JPH1069675A - Optical pickup device, objective lens of optical pickup and optical disk device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a compact optical pickup device capable of reproducing the optical disk having different substrate thickness with one optical pickup device and having mutual compatibility and a simple structure. SOLUTION: In this optical pickup device, the luminous flux from a laser beam source 1 is condensed on a recording surface 8 via the transparent substrate 7 of an optical disk and reproduced by receiving the reflecting light from the recording surface 8 with a light detector 9. In this case, when the number of the aperture in the optical disk side of an optical system required for obtaining a light spot reading information of a first optical disk having the thickness t1 of the substrate 7 and the recording density i1 with a wavelength λ is meant by NA1, and the number of the aperture in the optical disk side of the optical system required for obtaining the light spot reading information of a second optical disk having the thickness t2 of the substrate and the recording density i2 with the wavelength λ is meant by NA2, it is specified that the number NA2 of the aperture in the optical disk side of the optical system is >=NA1, the best wave front aberration of the light spot by the substrate of thickness t1 is <0.05λrms, and the best wave front aberration of the light spot by the substrate of thickness t2 is <0.07λrms within the range of NA2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pickup device for an optical information recording medium for reproducing optical information by irradiating an optical information recording medium with a light beam such as a laser beam, an objective lens for the optical pickup, and an optical disk device. About.

[0002]

2. Description of the Related Art A conventional technique according to the present invention will be described.

In the following description, an optical disc will be described as an example of an optical information recording medium.

In recent years, short wavelength red semiconductor lasers (λ = 63
With the practical use of the optical disc (5 to 690 nm), the development of a DVD (digital video disc) having an optical disc size similar to that of a conventional CD (compact disc) and a larger capacity has been progressing. In this DVD system optical disk, the NA of the objective lens of the optical pickup is set to 0.
6. The thickness of the disc substrate is 0.6 mm, which is half that of the conventional CD.
And The track pitch is 0.74 μm, the shortest pit length is 0.4 μm, and the CD track pitch is 1.6 μm.
The density is reduced to less than half of the shortest pit length of 0.86 μm.

[0005] An optical disk device capable of reproducing such a DVD, which can also reproduce a conventional CD, is required for utilizing software assets.

FIG. 1 is a diagram of an optical pickup device used in an optical disk device that has been conventionally considered.

In FIG. 1, a light beam emitted from a laser light source 1 passes through a hologram beam splitter 2, enters a collimator lens 3, becomes a parallel light beam, is limited to a predetermined light beam by a stop 5, and enters an objective lens 6. The objective lens 6 forms an aberration-free light spot on the information recording surface 8 through a substrate 7 having a certain thickness (here, t = 0.6 mm) when a parallel light beam enters.

The light flux 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 collimator lens 3, where it is separated from the optical path from the laser light source 1. Detector 9
Incident on. This 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 this current to a detection circuit system (not shown) where the information signal is output. , A focus error signal and a track error signal. The objective lens 6 is controlled in a focusing direction and a tracking direction by a two-dimensional actuator (not shown) composed of a magnetic circuit and a coil based on the focus error signal and the track error signal, so that the light spot position is always on the information track. Match.

In such an optical pickup device, a large NA is used to reduce the light spot condensed by the objective lens 6.
(For example, NA 0.6), a large spherical aberration is generated when the thickness of the substrate 7 placed in such a converged light beam deviates from a predetermined thickness.

FIG. 2 is a diagram showing the relationship between the substrate thickness and the best wavefront aberration.

Referring to FIG. 2, the objective lens is optimized under the conditions of NA of 0.6, wavelength of laser light emitted from a laser light source of 635 nm, substrate thickness of 0.6 mm, and substrate refractive index of 1.58. If you change the thickness of
The aberration increases by about 0.01 λrms for every mm displacement.
If the substrate thickness is shifted by ± 0.07 mm, the aberration becomes 0.07 λrms, and reaches the Marechal's limit value which is a standard for performing normal reading.

Therefore, for example, when an optical disk having a substrate of 1.2 mm thickness is to be reproduced instead of an optical disk having a substrate of 0.6 mm thickness, 1.
An objective lens 61 and an aperture 51 designed to obtain an aberration-free light spot through a 2 mm-thick substrate are switched for reproduction.

Alternatively, for a substrate having a thickness of 0.6 mm and 1.2 mm
A method of mounting two optical pickup devices for a thick substrate in one optical disk device has also been considered.

Also, a hologram is provided in the optical pickup device, and each of the 0th-order light and the 1st-order light passing through the hologram is 0.6 mm.
A method of converging light spots on an information recording surface as light spots corresponding to a mm-thick substrate and a 1.2-mm-thick substrate has also been considered.

[0015]

As described above, in order to make an optical disk apparatus capable of reproducing optical disks having different substrate thicknesses by one optical disk apparatus, for example, one optical pickup apparatus has a structure in which the optical disk substrate thickness is zero. For 6mm and 1.
Attach two objective lenses each corresponding to 2 mm, or set the optical disc substrate thickness to 0.6 m
In the method using two optical pickup devices for m and 1.2 mm, the optical pickup device and the optical disk device cannot be made compact and low in cost.

A hologram is provided in the optical path of the condensing optical system of the optical pickup device, and the 0th-order light and the 1st-order light passing through the hologram are formed as light spots corresponding to a 0.6 mm thick substrate and a 1.2 mm thick substrate. In the method of converging an information recording surface with an objective lens, two light beams are always emitted toward the information recording surface of the optical disk. Therefore, when information is read at a light spot using one light beam, the other light beam is read. Becomes unnecessary light that does not contribute, and becomes a factor of increasing noise. In addition, since the laser light intensity is divided and used, the S / N ratio decreases due to the decrease in the amount of light returning to the photodetector. The life will be shortened. Further, when the recording method is adopted, a higher output laser is required due to an increase in the emission loss, which increases the cost.

The present invention has been made to solve the above problems. That is, an optical pickup device can reproduce optical disks having different substrate thicknesses,
It is an object of the present invention to provide an optical pickup device having a simple structure and a compact size, an objective lens of the optical pickup, and an optical disk device.

[0018]

The object of the present invention is achieved by adopting the following constitution.

(1) The light beam emitted from the laser light source is
An optical pickup device that condenses light as a light spot on an information recording surface via a transparent substrate of an optical information recording medium by a condensing optical system, receives light reflected from the information recording surface with a photodetector, and reproduces information. , The necessary numerical aperture on the optical information recording medium side of the optical information recording medium side of the condensing optical system for obtaining, at the wavelength λ, a light spot from the first optical information recording medium having a transparent substrate thickness t1 and information recording density i1. The necessary numerical aperture on the optical information recording medium side of the converging optical system for obtaining a light spot at wavelength λ from which information of the second optical information recording medium having the thickness t2 of the transparent substrate and the information recording density i2 can be read is defined as NA2. When the numerical aperture NA0 of the condensing optical system on the side of the optical information recording medium is NA1 or more, the best wavefront aberration of the light spot when passing through the transparent substrate having the thickness t1 is 0.05λrms or less, and t2 transparent group The best wavefront aberration of the light spot when the via is an optical pickup apparatus is characterized in that the 0.07λrms less within the range of NA2. However, t1 <
t2, i1> i2, NA1> NA2, and λ are the wavelengths of the laser light source.

(2) The light beam emitted from the laser light source is
An optical pickup device that condenses light as a light spot on an information recording surface via a transparent substrate of an optical information recording medium by a condensing optical system, receives light reflected from the information recording surface with a photodetector, and reproduces information. , The necessary numerical aperture on the optical information recording medium side of the optical information recording medium side of the condensing optical system for obtaining, at the wavelength λ, a light spot from the first optical information recording medium having a transparent substrate thickness t1 and information recording density i1. The necessary numerical aperture on the optical information recording medium side of the converging optical system for obtaining a light spot at wavelength λ from which information of the second optical information recording medium having the thickness t2 of the transparent substrate and the information recording density i2 can be read is defined as NA2. When the numerical aperture NA0 of the condensing optical system on the optical information recording medium side is NA1 or more, the best wavefront aberration of the light spot when passing through the transparent substrate having the thickness t1 is 0.05λrms or less, and the laser light source Condensed light from In the optical path up toward the optical detector through the system, the optical pickup apparatus characterized in that a NA1 is smaller than the ring-shaped light flux shielding portion greater than NA2. Where t1 <t2, i1> i2, NA1> NA2,
λ is the wavelength of the laser light source.

(3) The light beam emitted from the laser light source is
An optical pickup device that condenses light as a light spot on an information recording surface via a transparent substrate of an optical information recording medium by a condensing optical system, receives light reflected from the information recording surface with a photodetector, and reproduces information. , The necessary numerical aperture on the optical information recording medium side of the optical information recording medium side of the condensing optical system for obtaining, at the wavelength λ, a light spot from the first optical information recording medium having a transparent substrate thickness t1 and information recording density i1. The necessary numerical aperture on the optical information recording medium side of the converging optical system for obtaining a light spot at wavelength λ from which information of the second optical information recording medium having the thickness t2 of the transparent substrate and the information recording density i2 can be read is defined as NA2. When the numerical aperture NA0 of the condensing optical system on the side of the optical information recording medium is NA1 or more, the best wavefront aberration of the light spot when passing through the transparent substrate having the thickness t1 is 0.05λrms or less. Multiple detectors Is divided into band, first, the optical pickup apparatus characterized by having different areas for reproducing an information signal in the second optical information recording medium. However, t1 <t2,
i1> i2, NA1> NA2, λ is the wavelength of the laser light source.

(4) The optical pickup device according to (3), wherein the area of the photodetector for reproducing the information signal of the second optical information recording medium is an area corresponding to the range of NA2.

(5) On the optical path from the laser light source to the photodetector via the condensing optical system, a ring-shaped light beam shielding portion larger than NA2 and smaller than NA1 is provided (3). Or the optical pickup device according to (4).

(6) Regarding the spherical aberration of the condensing optical system when the light passes through the transparent substrate having the thickness t1, the (1/2) NA2 light beam is overcorrected (overcorrected) than the NA2 light beam. The optical pickup device according to any one of the above (1) to (5). However, (1/2) NA2 is NA
It shall represent 1/2 of 2.

(7) The thickness t1 of the transparent substrate is 0.6 m
m, the numerical aperture NA0 is λ (μm) /1.14 (μm) or more, the thickness t2 of the transparent substrate is 1.2 mm, and the numerical aperture NA is
2 is λ (μm) /1.75 (μm) or λ (μm)
/2.46 (μm)
The optical pickup device according to any one of (6).

(8) A light beam from a laser light source is condensed as a light spot on the information recording surface of an optical information recording medium via a transparent substrate, and light for reading information recorded on the information recording surface is read. In the objective lens of the pickup, the required numerical aperture on the optical information recording medium side of the objective lens for obtaining, at a wavelength λ, an optical spot from which information on the first optical information recording medium can be read with a thickness t1 of the transparent substrate and an information recording density i1. Is the required numerical aperture on the optical information recording medium side of the objective lens for obtaining a light spot at a wavelength λ from which information of the second optical information recording medium can be read with NA1 and the thickness t2 of the transparent substrate and the information recording density i2.
When the objective lens of the optical pickup has the best wavefront aberration of 0.05 when passing through the transparent substrate having the thickness t1,
λrms or less, and (１ ／) NA from the luminous flux of NA2
2. The objective of the optical pickup, wherein the light beam of No. 2 has overcorrected spherical aberration, and a ring-shaped light beam shielding portion is provided on an entrance surface or an exit surface of a region larger than NA2 and smaller than NA1. lens. However, t1 <t
2, i1> i2, NA1> NA2, [lambda] are the wavelengths of the laser light source, and (1/2) NA2 represents 1/2 of NA2.

(9) The light beam emitted from the laser light source is condensed as a light spot on the information recording surface through the transparent substrate of the optical information recording medium by the light condensing optical system, and the reflected light from the information recording surface is converted to light. In an optical pickup device for receiving information from a detector and reproducing information, the optical information recording medium of the condensing optical system necessary for reproducing information of the optical information recording medium having a thickness of the transparent substrate of t1 with light having a wavelength of λ. The numerical aperture on the side of the optical information recording medium of the condensing optical system necessary for reproducing the information of the optical information recording medium at t2 in which the thickness of the transparent substrate is greater than t1 with light of the wavelength λ. The numerical aperture of NA2 (<N
A1) When the numerical aperture on the optical information recording medium side of the condensing optical system that is larger than NA2 and smaller than NA1 is NA3, the numerical aperture NA on the optical information recording medium side of the condensing optical system.
0 is the NA1 or more, and the best wavefront aberration of the light spot through the transparent substrate having the thickness t1 is 0.0
7λrms or less, of the reflected light reaching the photodetector after being reflected by the information recording surface of the optical information recording medium, the NA3 to NA2 of the lens surface of the condensing optical system closest to the optical information recording medium. A light beam shielding unit that shields at least a part of a ring-shaped light beam that passes through a range and reaches the photodetector is provided in an optical path between an optical information recording medium and the photodetector. Optical pickup device.

(10) The optical pickup device according to (9), wherein the light-shielding portion is formed on a surface of the objective lens of the focusing optical system on the side of the laser light source.

(11) The NA2 is λ (μm) / 1.
(9) or (1)
The optical pickup device according to 0).

(12) The NA2 is λ (μm) / 2.
(9) or (1)
The optical pickup device according to 0).

(13) The NA3 is 1.1NA2-
(9)-(12), characterized by being 1.2NA2.
The optical pickup device according to claim 1.

(14) An optical pickup device, an objective lens of the optical pickup, or a condensing optical system of the optical pickup according to any one of (1) to (13), and light having a thickness of t2 of the transparent substrate. When reproducing the information of the information recording medium with light having a wavelength of λ, the apparatus has focusing control means for performing focusing control so that the objective lens of the condensing optical system is focused farther than the paraxial focus. Optical disk device.

The "best wavefront aberration" in the present invention is a wavefront aberration corrected for a defocus component and a tilt component, and its value is represented by root mean square (rms).

[0034]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention relates to an optical pickup device for reproducing a DVD, for example, when reproducing an optical disk having a 1.2 mm thick substrate such as a conventional CD, using a 780 nm light source for a CD.
The effective NA of the objective lens required for reading is small (0.26 to 0.40), which is shorter than the wavelength of 635 nm to 690 nm, and the light flux within this range is a condensing optical system for DVD reproduction. Reading is performed as it is.

An embodiment of the present invention will be described below.

In each embodiment, in the numerical example of the condensing optical system, the laser light source is set to the 0th surface, the radius of curvature of the i-th surface (including the stop surface) is ri, and the i-th surface The refractive index at the wavelength of the light flux of the laser light source of the medium between the surface and the (i + 1) -th surface is represented by ni. The refractive index of air is 1
And

When an aspherical surface is used for the lens surface, the aspherical shape is such that the X axis is in the optical axis direction, the H axis is perpendicular to the optical axis, the light traveling direction is positive, and r is near. When the radius of curvature of the axis, K is a conic coefficient, Aj is an aspheric coefficient, and Pj is a power of an aspheric surface (where Pj ≧ 3),

[0038]

(Equation 1)

Is represented by

(Embodiment 1) In FIG. 3, a light beam emitted from a laser light source 1 passes through a hologram beam splitter 2, passes through a collimator lens 3, becomes a substantially parallel light beam, and is restricted by a stop 5 to a predetermined light beam. Then, the light enters the objective lens 6. The light beam incident on the objective lens 6 has a thickness of 0.1 mm.
The light is focused on the information recording surface 8 through the 6 mm substrate 7.
The light flux 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 collimator lens 3, where it is separated from the optical path of the laser light source 1 and to the photodetector 9. Incident.

The photodetector 9 is composed of 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 (not shown). Here, an information signal, a focus error signal, and a track error signal are generated. Based on the focus error signal and the track error signal, the objective lens 6 and the aperture 5 provided integrally by a two-dimensional actuator (not shown) composed of a magnetic circuit and a coil are controlled in a focusing direction and a tracking direction. , The light spot position is always adjusted on the information track.

Next, Tables 1 and 2 show optical data of the condensing optical system in the example shown in FIG.

[0043]

[Table 1]

[0044]

[Table 2]

In this example, the light source wavelength is 635 nm and the axial best wavefront aberration is 0.001λrms when NA0 = 0.6.
It is.

The wavefront aberration used as a guide of the diffraction limit is 0.0
If it is within 7λrms and is equal to or less than the diffraction limit, information can be reproduced. It should be noted that, for reproducing a DVD whose information recording density i1 is higher than that of a conventional optical disc such as a CD with respect to the light spot size, it is desirable to set it within 0.05λrms.

FIG. 4 shows the relationship between NA, the best wavefront aberration and the optimum defocus amount when a light spot is condensed through the second substrate thickness t = 1.2 mm with this condensing optical system. FIG.

In FIG. 4, the best wavefront aberration at the full aperture of NA0 = 0.6 is 0.60λrms, and the spot position at this time is 23 μm behind the paraxial focal point in air conversion. The wavefront aberration at this time is mainly a spherical aberration component, and this aberration sharply decreases as the NA decreases. When NA is 0.37, the best wavefront aberration is almost 0.07λrm.
s, which is within Marechal's limits. The spot position at this time is about 8 μm behind the paraxial focal point in air conversion. When the NA is 0.3, the best wavefront aberration is almost 0.
The spot position is about 5 μm behind the paraxial focus in air conversion.

In the case of a CD system using an optical disk having a substrate thickness of 1.2 mm, a sufficient reading performance can be obtained when λ / NA = 1.75 (μm) or more. When λ = 780 nm, NA =
0.45, λ = 648 nm when NA = 0.37,
At NA = 0.30, λ = 525 nm. Therefore, λ
The objective lens is driven by a two-dimensional actuator with respect to the information recording surface by a two-dimensional actuator to perform focusing control so that the laser beam having a wavelength of 635 nm is used and the NA is 0.37 and the paraxial focal point that gives the best wavefront aberration is about 8 μm in air conversion from the paraxial focus. Thereby, information on an optical disk having a substrate thickness of 1.2 mm can be read.

It is also possible to reduce the intersymbol interference by using an equalizer in the signal processing system and make the ratio of the spot size to the information recording density the same as that of the DVD, and further reduce the NA to reproduce the CD optical disk. It is.
NA2 at this time = λ (μm) /2.46 (μm) ≒
0.26, and the best wavefront aberration is sufficiently small at 0.016 λrms.

At this time, NA2 (0.37 or 0.2
6) The luminous flux passing through the area not less than NA0 (0.60) does not contribute to information reading and becomes unnecessary light. The luminous flux in this area has a large spherical aberration and is condensed further behind the information recording surface, and the luminous flux reflected by the information recording surface is further subjected to spherical aberration through the substrate, the objective lens, and the collimator lens. To the photodetector, and becomes flare light on the photodetector. For this reason, the light receiving area of the photodetector is preferably set to have a minimum necessary area so as to cut off the flare light.

(Embodiment 2) FIG. 5 is a view showing an optical pickup device of Embodiment 2 of the present invention.

In FIG. 5, the laser light source 11 (λ = 68
0 nm) from the polarization beam splitter 1
2. The light passes through the collimator lens 13 and the quarter-wave plate 14 to become a circularly polarized parallel light beam. This light flux is condensed on an information recording surface 8 via a substrate 7 of an optical disk by an objective lens 6 driven in a focusing direction and a tracking direction by a two-dimensional actuator (not shown). The light flux modulated and reflected by the information pits on the information recording surface 8 is
Again, the light passes through the objective lens 6, the quarter-wave plate 14, and the collimator lens 13 and is incident on the polarization beam splitter 12,
Here, the light is reflected and travels to the photodetector 19. Astigmatism is given by the cylindrical lens 10 arranged on the optical path to the photodetector 19, and the magnification is enlarged by the concave lens 16.

FIG. 6 is a diagram showing the element configuration of the photodetector.

In FIG. 6, the photodetector 19 is composed of four elements A to D as shown in FIG.
The dividing line S is arranged so that the direction substantially coincides with the mapping of the information track on the information recording surface of the optical disc, and is oriented at approximately 45 ° with respect to the generating line of the cylindrical lens 10. The focus error signal is detected by the astigmatism method, the calculation of (A + C)-(B + D) is performed, and the track error signal is detected by the push-pull method, for example.
By the calculation of (A + B)-(C + D), in the phase difference detection method, it is obtained by the calculation of (A + C)-(B + D), and the information signal is obtained by (A + B + C + D). All of these detection methods are well known, and detailed description is omitted.

Next, Tables 3 and 4 show optical data of the condensing optical system used in the optical pickup device of FIG.

By optimizing the design of the collimator lens 13, it is possible to cause a substantially illuminated parallel light beam to be incident on the objective lens. Assuming that a collimator lens is used, the configuration after the light beam enters the objective lens will be described. In this example, the aperture disposed on the light source side of the objective lens is defined as the first surface, the radius of curvature of the i-th lens surface is ri, and the radius of curvature of the i-th surface and the (i + 1) -th surface is ri. It is represented by the refractive index ni at the wavelength of the luminous flux of the laser light source of the medium in between.

[0058]

[Table 3]

[0059]

[Table 4]

F = 3.17 mm NA0 = 0.63 At the light source wavelength λ = 680 nm of this embodiment,
The NA required for reading the first optical disk (for example, DVD), that is, NA1, is 0.60, and the NA required for reading of the second optical disk (for example, CD), that is, NA2, is 0.39 when the equalizer is not used together.

FIG. 7A is a diagram showing the spherical aberration when the substrate thickness t1 of the objective lens of this embodiment is 0.6 mm (corresponding to the substrate thickness of the first optical disk).

In FIG. 7 (a), in this objective lens, when the substrate thickness t1 = 0.6 mm, the spherical aberration is overcorrected near (1/2) NA2, that is, when the NA is 0.2. ), Near NA2, that is, when NA is 0.4
At a height of 0, the correction is complete. In the spherical aberration curve, the correction is insufficient (under) in the direction from (1/2) NA2 to the height of NA2. NA0 at this time
The best wavefront aberration in the range of (0.63) is about 0.02λ.
rms.

For this objective lens, the substrate thickness t1 =
FIG. 7B shows a light spot in a condensed state through a 0.6 mm transparent substrate, which is observed by setting an interference fringe to be substantially linear using an interferometer.

In the objective lens in which the spherical aberration is completely corrected, it is observed as parallel linear interference fringes. However, in the objective lens of this example, the spherical aberration is (1/1).
2) Overcorrection occurs near NA2, that is, when NA is at a height of 0.2, and is completely corrected near NA2, that is, when NA is at a height of 0.4, as shown in FIG. 7B. (1/2) A numerical aperture NA4 around NA2, that is, NA is larger than 0.2 and smaller than NA1 (or NA0).
(In this example, an interference fringe having a portion bent in a V shape near NA4 = NA2 = 0.39). That is, the objective lens of this example has the best wavefront aberration in which such interference fringes are observed.

Note that NA4 is expressed as (1/2) NA2 <NA4 <(1/2) (NA1 + NA
2) It is desirable that the following equation be satisfied (in the above formula, NA1 may be NA0 for practical purposes).

FIG. 8 shows that the objective lens has a substrate thickness t2 =
FIG. 9 is a diagram showing the relationship between NA, best wavefront aberration, and the amount of defocus at that time when the thickness is 1.2 mm (corresponding to the substrate thickness of the second optical disc).

In FIG. 8, (1/2) N of the objective lens
By correcting the luminous flux at the height of A2 more than the luminous flux at the height of NA2, the luminous flux at the height of NA2 becomes (1/2).
Since the light flux is lower than the light flux having the height of NA2, over-spherical aberration generated by the increase in the thickness of the substrate can be reduced. When NA = 0.41, the value is approximately 0.07λrms, which is within Marechal's limit. The best wavefront aberration at NA2 (NA = 0.39) is 0.1.
The objective lens can sufficiently read an optical disk of the CD system. Also, t1 = 0.6 mm
Reading of DVD type optical disk is also NA0 = 0.6
3, the best wavefront aberration is 0.02λrms, which is sufficiently small and can be performed well. In this example, the spherical aberration is reduced to t by the objective lens.
When the substrate thickness is 2 = 0.6 mm, (1/2) NA2
Is overcorrected than the luminous flux having the height of NA2, but this may be performed by, for example, a collimator lens. In short, the luminous flux emitted from the laser light source is t1 = 0.6 mm. When collected on the information recording surface of the optical disk via the substrate, the total (1/2)
It is sufficient that the light beam having the height of NA2 is overcorrected (over) than the light beam having the height of NA2.

According to this configuration, the loss due to the optical system is small, the emission efficiency can be increased, and the optical pickup device is suitable for recording on a writable optical disk.

(Embodiment 3) FIG. 9 is a diagram showing an optical pickup device according to Embodiment 3 of the present invention. FIG. 10 is a diagram of a mask having a ring-shaped light beam shielding portion.

FIG. 9 is a circuit diagram showing one of the second embodiment shown in FIG.
On the optical path between the 波長 wavelength plate 14 and the objective lens 6, FIG.
A mask having a ring-shaped light beam shielding portion as described above is provided, and by reading out the area of the light beam which is harmful when reading information from the second optical disk, the reading performance is further improved. .

In FIG. 9, the laser light source 11 (λ = 68
0 nm) from the polarization beam splitter 1
2. The light passes through the collimator lens 13 and the quarter-wave plate 14 to become a circularly polarized parallel light beam. This light beam passes through the ring-shaped mask 15, the light beam in the mask portion is cut, and the light beam is condensed on the information recording surface 8 via the substrate 7 of the optical disk by the objective lens 6. The light flux modulated and reflected by the information pits on the information recording surface 8 is again reflected by the objective lens 6, the ring-shaped mask 15, the ４ wavelength plate 14, and the collimator lens 13.
Is transmitted to the polarization beam splitter 12 and reflected there, and travels to the photodetector 19. Astigmatism is given by the cylindrical lens 10 arranged on the optical path to the photodetector 19, and the magnification is enlarged by the concave lens 16.
The configuration of the photodetector and the detection of the focus error signal, the track error signal, and the information signal are the same as in the second embodiment.

FIG. 11 shows the NA required for reading information from the second optical disc (for example, CD) when the light passes through the condensing optical system of this embodiment through a substrate having a substrate thickness of t2 = 1.2 mm.
FIG. 4 is a spherical aberration diagram including defocus at a position where the best wavefront aberration occurs in a range of 2.

In FIG. 11, the area from the axis to NA2 is a light beam effective for information reading, and the NA outside the area is NA2.
The region from 2 to NA0 is a light beam which does not contribute to reading and becomes a noise component. The portion of the light beam close to NA0 has an extremely large spherical aberration, so that it is in a defocused state on the information recording surface, and does not become a significant noise factor. The portion close to NA2 becomes flare light adjacent to a light beam effective for reading, and this light beam is modulated by information pits on the information recording surface. When the light beam enters the photodetector, it becomes a large noise, leading to jitter deterioration. For this reason, by providing a ring-shaped mask for blocking the light beam in the opening larger than the area of NA2 and smaller than NA1 (or NA0), it is possible to prevent the light beam which causes a noise increase from entering the photodetector. it can.

If the outer diameter of the mask portion is too large, the loss of light amount increases, and the performance of reading information from the first optical disk (eg, DVD) deteriorates. Therefore, it is preferable that the shielding of the light beam which is a noise component is the minimum necessary. Specifically, from the focal position where the best wavefront aberration is obtained in the range of NA2,
It cuts the light flux that focuses one to two times behind the depth of focus. The depth of focus is given by λ / (2 × NA ² ),
It is approximately 2.2 μm when λ = 680 nm and NA = 0.39, which corresponds to a light beam with NA = 0.42 in the present focusing optical system. When NA = 0.47, the distance is about 4.7 μm behind, which is twice the depth of focus. Therefore, it is good to set NA = 0.39 inside the light beam shielding ring and NA = 0.42 to 0.47 outside.

This mask is not necessarily shielded by absorbing a light beam, but may be based on the effects of reflection, scattering, refraction, diffraction, etc., as long as the light beam returning to the photodetector can be cut. Further, this mask may be integrated with other optical elements such as a collimator lens, an objective lens, and a beam splitter, instead of as an independent component.

In particular, it is preferable that the shielding portion in the light beam incident on the information recording surface does not shift even if the objective lens shifts due to tracking, if it is provided integrally with the incident side optical surface or the emission side optical surface of the objective lens.

This mask may be reflected at the information recording surface from the laser light source via the objective lens, and may be located anywhere on the optical path toward the photodetector. In particular, it is preferable that the light beam from the laser light source be guided to the information recording surface more effectively when it is arranged in the optical path from the beam splitter to the photodetector.

In the above example, the mask has a ring shape. However, among the ring-shaped light beam shielding portions shown in FIG. 10, the cylindrical lens of the photodetector shown in FIG. 6 is used. Leaving portions corresponding to the regions of the light receiving sections A and C (or B and D) at the diagonal positions in the same direction as the generatrix,
Other portions may be formed as a mask having a light beam shielding portion for transmitting light. By doing so, it is possible to reduce the light amount loss at the time of reading and writing of the first optical disk, and to reduce the light flux that is incident on the photodetector at the time of reading the second optical disk and causes an increase in noise.

(Embodiment 4) FIGS. 12A and 12B are diagrams showing the element configuration of an eight-segment photodetector. FIG. 12A is a diagram showing the element configuration, and FIG. 12B is a diagram showing the element thickness of the transparent substrate. FIG. 3C is a diagram showing a light-collecting state of a light beam from a 6-mm first optical disk (for example, a DVD); FIG.

In FIG. 5 of the second embodiment, instead of the four-segment photodetector, an eight-segment photodetector as shown in FIG. 12A is used, and the element for detecting the information signal is switched according to the type of the optical disk. Thereby, the reproduction performance can be further improved.

FIG. 12B shows that the thickness of the transparent substrate t = 0.
This shows a state in which a light beam from the 6 mm first optical disk is converged on the eight-segment photodetector.

The dividing line S has a direction substantially coincident 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.

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 + D2) or (A2 + B2 + C2 + D2) only in the outer peripheral portion.
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.

FIG. 12C shows that the thickness t = 1.
This represents a state where a light beam from the 2 mm second optical disk is converged on the eight-segment photodetector.

The light has a high light intensity at the center, and the outside becomes a flared light condensate. The light is mainly received at the center (A
1 + B1 + C1 + D1) to detect an information signal. This light receiving range is desirably within the light beam of NA2.

The focus error signal is obtained by (A1 + A2 + C1 + C2)-(B1 + B2 + D1 + D) by the astigmatism method.
2) or (A1 + C1)-(B1 + D1) The track error signal is obtained by the push-pull method (A1 + A
2 + B1 + B2)-(C1 + C2 + D1 + D2) or (A1 + B1)-(C1 + D1).

By dividing the photodetector in the area for detecting the information signal as described above, it is possible to detect a signal in an area free from flare light due to spherical aberration generated by a substrate such as a CD having t = 1.2 mm. The reproduction performance is improved. or,
By providing a ring-shaped light-shielding portion of NA2 or more and NA1 (or NA0) or less, desirably 1.2NA2 or less in the optical path, it is possible to further reduce the jitter by cutting off the light flux that becomes a noise component.

[0089]

According to the present invention, it is possible to read a CD-type optical disc having a significantly different substrate thickness and information recording density by a compact DVD pickup optical pickup device having a simple structure. An optical pickup device, an objective lens of the optical pickup, and an optical disk device which have good emission efficiency and can perform writing with a lower laser power by a recording method have been provided.

[Brief description of the drawings]

FIG. 1 is a diagram of an optical pickup device conventionally considered.

FIG. 2 is a diagram illustrating a relationship between substrate thickness and best wavefront aberration.

FIG. 3 is a diagram illustrating an optical pickup device according to a first embodiment;

FIG. 4 is a diagram illustrating a relationship between NA, best wavefront aberration, and optimum defocus when a substrate of t = 1.2 mm according to the first embodiment;

FIG. 5 is a diagram illustrating an optical pickup device according to a second embodiment;

FIG. 6 is a diagram illustrating an element configuration of a photodetector according to a second embodiment.

FIG. 7 is a diagram showing a spherical aberration of the objective lens according to the second embodiment and an interference fringe of a light spot.

FIG. 8 shows that the objective lens according to the second embodiment has t2 = 1.2 m.
FIG. 9 is a diagram illustrating a relationship between NA, best wavefront aberration, and optimum defocus for an m substrate.

FIG. 9 is a diagram illustrating an optical pickup device according to a third embodiment;

FIG. 10 is a diagram of a mask having a ring-shaped light beam shielding portion according to a third embodiment.

FIG. 11 is a diagram illustrating spherical aberration of an objective lens of an optical pickup according to a third embodiment;

FIG. 12 is a diagram illustrating an element configuration of an eight-segment photodetector according to a fourth embodiment.

[Explanation of symbols]

 Reference Signs List 1,11 Laser light source 2 Hologram beam splitter 3,13 Collimator lens 5,51 Aperture 6,61 Objective lens 7 Substrate 8 Information recording surface 9,19 Photodetector 10 Cylindrical lens 12 Polarizing beam splitter 14 Quarter wave plate 15 Ring Mask 16 concave lens

Claims (14)

[Claims] 1. A light beam emitted from a laser light source is condensed as a light spot on an information recording surface by a condensing optical system via a transparent substrate of an optical information recording medium, and reflected light from the information recording surface is converted to light. In an optical pickup device for receiving information from a detector and reproducing information, a condensing optical system for obtaining, at a wavelength λ, a light spot capable of reading information from a first optical information recording medium having a thickness t1 of a transparent substrate and an information recording density i1. Required numerical aperture on the optical information recording medium side
1. The necessary numerical aperture on the optical information recording medium side of the optical information recording medium side of the condensing optical system for obtaining a light spot at a wavelength λ from which information on the second optical information recording medium can be read with a thickness t2 of the transparent substrate and an information recording density i2.
When the numerical aperture NA0 of the condensing optical system on the optical information recording medium side is N,
A1 or more, the best wavefront aberration of the light spot when passing through the transparent substrate of thickness t1 is 0.05λrms or less, and the best wavefront aberration of the light spot when passing through the transparent substrate of thickness t2 is NA2. The optical pickup device is set to 0.07 λrms or less within the range. However, t1
<T2, i1> i2, NA1> NA2, λ is the wavelength of the laser light source. 2. A light beam emitted from a laser light source is condensed as a light spot on an information recording surface via a transparent substrate of an optical information recording medium by a condensing optical system, and reflected light from the information recording surface is converted to light. In an optical pickup device for receiving information from a detector and reproducing information, a condensing optical system for obtaining, at a wavelength λ, a light spot capable of reading information from a first optical information recording medium having a thickness t1 of a transparent substrate and an information recording density i1. Required numerical aperture on the optical information recording medium side
1. The necessary numerical aperture on the optical information recording medium side of the optical information recording medium side of the condensing optical system for obtaining a light spot at a wavelength λ from which information on the second optical information recording medium can be read with a thickness t2 of the transparent substrate and an information recording density i2.
When the numerical aperture NA0 of the condensing optical system on the optical information recording medium side is N,
A1 or more, the best wavefront aberration of the light spot when passing through the transparent substrate having the thickness t1 is 0.05λrms or less, and in the optical path from the laser light source to the light detector via the condensing optical system, An optical pickup device provided with a ring-shaped light beam shielding portion that is larger than NA2 and smaller than NA1. Where t1 <t2, i1> i2, NA
1> NA2, λ is the wavelength of the laser light source. 3. A light beam emitted from a laser light source is condensed as a light spot on an information recording surface via a transparent substrate of an optical information recording medium by a condensing optical system, and reflected light from the information recording surface is converted to light. In an optical pickup device for receiving information from a detector and reproducing information, a condensing optical system for obtaining, at a wavelength λ, a light spot capable of reading information from a first optical information recording medium having a thickness t1 of a transparent substrate and an information recording density i1. Required numerical aperture on the optical information recording medium side
1. The necessary numerical aperture on the optical information recording medium side of the optical information recording medium side of the condensing optical system for obtaining a light spot at a wavelength λ from which information on the second optical information recording medium can be read with a thickness t2 of the transparent substrate and an information recording density i2.
When the numerical aperture NA0 of the condensing optical system on the optical information recording medium side is N,
A1 or more, the best wavefront aberration of the light spot when passing through the transparent substrate having the thickness t1 is 0.05λrms or less, the photodetector is divided into a plurality of regions, and the first and second optical information An optical pickup device wherein an area for reproducing an information signal is made different from that of a recording medium. Where t1 <t2, i1> i2, NA1> NA2, and λ are the wavelengths of the laser light source. 4. The optical pickup device according to claim 3, wherein an area of the photodetector for reproducing the information signal of the second optical information recording medium is an area corresponding to the range of NA2. 5. An optical path which is larger than NA2 on the optical path from the laser light source to the photodetector via the focusing optical system.
5. The optical pickup device according to claim 3, wherein a ring-shaped light shielding portion smaller than 1 is provided. 6. The spherical aberration of the converging optical system when passing through a transparent substrate having a thickness t1 is (1/1/2)
2) The optical pickup device according to any one of claims 1 to 5, wherein the luminous flux of NA2 is overcorrected. However, (1/2) NA2 is 1 / NA2
2 shall be represented. 7. The thickness t1 of the transparent substrate is 0.6 mm, the numerical aperture NA0 is λ (μm) /1.14 (μm) or more, the thickness t2 of the transparent substrate is 1.2 mm, and the numerical aperture NA2 is λ.
(Μm) /1.75 (μm) or λ (μm) / 2.
The optical pickup device according to any one of claims 1 to 6, wherein the diameter of the optical pickup device is 46 (μm). 8. An optical pickup for converging a light beam from a laser light source as a light spot on an information recording surface of an optical information recording medium via a transparent substrate and reading out information recorded on the information recording surface. In the objective lens, the required numerical aperture on the optical information recording medium side of the objective lens for obtaining a light spot at a wavelength λ from which information of the first optical information recording medium having a thickness t1 of the transparent substrate and an information recording density i1 can be read. NA
1. The required numerical aperture of the objective lens on the optical information recording medium side for obtaining a light spot at a wavelength λ from which information of the second optical information recording medium can be read with a thickness t2 of a transparent substrate and an information recording density i2 is NA.
When the objective lens of the optical pickup is 2, the best wavefront aberration when passing through the transparent substrate having the thickness t1 is 0.05 λrms or less, and the luminous flux of (１ ／) NA2 is corrected more than the luminous flux of NA2. An objective lens for an optical pickup, characterized in that a ring-shaped light shielding portion is provided on an entrance surface or an exit surface of an area having an excessive (over) spherical aberration and larger than NA2 and smaller than NA1. Where t1 <t2, i1> i2,
NA1> NA2, λ is the wavelength of the laser light source, and (1/1)
2) NA2 represents 1/2 of NA2. 9. A light beam emitted from a laser light source is condensed as a light spot on an information recording surface via a transparent substrate of an optical information recording medium by a condensing optical system, and reflected light from the information recording surface is detected. In the optical pickup device for receiving and reading information from the optical information recording medium, the light-collecting optical system is required to reproduce the information of the optical information recording medium having the transparent substrate having a thickness of t1 with light having a wavelength of λ. Of the optical information recording medium of the condensing optical system necessary for reproducing the information of the optical information recording medium at t2 in which the thickness of the transparent substrate is greater than t1 with light of the wavelength λ. NA2
(<NA1), When the numerical aperture on the optical information recording medium side of the condensing optical system that is larger than NA2 and smaller than NA1 is NA3, the numerical aperture NA0 on the optical information recording medium side of the condensing optical system is:
The best wavefront aberration of a light spot when passing through a transparent substrate having a thickness of t1 at NA1 or more is 0.07λr.
ms or less, of the reflected light reaching the photodetector after being reflected by the information recording surface of the optical information recording medium, the NA3 to NA2 of the lens surface of the light-collecting optical system closest to the optical information recording medium A light beam shielding unit that shields at least a part of a ring-shaped light beam that passes through a range and reaches the photodetector is provided in an optical path between an optical information recording medium and the photodetector. Optical pickup device. 10. The optical pickup device according to claim 9, wherein the light-shielding portion is formed on a surface of the objective lens of the focusing optical system on the side of the laser light source. 11. The NA2 is λ (μm) /1.75.
The optical pickup device according to claim 9, wherein the optical pickup device is (μm). 12. The NA2 is λ (μm) /2.46.
The optical pickup device according to claim 9, wherein the optical pickup device is (μm). 13. The NA3 is 1.1NA2 to 1.2N.
A2 according to any one of claims 9 to 12,
An optical pickup device according to the item. 14. The optical information recording medium according to claim 1, wherein the thickness of the transparent substrate is t2 and the objective lens of the optical pickup device or the focusing optical system of the optical pickup. An optical disk device, comprising: focusing control means for performing focusing control so that the objective lens of the condensing optical system is focused farther than the paraxial focus when reproducing the information of (1) with light of wavelength λ.