical aperture NA or less is WSA (NA), WSA (NA1) <0 in the range of the numerical aperture NA1 on the information recording surface side as the condensing optical system. .05λ when using a condensing optical system capable of obtaining a first light spot, and reproducing information from a second light spot having a diameter larger than the first light spot. Is characterized in that information is reproduced by obtaining the second light spot by generating spherical aberration.

According to the twelfth aspect of the present invention, there is provided an information reproducing method comprising:
A light beam emitted from a laser light source is condensed as a light spot on an information recording surface of an optical information recording medium by a condensing optical system, and reflected light from the information recording surface is received by a photodetector, and the optical information recording medium In an information reproducing method for reproducing information recorded on the information recording surface, the wavelength of the light beam emitted from the laser light source is λ, with respect to the light beam incident on the information recording surface,
Assuming that the spherical aberration component of the wavefront aberration RMS value of a light beam having a numerical aperture NA or less is WSA (NA), WSA (NA1) <0 in the range of the numerical aperture NA1 on the information recording surface side as the condensing optical system. .05λ when using a condensing optical system capable of obtaining a first light spot, and reproducing information from a second light spot having a diameter larger than the first light spot. Where NA1> 1.1NA2 0.03λ <WSA (NA2) <0.12λ WSA, where NA2 is the numerical aperture NA2 on the information recording surface side of the condensing optical system necessary to obtain the second light spot. Information is reproduced by generating a spherical aberration that satisfies the condition of (1.1NA2) / WSA (NA2)> 1.2.

The information reproducing method according to the thirteenth aspect of the present invention,
The condensing optical system has at least an objective lens, and generates a spherical aberration by changing the divergence of a light beam incident on the objective lens.

[0037]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Prior to the description of embodiments of the present invention, data of an existing optical disk used for the description and an example of a conventional example for comparison will be described.

First, the optical disk will be described. Assuming that the optical disc is reproduced by the focused spot of diffraction-limited performance, the working wavelength λ and the numerical aperture NA of the light beam emitted from the condensing optical system, or the ratio between them, are standardized for each optical disc. It is desirable to satisfy it.

In the present invention, an existing main optical disk will be described using the following values.

[0040]

[Table 1]

When a stigmatic light beam having a uniform light energy distribution is incident on the stigmatic focusing optical system, the focusing spot is
There are a plurality of ring-shaped spots whose intensity is 0 with respect to the center intensity.

The radius of the ring having the smallest intensity of zero is represented by 0.61λ / NA from diffraction theory. FIG. 2 shows a spot simulation diagram of the aberration-free optical system, where λ = 780 nm and NA 0.45.

As a criterion for judging the quality of a spot, let r1 be the spot radius at which the center intensity is 1 / e2 and let α1 be the ratio of the maximum intensity of the side lobe to the center intensity. In this case, r1 = 0.72 μm, α1 = 1.8%. In general, when α1 ≧ 13%, the jitter due to the side rope deteriorates.

Next, an example of a conventional optical system is shown here for comparison. The symbols used are as follows.

Ri: radius of curvature of the i-th surface from the light source side di: thickness or interval on the optical axis between the i-th surface and the (i + 1) -th surface from the light source side ni: i-th surface from the light source side The refractive index at the used wavelength of the medium between the surface and the (i + 1) th surface. The aspherical shape of the lens surface is as follows. In an orthogonal coordinate system in which the vertex of the surface is the origin and the optical axis direction is the X axis, κ is a cone Coefficient, A
i is an aspherical coefficient, and Pi (4 ≦ Pi) is represented by the following “Equation 1”, where Pi is a power of the aspherical surface.

[0046]

(Equation 1)

(Conventional example) A conventional example is disclosed in Japanese Patent Application Laid-Open No. H8-5536.
This is an optical system that assumes No. 3 publication. Such an optical system can be designed so as to have no aberration by using an aspherical lens as the collimator. In addition, N on the light source side of the collimator
Since A is small, the light flux from the collimator is
Even if the light source is arranged on the collimator side along the optical axis of the collimator from the focal point on the light source side of the collimator so that the light is slightly divergent, the generated spherical aberration is slight. Therefore, only the objective lens is described here.

Next, Tables 2 and 3 show optical data.

[0049]

[Table 2]

[0050]

[Table 3]

FIG. 3 shows a spherical aberration diagram of DVD and CD, and FIG. 4 shows a spot simulation of DVD at a defocus position where the best spot shape is obtained.
FIG. 5 shows the results of CD spot simulation at the defocus position where the best spot shape is obtained.

For DVD, r1 = 0.44 μm,
With respect to α1 = 1.8% CD, r1 = 0.72 μm, α1 = 1.8%, and both DVD and CD have perfect spot values.

FIG. 6 shows a spot simulation of a CD, which shows the result of a spot simulation of a CD when the same aperture diameter as that of a DVD is used. At this time, r1 = 0.56 μm, α1 = 2.1%, that is, a spot corresponding to NA = 0.58. As described above, the reproduction signal is deteriorated because the aperture is narrowed down by more than 30%. The effect of tilting the optical disk is proportional to the cube of NA, but this is a problem for a CD having a large warpage.

Therefore, in this optical system, when reproducing a CD, it is necessary to set an aperture for CD reproduction in place of the aperture used for DVD.

The optical characteristics required for the optical pickup device may be such that a spot having an optimum shape for reading information is converged on the information recording surface, and may not necessarily have the diffraction-limited performance due to a non-aberration light beam.

In a lens having a step on the optical surface, the wavefront is discontinuous and the wavefront aberration is significantly increased. However, as in the objective lens described in Japanese Patent Application Laid-Open No. It can be divided into a plurality of areas or “International symposium”
mon optical memory andop
The objective lens optimized for DVD, such as the objective lens presented in the lecture number OFA3-1 of "Tomic Data Storage 1996", has a ring-shaped shield, and the RMS value of the wavefront aberration cannot be defined.

However, the spots obtained by both of them can be comparable to spots of diffraction-limited performance at the optimum defocus position.

The spherical aberration component of wavefront aberration can be controlled by changing the divergence of the light beam incident on the objective lens. Regardless of the objective lens, it changes the divergence of the light beam incident on the objective lens. That is, the spot shape can be controlled by changing the spherical aberration component of the wavefront aberration.

The wavelength of the laser light source is λ, and the required numerical aperture on the optical information recording side of the converging optical system for obtaining a light spot from the first optical information recording medium for reading information at the wavelength λ is NA.
1. Assuming that that of the second optical information recording medium is NA2,
When the wavefront of the condensing optical system is continuous, NA1>
As for the second optical information recording medium satisfying 1.1NA2, it is necessary for reproduction by setting 0.03λ <WSA (NA2) <0.12λWSA (1.1NA2) / WSA (NA2)> 1.2. A spot with a small size of side lobe can be obtained. Here, WSA (NA2) <
When it is 0.03λ, the beam spot is too narrow.
When WSA (NA2)> 0.12λ, the side lobe becomes large and the jitter deteriorates. Also, WSA
When (1.1NA2) / WSA (NA2) <1.2, the spot is too small.

An embodiment according to the present invention will be described below. The symbols used in the embodiments are those described in the comparison of the above-mentioned conventional optical system, and the description is omitted.

(Embodiment 1) Embodiment 1 is the first, second, and third aspects of the present invention.
Tables 4 and 5 show optical data. In the table, di corresponds to the first optical information recording medium, and d
i ′ corresponds to the second optical information recording medium, and di ″ corresponds to the third optical information recording medium.

[0062]

[Table 4]

[0063]

[Table 5]

FIG. 7 shows spherical aberration diagrams of DVD, CD and MO, and FIG. 8 shows the results of CD spot simulation at a defocus position where the best spot shape is obtained. FIG. 9 shows the results of MO spot simulation at the defocus position where the best spot shape is obtained. The results of DVD spot simulation are the same as those shown in FIG.

For DVD, r1 = 0.44 μm,
α1 = 1.8% For CD, r1 = 0.7 μm, for α1 = 5.7% MO, r1 = 0.51 μm, α1 = 7.9% For DVD, CD, MO, By changing the magnification of the objective lens and generating an appropriate spherical aberration, the required numerical aperture on the optical information recording side of the objective lens for obtaining a light spot from which information can be read at the wavelength λ is different, or A good spot can be obtained even when the thickness of the transparent substrate is different. Further, in this embodiment, excessive spherical aberration remains for CD and MO. At this time, since there is little difference between the respective magnifications, there is little change in performance such as a sine condition.

FIG. 10 shows a configuration of an optical pickup device corresponding to the first optical information recording medium of DVD. In the figure, a light beam emitted from a laser light source 1 passes through a hologram beam splitter 2, passes through a lens 3 held by a frame 20 movable in the optical axis direction, becomes a substantially parallel light beam, and is converted into a predetermined light beam by a stop 5. The light is restricted and enters the objective lens 6. The light beam incident on the objective lens 6 is condensed by the objective lens 6 and condensed on the recording surface 8 through the substrate 7. The light beam modulated and reflected by the information pits on the recording surface 8 returns to the hologram beam splitter 2 via the objective lens 6 and the lens 3, where it is separated from the optical path of the laser light source 1, and the light detector serving as a light receiving means 9 is incident. The photodetector 9 is constituted by a multi-divided PIN photodiode, outputs a current proportional to the intensity of the incident light beam from each element, and sends this current to a detection circuit system (not shown) to transmit information. A signal, a focus error signal, and a track error signal are generated. On the basis of the focus error signal and the track error signal, a two-dimensional actuator (not shown) composed of a magnetic circuit and a coil controls an objective lens 6 and an aperture 5 indicated by a dotted line, which are provided integrally, and is constantly controlled. It is configured to position the light spot on the information track.

Next, FIG. 11 shows a configuration of an optical pickup device corresponding to the second optical information recording medium of CD.
In the figure, when reading a thicker second optical information recording medium, the lens 3 is moved by a lens moving means 21 which is a divergence changing means.
Is moved to a predetermined position on the laser light source side in the optical axis direction. Similarly, the same applies to reading of the optical information recording medium of the third MD.

(Embodiment 2) Next, Embodiment 2 is the fourth embodiment.
Table 6 and Table 7 show optical data corresponding to No. 5.
In the table, di and ni represent the first optical information recording medium (DV
D ′ and ni ′ correspond to the second optical information recording medium (CD).

[0069]

[Table 6]

[0070]

[Table 7]

FIG. 12 shows spherical aberration diagrams of DVD and CD, and FIG. 13 shows the results of spot simulation of CD at the defocus position where the best spot shape is obtained. Note that the results of the DVD spot simulation are the same as in FIG.

For DVD, r1 = 0.44 μm,
α1 = 1.8% For CD, r1 = 0.69 μm, α1 = 3.4% For DVD and CD, optical information of the objective lens from which information can be read by making the magnification of the objective lens different for the two light fluxes A good spot can be obtained even when the required numerical aperture on the recording medium side is different or the thickness of the transparent substrate is different. In this embodiment, an excessive spherical aberration is left for the CD.
Similarly to the relationship described above, an under spherical aberration may remain.

Next, FIG. 14 shows a configuration of an optical pickup device corresponding to the first optical information recording medium of DVD. In the figure, a light beam emitted from a laser light source 1 passes through a hologram beam splitter 2, passes through a lens 3, becomes almost a parallel light beam, is restricted to a predetermined light beam by a stop 5, and enters an objective lens 6. The light beam incident on the objective lens 6 is condensed by the objective lens 6 and condensed on the recording surface 8 through the substrate 7. The light beam modulated and reflected by the information pits on the recording surface 8 returns to the hologram beam splitter 2 via the objective lens 6 and the lens 3, where it is separated from the optical path of the laser light source 1, and the light detector serving as a light receiving means 9 is incident. The photodetector 9 is constituted by a multi-divided PIN photodiode, outputs a current proportional to the intensity of the incident light beam from each element, and sends this current to a detection circuit system (not shown) to transmit information. A signal, a focus error signal, and a track error signal are generated. On the basis of the focus error signal and the track error signal, a two-dimensional actuator (not shown) composed of a magnetic circuit and a coil controls an objective lens 6 and an aperture 5 indicated by a dotted line, which are provided integrally, and is constantly controlled. It is configured to position the light spot on the information track.

Next, FIG. 15 shows a configuration of an optical pickup device corresponding to a second optical information recording medium of a CD. In the figure, when reading the optical information recording medium, the turret 34 as the second hologram laser unit switching means is used.
Is rotated around the shaft 35 for switching. When switched, the laser light source 31, the hologram beam splitter 32, and the photodetector 33 as the light receiving means are set.

A hologram laser unit including a laser light source 31, a hologram beam splitter 32, and a photodetector 33, and a mechanism for inserting the laser light source 1, the hologram beam splitter 2, and the photodetector 9 may be used. Also,
The present invention is also applicable to various optical pickup devices described in JP-A-8-55363.

In the first and second embodiments, “Inte
rnational symposium on op
physical memory and optical
No. O for "Data storage 1996"
In the optical path from the laser light source to the photodetector via the information recording surface, as shown in Japanese Patent Application No. 7-330439, the objective lens shown in FIG. As shown in the figure of the mask having the ring-shaped light beam shielding portion, by providing a lens-shaped light beam shielding portion that blocks a light beam incident on the photodetector through a range larger than NA2 and smaller than NA1, furthermore, Good spots can be obtained. If the outer diameter of the light beam shielding portion is too large, the loss of light amount increases, which leads to deterioration in information reading performance from an optical disk for reading with NA1.
Therefore, the shielding of the light beam as a noise component is preferably minimized. Specifically, from the focal position where the best wavefront aberration is obtained in the range of NA2 to the light beam which is focused one to two times behind the focal depth. Is preferably cut.

The same effect can be obtained by a lens having a step described in Japanese Patent Application No. 8-123375. The photodetector has an element configuration of an eight-division photodetector shown in FIG. 17 in which a portion that can receive a light beam passing through the range of NA2 and a portion that can receive a light beam that passes between NA1 and NA2 are divided. By using such a photodetector, a better signal can be obtained.

FIG. 17 is a diagram showing an element configuration of an 8-part photodetector, and FIG. 17A is a diagram showing the configuration of the element.
FIG. 17B is a diagram showing a state of condensing a light beam from the first optical disk having a transparent substrate thickness t = 0.6 mm, and FIG. 17C is a second optical disk having a transparent substrate thickness t = 1.2 mm. It is a figure which shows the condensing state of the light beam from. In the drawing, the dividing line S is made to substantially coincide with the mapping of the information track on the information recording surface of the optical disk, and is divided into an inner quadrant and an outer quadrant by the dividing line R. Is done.
In FIG. 17B, more specifically, the thickness t =
This shows a state in which a light beam from a 0.6 mm first optical disc is condensed on an eight-segment photodetector with a spot diameter.

The focus error signal is obtained by the astigmatism method as (A1 + A2 + C1 + C2)-(B1 + B2 + D1 + D
2) The track error signal is obtained by the push-pull method (A1 + A2 + B1 + B2)-(C1 + C2 + D1 + D
2) Detected in.

The information signal is the sum of all elements (A1 + A2 + B1 + B2 + C1 + C2 + D1 + D
2) or (A2 + B2 + C2 + D)
It is detected in 2). If signal detection is performed only from the outer peripheral portion, the high frequency component is emphasized, and the modulation degree of the shortest pit can be improved.

Next, referring to FIG. 17C, the thickness t of the transparent substrate
This shows a state in which a light beam from the second optical disc of = 1.2 mm is condensed on an eight-segment photodetector with a spot diameter. It has a high light intensity at the center and the outer side becomes a flared condensate, and mainly receives light at this center (A1 + B1
+ C1 + D1) to detect an information signal. This light receiving range is desirably the NA2.

The focus error signal is obtained by the astigmatism method by (A1 + A2 + C1 + C2)-(B1 + B2 + D1 + D
2) or (A1 + C1)-(B1 + D1) The track error signal is obtained by the push-pull method (A1 + A2 + B1 + B2)-(C1 + C2 + D1 + D)
2) or (A1 + B1)-(C1 + D1).

As described above, by dividing the photodetector in the area where the information signal is detected, it is possible to detect the signal in an area where there is no flare light due to spherical aberration, and the reproduction performance is improved. Further, by providing the ring-shaped light beam shielding portion in the optical path, the light beam which becomes a noise component can be further cut to reduce jitter.

Here, it is assumed that NA1> 1.1NA2, but it is desirable that NA1> 1.2NA2 to obtain more effects.

(Embodiment 3) Embodiment 3 corresponds to claims 6 and 7, and FIG. 18 is an optical axis sectional view of an objective single lens having a substantial stop. In the figure, the effective radius H1 of the objective single lens (also referred to as the objective lens) 6 indicates the radius of the objective lens, and the lens surface 61 larger than the effective radius H1 is transparent, and the light that plays the role of a substantial diaphragm is It is the part that passes.

The objective single lens 6 can function as a stop by making the light outside the effective radius H1 significantly different from the position where the light within the effective radius converges. Within the effective diameter, the ray aberration is 4λ
/ (NA) ^{2 or} less. When used without an aperture, 1.02 NA only needs to have a large ray aberration.

Normally, considering the third order spherical aberration, since it is proportional to the fourth power of NA, if the numerical aperture NA is 4λ /
(NA) if ² of the aberration, the ray aberration of approximately 4.3λ / (NA) ^2. If the ray aberration is significantly larger than this,
Even if there is no stop, it will function as a lens with a numerical aperture of NA. There is no problem if the amount is about twice or more the above amount. That is, 8λ / 1.02NA
(NA) It is sufficient to have ² ray aberrations. The conditions for the stop are as described above. However, the setting is made so that a light beam that is not actually restricted by the stop causes a flare to adversely affect a reproduced signal or cause a safety problem. In addition, as a guideline for the wavefront aberration, WSA (H1) <0.05λ SA (1.02H1) / WSA (H1)> 1.2 Such a substantial stop integrated with the lens is not suitable. In the processing of the spherical mold, it can be processed at the same time,
Both the concentricity and the position accuracy are better than those provided separately.

[0088]

According to the configuration described above, the following effects can be obtained. Using a single objective lens, the present invention can be realized without complicating pickup devices for various optical disks having different substrate thicknesses and recording densities. Also, due to problems such as reflectance,
When the laser wavelength to be used is limited, an extremely simple optical system can be realized even if it is unavoidable to use a plurality of laser light sources. In particular, an optical system that does not require the insertion of an aperture stop or an aperture stop adjustment device, and that does not make it difficult to reproduce a CD with a large eccentricity due to a decrease in tracking range due to the shaking by the fixed stop. In addition, a simple structure is obtained by omitting the aperture provided on the light source side of the objective lens.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a conventional optical pickup device.

FIG. 2 is a diagram of a spot simulation of an aberration-free optical system.

FIG. 3 is a spherical aberration diagram of a DVD and a CD.

FIG. 4 is a DVD spot simulation at a defocus position where the best spot shape is obtained.

FIG. 5 is a CD spot simulation at a defocus position where the best spot shape is obtained.

FIG. 6 is a spot simulation of a CD.

FIG. 7 is a spherical aberration diagram of DVD, CD, and MO.

FIG. 8 is a CD spot simulation at a defocus position where the best spot shape is obtained.

FIG. 9 shows an MO spot simulation at a defocus position where the best spot shape is obtained.

FIG. 10 is a configuration diagram of an optical pickup device corresponding to a first optical information recording medium of DVD.

FIG. 11 is a configuration diagram of an optical pickup device corresponding to a second optical information recording medium of a CD.

FIG. 12 is a spherical aberration diagram of a DVD and a CD.

FIG. 13 is a CD spot simulation at a defocus position where the best spot shape is obtained.

FIG. 14 is a configuration diagram of an optical pickup device corresponding to a first optical information recording medium of DVD.

FIG. 15 is a configuration diagram of an optical pickup device corresponding to a second optical information recording medium of a CD.

FIG. 16 is a view of a mask having a ring-shaped light beam shielding portion.

FIG. 17 is a diagram illustrating an element configuration of an 8-part photodetector.

FIG. 18 is a sectional view along the optical axis of an objective single lens having a substantial stop.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Laser light source 2 Beam splitter (hologram beam splitter) 3 Lens 5 Aperture 6,11 Objective lens (Objective single lens) 7 Substrate 8 Recording surface (information recording surface) 9 Photodetector (light receiving means) 10 Aperture 20 Frame 21 Lens movement Means 31 Laser light source 32 Beam splitter 33 Photodetector (light receiving means) 34 Turret 35 Axis S, R division line

Claims (13)

[Claims] 1. A laser light source, an objective lens having a positive refractive power for condensing a light beam from the laser light source on an information recording surface of an optical information recording medium, and reflected by the information recording surface and passing through the objective lens An optical pickup device for an optical information recording medium having a light receiving means for receiving the light beam thus converted and a divergence changing means for changing the divergence of the light beam incident on the objective lens, wherein the wavelength of the laser light source is λ and the light is incident on the information recording surface. Regarding the light beam, when the spherical aberration component of the wavefront aberration RMS value of the light beam having a numerical aperture NA or less is represented by WSA (NA), the light spot from which information can be read for the first optical information recording medium has a wavelength λ.
When the required numerical aperture of the objective lens on the side of the optical information recording medium to obtain in step (1) is NA1, for the first optical information recording medium, the numerical aperture of the light beam emitted from the objective lens is NA1, and WSA (NA1) <0.05λ Further, the required numerical aperture of the objective lens on the side of the optical information recording medium of the objective lens for obtaining a light spot at which the information can be read from the second optical information recording medium at the wavelength λ is NA2. In the case of the first optical information recording medium, the divergence of the light beam incident on the objective lens is changed by the divergence degree changing means so as to satisfy the following condition for the second optical information recording medium. An optical pickup device characterized by being different from the above. NA1> 1.1NA2 0.03λ <WSA (NA2) <0.12λ WSA (1.1NA2) / WSA (NA2)> 1.2 2. A laser light source; an objective lens having a positive refractive power for condensing a light beam from the laser light source onto an information recording surface via a transparent substrate of an optical information recording medium; An optical pickup device for an optical information recording medium, comprising: a light receiving unit that receives a light beam that has passed through the objective lens; and a divergence changing unit that changes a divergence of the light beam incident on the objective lens. When the spherical aberration component of the wavefront aberration RMS value of a light beam having a numerical aperture NA or less passing through a transparent substrate is defined as WSA (NA) with respect to the light beam emitted from the lens, information is read from the first optical information recording medium. When the required numerical aperture on the optical information recording medium side of the objective lens for obtaining an output light spot at the wavelength λ is NA1, the objective lens is emitted to the first optical information recording medium. The numerical aperture of the light beam is NA1 and the following condition is satisfied: WSA (NA1) <0.05λ Further, information on a second optical information recording medium having a transparent substrate thickness different from that of the first optical information recording medium is described. Assuming that the required numerical aperture of the objective lens on the optical information recording medium side for obtaining a readable optical spot at the wavelength λ is NA2, the second optical information recording medium satisfies the following condition. An optical pickup device wherein the divergence changing means makes the divergence of a light beam incident on an objective lens different from that of the first optical information recording medium. NA1> 1.1NA2 0.03λ <WSA (NA2) <0.12λ WSA (1.1NA2) / WSA (NA2)> 1.2 3. A laser light source, an objective lens having a positive refractive power for condensing a light beam from the laser light source on a information recording surface via a transparent substrate of an optical information recording medium, and reflected by the information recording surface. An optical pickup device for an optical information recording medium, comprising: a light receiving unit that receives a light beam that has passed through the objective lens; and a divergence changing unit that changes a divergence of the light beam incident on the objective lens. When the spherical aberration component of the wavefront aberration RMS value of a light beam having a numerical aperture NA or less passing through a transparent substrate with respect to a light beam emitted from a lens is defined as WSA (NA), information is read from the first optical information recording medium. When the required numerical aperture on the optical information recording medium side of the objective lens for obtaining an output light spot at the wavelength λ is NA1, the objective lens is emitted to the first optical information recording medium. The numerical aperture of the light flux is NA1, and the light from the objective lens for obtaining a light spot at a wavelength λ from which information can be read out on a second optical information recording medium having a transparent substrate different in thickness from the first optical information recording medium. When the required numerical aperture on the information recording medium side is NA2, NA1> 1.1NA2, and for the second optical information recording medium, an optimal light spot for reading recorded information is obtained. An optical pickup device wherein the divergence of the light beam incident on the objective lens is made different from that of the first optical information recording medium by the divergence changing means. 4. A first laser light source, a second laser light source, an objective lens having a positive refractive power for condensing a light beam from the laser light source on an information recording surface of an optical information recording medium, An optical pickup device for an optical information recording medium having light receiving means for receiving a light beam reflected by the information recording surface and passing through the objective lens, wherein the wavelength of the first laser light source is λ1, and the light beam incident on the information recording surface is: Wavefront aberration RMS of light beam with numerical aperture NA or less
When the spherical aberration component of the value is WSA (NA), the first
When the required numerical aperture on the optical information recording medium side of the objective lens for obtaining an optical spot at which the information can be read from the optical information recording medium at wavelength λ1 is set to NA1, the first optical information recording medium is The numerical aperture of the light beam emitted from the objective lens is N
A1 satisfies the following condition: WSA (NA1) <0.05λ1 Furthermore, an objective lens on the optical information recording medium side of the objective lens for obtaining a light spot at wavelength λ2 from which information can be read for the second optical information recording medium. When the required numerical aperture is NA2, NA1> 1.1NA2, and the divergence of the second light flux incident on the objective lens for the second optical information recording medium so as to satisfy the following condition. And a divergence of the first light flux. 0.03λ <WSA (NA2) <0.12λ2 WSA (1.1NA2) / WSA (NA2)> 1.2 5. A first laser light source, a second laser light source, an objective lens having a positive refractive power for condensing a light beam from the laser light source on an information recording surface of an optical information recording medium, A light receiving means for receiving a light beam reflected by the information recording surface and passing through the objective lens, wherein the wavelength of the first laser light source is λ1, the information about the first optical information recording medium is The required numerical aperture of the objective lens on the optical information recording medium side to obtain a light spot at
When the number is 1, the first optical information recording medium uses the first light beam, the numerical aperture of the light beam emitted from the objective lens is NA1, and the information on the second optical information recording medium is When the required numerical aperture on the optical information recording medium side of the objective lens for obtaining a light spot at which the wavelength can be read at the wavelength λ2 is NA2, NA1> 1.1NA2, and for the second optical information recording medium, , The divergence of the light beam incident on the objective lens is made different from that of the first light beam in order to obtain an optimum light spot for reading recorded information using the second light beam. Optical pickup device. 6. A laser light source, an objective single lens having a positive refractive power for condensing a substantially aberration-free light beam from the laser light source onto an information recording surface via a transparent substrate of an optical information recording medium, and The wavelength of the laser light source is λ in the objective single lens for recording / reproducing of the optical information recording medium of the optical pickup device of the optical information recording medium having the light receiving means for receiving the light beam reflected by the recording surface and passing through the objective single lens, The required numerical aperture of the objective single lens on the optical information recording medium side for obtaining a light spot at which the information can be read from the recording medium at the wavelength λ is N
Numerical aperture NA emitted from the objective single lens when A1
Assuming that the effective radius of the light source side surface of the light beam 1 is H1,
At least the light beam incident on the range from H1 to 1.02H1 transmits the objective single lens and converts the spherical aberration component of the wavefront aberration RMS value of the light beam having an incident height H or less incident on the objective lens through the transparent substrate. An objective single lens for recording / reproducing an optical information recording medium, wherein the objective lens has WSA (H) and satisfies the following conditions. WSA (H1) <0.05λ WSA (1.02H1) / WSA (H1)> 1.2 7. A laser light source, an objective single lens having a positive refractive power for condensing a substantially aberration-free light beam from the laser light source onto an information recording surface via a transparent substrate of an optical information recording medium, and In a recording / reproducing objective single lens of an optical information recording medium of an optical pickup device for an optical information recording medium having light receiving means for receiving a light beam reflected by a recording surface and passing through the objective lens, the wavelength of the laser light source is λ, the optical information is Assuming that the required numerical aperture on the optical information recording medium side of the objective single lens for obtaining a light spot from the recording medium at which the information can be read at the wavelength λ is NA1, the light source side of the light beam of the numerical aperture NA1 emitted from the objective single lens. When the effective radius of the surface is H1, at least H1
The light flux incident on the lens from 1.0 to 1.02H1 passes through the objective single lens and satisfies the following condition when the vertical spherical aberration at the incident height H incident on the objective lens is SA (H). An objective single lens for recording / reproducing an optical information recording medium, characterized in that: | SA (1.02H1) |> 8λ / (NA1) ² 8. A ring-shaped light path for blocking a light beam passing through a range larger than NA2 and smaller than NA1 from entering the photodetector in an optical path from the laser light source to the photodetector via the information recording surface. The optical pickup device according to any one of claims 1 to 5, further comprising a light beam shielding unit. 9. A ring shape on the surface of the objective lens on the side of the laser light source or on the side of the optical information recording medium, for blocking a light beam passing through a range larger than NA2 and smaller than NA1 from entering the photodetector. The optical pickup device according to any one of claims 1 to 5, further comprising: a light flux shielding portion. 10. The photodetector includes a plurality of light receiving elements in which a portion capable of receiving a light beam passing through the range of NA2 and a portion capable of receiving a light beam passing between NA1 and NA2 are divided. The optical pickup device according to any one of claims 1 to 5, wherein: 11. A light beam emitted from a laser light source is focused as a light spot on an information recording surface of an optical information recording medium by a focusing optical system, and reflected light from the information recording surface is received by a photodetector. An information reproducing method for reproducing information recorded on an information recording surface of the optical information recording medium, wherein a wavelength of a light beam emitted from the laser light source is λ, and a light beam incident on the information recording surface has a numerical aperture NA or less. Assuming that the spherical aberration component of the wavefront aberration RMS value of the light flux is WSA (NA), the condensing optical system must satisfy the condition of WSA (NA1) <0.05λ in the range of the numerical aperture NA1 on the information recording surface side. When a condensing optical system capable of obtaining a satisfactory first light spot is used and information is reproduced by a second light spot having a larger diameter than the first light spot, spherical aberration is reduced. Raise Information reproducing method characterized by reproducing information to obtain the second light spot by. 12. A light beam emitted from a laser light source is condensed as a light spot on an information recording surface of an optical information recording medium by a condensing optical system, and reflected light from the information recording surface is received by a photodetector. An information reproducing method for reproducing information recorded on an information recording surface of the optical information recording medium, wherein a wavelength of a light beam emitted from the laser light source is λ, and a light beam incident on the information recording surface has a numerical aperture NA or less. Assuming that the spherical aberration component of the wavefront aberration RMS value of the light flux is WSA (NA), the condensing optical system must satisfy the condition of WSA (NA1) <0.05λ in the range of the numerical aperture NA1 on the information recording surface side. When information is reproduced by a second light spot having a diameter larger than that of the first light spot, using a condensing optical system capable of obtaining a satisfactory first light spot, the second light spot Light spot NA1> 1.1NA2 0.03λ <WSA (NA2) <0.12λ WSA (1.1NA2) / WSA An information reproducing method characterized in that information is reproduced by generating a spherical aberration that satisfies a condition of (NA2)> 1.2. 13. The focusing optical system according to claim 11, wherein the condensing optical system has at least an objective lens, and generates a spherical aberration by changing a divergence of a light beam incident on the objective lens. Information reproduction method.