JPH0927138A - Optical reproducing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize the reproducing of optical disks whose thicknesses are different with a device whose structure is simple and which is of inexpensive. SOLUTION: In this device, an objective lens 2 in which the thickness of a disk is designed by a disk thickness of 0.8mm between disk thicknesses of the thickness of 0.6mm and the thickness of 1.2mm is used. Then, information written on recording surfaces are read out by focusing the diameter of a convergent spot on recording surfaces of disk thickness of the thickness of 0.6mm and the thickness of 1.2mm while changing the numerical aperture of the objective lens 2 by thicknesses of the disks.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical reproducing apparatus suitable for reproducing a plurality of types of optical recording media having different disk substrate thicknesses.

[0002]

2. Description of the Related Art As a conventional technique of this kind, JP-A-6-25
The technology of the recording / reproducing apparatus for an optical recording medium disclosed in Japanese Patent Publication No. 9804 can be mentioned.

In this technique, first and second light sources, a laser beam synthesizing means for synthesizing laser beams from the respective light sources into substantially the same optical path, and a laser beam from the first light source for the first optical disk are used. From the first and second optical discs, a converging light source system for converging light and converging laser light from the second light source for the second optical disc having a disc substrate thickness different from that of the first optical disc It is composed of a photodetector that receives the reflected light of the.

As a result, two disc substrates having different thicknesses are formed.
A thin optical disc that can support various types of optical discs and has a higher density by increasing the numerical aperture of the objective lens.
Recording / reproduction can be performed on a conventional 1.2 mm optical disc, and a single optical head can achieve high density without sacrificing compatibility, which enables downsizing and cost reduction.

[0005]

A conventional recording / reproducing apparatus for an optical recording medium of this type is, specifically, an independent optical system of two systems having an objective lens and a quarter wavelength plate in common. It has two types of optical discs with different disc substrate thicknesses. At this time, the disc substrate thicknesses of the two different types of optical discs are determined, and which of the two optical systems is to be selected is determined. There is a need to. An apparatus for discriminating the disc substrate thicknesses of two different types of optical discs is indispensable.

Therefore, in the technique disclosed in Japanese Unexamined Patent Publication No. 6-215406, the light source and the reflected light from the optical disk and the objective lens that converges the light emitted from the light source to two image forming points having different focal lengths are detected. And a signal detecting means for controlling one of the two image forming points are formed on the optical disk.

With this configuration, two image forming points formed by the objective lens are provided, and it is possible to deal with two types of optical disks having different thicknesses. Therefore, recording and playback can be performed on both thin optical discs and conventional optical discs whose objective lens has a higher numerical aperture for higher density.
Higher density can be achieved without sacrificing compatibility.

However, although the technique disclosed in this publication has a simple structure, the provision of two imaging points formed by the objective lens complicates the configuration of the objective lens,
There is a problem that the objective lens becomes expensive.

Therefore, an object of the present invention is to provide a compatible pickup device for an optical recording medium, which makes it possible to reproduce optical discs having different thicknesses with a simple structure and at a low cost.

[0010]

In order to reproduce an optical recording medium having different disk substrate thicknesses, an optical reproducing apparatus according to a first aspect of the invention forms a reproduction beam at a position shallower than a thick disk substrate and deeper than a thin disk substrate. It is equipped with an objective lens designed to collect light.

An optical reproducing apparatus according to a second aspect of the invention further changes the numerical aperture of the objective lens according to the thickness of the disk substrate of the optical recording medium to be reproduced.

According to a third aspect of the present invention, the reproducing apparatus further sets the numerical aperture of the numerical aperture changing means so that the focused spot on the recording surface of the optical recording medium to be reproduced becomes small.

An optical reproducing apparatus according to a fourth aspect of the present invention includes an annular liquid crystal shutter that selectively shields the light incident on the objective lens from the outer side.

An optical reproducing apparatus according to a fifth aspect is a liquid crystal shutter made of an annular guest-host type liquid crystal that selectively shields the light incident on the objective lens from the outside.

An optical reproducing apparatus according to a sixth aspect of the present invention is an annular polarization filter that selectively shields the light incident on the objective lens from the outer side.

An optical reproducing apparatus according to a seventh aspect is an annular polarization-selective hologram that selectively shields the outer side of the light incident on the objective lens.

An optical reproducing apparatus according to an eighth aspect is an annular polarizing glass which selectively shields the outer side of the light incident on the objective lens.

According to a ninth aspect of the present invention, there is provided an optical reproducing apparatus in which the disc substrate thicknesses of a plurality of types of optical recording media are 1.1 to 1.3.
mm and 0.55 to 0.65 mm, the objective lens is focused to a depth of 0.7 to 0.9 mm.

An optical reproducing apparatus according to a tenth aspect of the present invention condenses the objective lens at a depth of 0.8 mm.

In the optical reproducing apparatus according to the eleventh aspect, when reproducing an optical recording medium having a disk substrate thickness of 1.1 to 1.3 mm, the numerical aperture of the objective lens is set to 0.43 to 0.47, When reproducing an optical recording medium having a disc substrate thickness of 0.55 to 0.6 mm, the numerical aperture of the objective lens is set to 0.50 to 0.50.
It is set to 0.55.

An optical reproducing apparatus according to a twelfth aspect inputs to a correction circuit for changing the reproduction output characteristic according to the recording medium to be reproduced.

The correction circuit of the optical reproducing apparatus according to the thirteenth aspect further enhances the high frequency characteristic and increases the crosstalk correction amount.

An optical reproducing apparatus according to a fourteenth aspect is provided with a filter for shielding the central portion of the light incident on the objective lens.

An optical reproducing apparatus according to a fifteenth aspect has an intersymbol interference canceling circuit for switching a circuit constant depending on the type of recording medium.

[0025]

According to the first aspect of the present invention, a focused spot that is slightly larger than the focused position is formed off the focused position.

In the second aspect, the focused spot size is changed by changing the numerical aperture of the objective lens.

In the third aspect, the focused spot size is reduced by changing the numerical aperture.

In the fourth aspect, the condensed spot size is changed by the liquid crystal shutter.

In the present invention, the condensed spot size is changed by the liquid crystal shutter made of guest-host type liquid crystal.

In the sixth aspect, the condensing spot size is changed by the annular polarization filter.

According to the seventh aspect of the present invention, the condensed spot size is changed by the polarization selective hologram.

According to the eighth aspect, the condensed light spot size is changed by the polarizing glass.

In the ninth aspect, the disk substrate 1.1
0.7 between 0.3 mm and 0.55 to 0.65 mm
Light is focused to ~ 0.9 mm.

In the tenth aspect, the disk substrate 1.
0.1 between 1.3 mm and 0.55 to 0.65 mm.
Light is focused on 8 mm.

In the eleventh aspect, the focused spot size is about 1.0 μm on the disk substrate of 0.6 mm,
With a 1.2 mm disk substrate, the focused spot size is about 1.2 μm.

In the twelfth aspect, the reproduction characteristic is optimally corrected according to the type of the recording medium to be reproduced.

In the thirteenth aspect, when reproducing the optical recording medium, the high frequency band is emphasized and the crosstalk correction amount is increased.

In the fourteenth aspect, the focused spot size becomes small due to the super-resolution phenomenon.

In the fifteenth aspect, intersymbol interference caused by super-resolution is eliminated.

[0040]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below.

Note that, in the drawings, the same reference numerals and symbols indicate the same or corresponding components, and therefore, duplicated description will be omitted.

FIG. 1 is an overall configuration diagram of an optical reproducing apparatus according to the first embodiment of the present invention. FIG. 2 is a plan view of an annular light shielding filter used in the optical reproducing device of the first embodiment of the present invention. Further, FIG. 10 is an explanatory diagram showing an operation principle for explaining a guest-host type liquid crystal forming an annular light shielding filter used in the optical reproducing apparatus of the first embodiment of the present invention, and FIG. 11 is the first embodiment of the present invention. FIG. 3 is a schematic diagram illustrating a polarizing glass forming an annular light shielding filter used in the optical reproducing apparatus of FIG.

As shown in FIG. 1, the semiconductor laser 8 has 63
It is a red semiconductor laser of 5 (tolerance ± 15) nm,
Outputs laser light. The diffraction grating plate 7 splits the light into three beams of 0th order light and ± 1st order light. The collimator lens 6 collimates the laser light emitted from the semiconductor laser 8 and split into three beams of 0th order light and ± 1st order light by the diffraction grating plate 7 into parallel light. The polarization beam splitter 5 allows the laser light from the semiconductor laser 8 to pass therethrough and totally reflects the reflected light from the disk 1. λ
The / 4 plate 4 converts linearly polarized light into circularly polarized light or converts circularly polarized light into linearly polarized light, and collects it with a condensing lens group 9 including a spherical lens, and the objective lens 2 has a laser beam that has passed through a polarization beam splitter 5. Focus the light.

The annular light-shielding filter 3 as the numerical aperture changing means for changing the numerical aperture according to the disc substrate thickness of the optical recording medium to be reproduced in this embodiment has a numerical aperture (hereinafter simply referred to as "NA") depending on the thickness of the disc 1. 2), specifically, as shown in FIG. 2, it is composed of a liquid crystal shutter having an annular pattern, and shields the outer peripheral portion of the beam incident on the objective lens 2. Here, the guest-host type liquid crystal 300 is preferable as the liquid crystal shutter.

Besides the liquid crystal, a polarizing filter, a polarization selective hologram, or a polarizing glass 310 may be used.
However, the configuration of the optical system at this time is the configuration of FIG. 12 described later.

As shown in FIG. 10, the guest-host type liquid crystal 300 described above is provided with the guest-host type liquid crystal 300 outside the through hole, and only when no voltage is applied, that is, in the OFF state (a), the entire surface is formed. This is an element that exhibits polarization selection characteristics only when transmission and voltage are applied, that is, in the ON state (b). In addition, the polarizing glass 31 described above
As shown in FIG. 11, 0 is a state in which the silver compound is oriented in a certain direction in the glass, and when no voltage is applied,
1 (a) is transparent, and the outer periphery of the surface is reduced to deposit silver, and the reduced silver film is shown in FIG.
As shown in (b), it exhibits a polarization characteristic when a voltage is applied. The material silver may be another metal material as long as it has polarization selectivity.
Also, the NA can be changed by physically shielding the outer peripheral portion of the beam, such as by mechanically inserting a diaphragm.

The photodetector 10 is composed of a first light receiving element for receiving the 0th order light by dividing it into four, a second light receiving element for receiving the ± 1st order light, and a third light receiving element.

The entire optical reproducing apparatus of this embodiment having the above structure operates as follows.

The laser beam emitted from the semiconductor laser 8 having a wavelength of 635 (tolerance ± 15) is 0 at the diffraction grating plate 7.
The light is split into three beams of secondary light and ± first-order light, and a thickness of 0.6 (permissible error ± 0.05) mm is passed through the collimator lens 6, the polarization beam splitter 5, the λ / 4 plate 4, and the objective lens 2. The light is incident on the disk 1 and focused on the recording surface.
On this recording surface, the condensed 0th-order light is irradiated to the center of the recording track, and the condensed ± 1st-order light is irradiated to positions slightly deviated on both sides of the recording track.

The laser beam reflected from the recording surface is separated by the polarization beam splitter 5 via the objective lens 2 and the λ / 4 plate 4, and the photodetector 10 via the condenser lens group 9.
Is collected.

Further, the optical reproducing apparatus of this embodiment will be described in detail.

The objective lens 2 of this embodiment is the disc 1
Is a lens designed with a substrate thickness of 0.8 mm,
The objective lens 2 is designed to have a numerical aperture (hereinafter, simply referred to as “NA”) of 0.52 to 0.6.

Using the objective lens 2 designed to have a thickness of 0.8 mm and laser light having a wavelength of 635 nm, a thickness of 0.6 is obtained.
When focusing on a disc 1 of mm, N of the objective lens 2
The relationship between A and the focused spot diameter is as shown in FIG.

That is, the minimum value is obtained in the vicinity of NA = 0.52. The spot diameter at this time is about 1 μm.

FIG. 3 shows the relationship between the NA and the focused spot diameter when the 0.8 mm objective lens used in the optical reproducing apparatus of the first embodiment of the present invention is focused on a 0.6 mm thick disk substrate. FIG. Further, FIG. 4 shows the case where the 0.8 mm objective lens used in the optical reproducing apparatus of the first embodiment of the present invention is used for focusing on a disk substrate having a thickness of 1.2 (tolerance ± 0.1) mm. It is a characteristic view which shows the relationship between NA and a condensing spot diameter.

Here, when the objective lens 2 designed to have a thickness of 0.8 mm and a laser beam having a wavelength of 635 nm are used to focus light on the disk 1 having a thickness of 0.6 mm, the NA of the objective lens 2 and the focused spot diameter. The relationship has a minimum value in the vicinity of NA = 0.52. The spot diameter at this time is about 1 μm
Becomes

On the other hand, in a high density digital video disc (DVD) using a disc having a disc substrate thickness of 0.6 mm, laser light having a wavelength of 650 nm or 635 nm and an objective lens having NA = 0.6 are used. Approximately 0.95 for a pickup that uses a combination of laser light of this wavelength and NA.
It is a focused spot diameter of μm.

Therefore, in the pickup using the laser beam having the wavelength of 635 nm and the objective lens 2 having NA = 0.52, the spot diameter when focused on a 0.6 mm disk is about 1 μm, and therefore, the value of 0. This is not a big difference as compared with the spot diameter of 0.95 μm, which is the focused spot diameter of the pickup for a high-density optical disc represented by a 6 mm DVD.

That is, the NA when the 0.8 mm objective lens 2 is used and the light is focused on the disk 1 having a thickness of 0.6 mm.
It is possible to reproduce a high-density optical disk represented by a DVD having a thickness of 0.6 mm with a laser beam having a wavelength of = 0.52 and a wavelength of 635 mm. However, since the difference in spot diameter appears as the difference in frequency characteristic during reproduction, 635 nm, NA = 0.
When the 0.6 mm disc is reproduced by the pickup 52, it is necessary to raise the high frequency level of the reproduced signal by using the waveform equivalent circuit by the waveform equivalent circuit switching unit 25 or the like. Further, by changing the characteristic of the waveform equivalent circuit, it becomes possible to use the NA in the range of 0.50 to 0.55.

Further, 0.8 designed to have a thickness of 0.8 mm
When an objective lens 2 for mm and a laser beam having a wavelength of 635 nm are used to focus on a disc 1 having a thickness of 1.2 mm,
The relationship between the NA of the objective lens 2 and the focused spot diameter is as shown in FIG. 4, and has a minimum value near NA = 0.45. The spot diameter at this time is about 1.2 μm.

On the other hand, a DVD having a disk substrate thickness of 1.2 mm
In the high-density optical disk represented by, the laser light having a wavelength of 635 nm and the objective lens 2 having NA = 0.52 are used. A pickup combining a laser beam of this wavelength and NA has a focused spot of about 1.1 μm.

Therefore, in the pickup using the laser light having the wavelength of 635 nm and the objective lens 2 having NA = 0.45, the spot diameter when condensed on the 1.2 mm disk is about 1.2 μm, 1.2mm DVD
This is not a big difference as compared with 1.1 μm, which is the focused spot diameter of the high-density optical disc pickup typified by 1.
Therefore, it is possible to reproduce a high-density optical disc represented by a 1.2 mm thick DVD with a 0.8 mm objective lens 2 designed for 0.8 mm, a 635 nm laser beam, and a NA = 0.45 pickup. Is. However, since the difference in spot diameter appears as the difference in frequency characteristics during reproduction, 6
1.2 with 35nm, NA = 0.45 pickup
Similarly, when reproducing a mm disc, it is necessary to raise the high frequency level of the reproduced signal by the waveform equivalent circuit. Further, by changing the characteristics of this waveform equivalent circuit, the above N
It becomes possible to use A in the range of 0.43 to 0.47.

Thus, in this embodiment, 0.8 mm
Since the objective lens 2 designed for thickness is used for discs 1 having two thicknesses of 0.6 mm and 1.2 mm, the NA of the objective lens 2 corresponding to the thickness of each disc 1 Since the amount of lifting in the high frequency band is different from that in switching, it is also necessary to switch the waveform equivalent circuit.

When reproducing a disc having any one of the two types of discs 1 having thicknesses of 0.6 mm and 1.2 mm, the spot diameter is slightly larger than that of the regular disc. (Direction) resolution is also slightly reduced, and crosstalk from adjacent tracks may increase. Therefore, it is preferable to provide a crosstalk removing circuit for each disk and switch them.

Further, since the disc of the disc 1 having two kinds of thicknesses of 0.6 mm and 1.2 mm has different track pitches, the level of the obtained tracking signal also differs.
Therefore, it is desirable to provide a tracking servo circuit or constant having a gain corresponding to the disc and switch this.

In addition, since the two types of discs having different thicknesses described above have different modulation systems for the signals to be recorded, a demodulation circuit corresponding to each is required, and it is necessary to switch these.

Therefore, the reproduction control circuit shown in FIG. 5 is usually used in the optical reproduction apparatus of this embodiment.

FIG. 5 is a block diagram of a reproduction control circuit used in the optical reproducing apparatus of this embodiment.

The disc thickness discriminating section 21 discriminates the thickness of the disc 1 automatically or manually. The control unit 22
A selection signal is output to the NA switching unit 23, the servo circuit switching unit 24, the waveform equivalent circuit switching unit 25, the crosstalk removal circuit switching unit 26, and the demodulation circuit switching unit 27 based on the information of the disk thickness determination unit 21.

First, the NA switching section 23 sets the annular light-shielding filter 3 to have NA = 0.52 and a thickness of 1.2 when reproducing a high-density optical disk represented by a DVD having a thickness of 0.6 mm.
When reproducing a high-density optical disc represented by a mm DVD, the annular light-shielding filter 3 is switched to NA = 0.45. That is, from the NA = 0.52 when reproducing a high-density optical disc typified by a 0.6 mm thick DVD,
When reproducing a high density optical disc represented by a DVD having a thickness of 1.2 mm, the NA is switched to NA = 0.45 to lower the NA. As a specific example of this, as shown in FIG. 1, a liquid crystal shutter or the like having an annular pattern below the objective lens 2 is used to block the outer peripheral portion of the beam incident on the objective lens 2. The servo circuit switching section 24 receives the signal from the control section 22 and receives the photodetector 1
The reflected light of the ± first order beams from 0 is transmitted to the second light receiving element and the third light receiving element.
The light receiving element receives the light and receives a tracking signal, which is switched according to the thickness of the disk 1 and its recording density. Further, the waveform equivalent circuit switching unit 25 inputs the reproduction signal in which the reflected light of the 0th order beam from the photodetector 10 is received by the first light receiving element, and the focused spot diameter of the pickup is larger than that of the normal one. This is to compensate for the deterioration of the frequency characteristic caused by the slightly large value. That is, if the focused spot diameter is slightly larger than the regular one, the resolution will be slightly reduced in the single radial direction (tracking direction), so the high-frequency component is lifted and the high-frequency signal level is increased. Secure. When the focused spot diameter is slightly larger than that of the normal one, the crosstalk removing circuit switching unit 26 receives read signals from adjacent tracks only from a single radial direction. Therefore, crosstalk removal is provided corresponding to each disk according to the focused spot diameter and the recording density, and it is switched. The demodulation circuit switching unit 27 switches the decoding process according to the recording density.

Therefore, when the disc thickness determination unit 21 outputs the disc thickness automatically or manually, the control unit 22 determines the NA switching unit 23, the servo circuit switching unit 24, the waveform based on the information of the disc thickness determination unit 21. Equivalent circuit switching unit 2
5. The crosstalk removing circuit switching unit 26 and the demodulation circuit switching unit 27 are selectively switched. In the NA switching unit 23, 0.6
When reproducing a high-density optical disc represented by a mm-thick DVD, the annular light-shielding filter 3 is NA = 0.52, and when reproducing a high-density optical disc represented by a 1.2-mm thick DVD, an annular light-shielding filter is used. Switch 3 to NA = 0.45. In the servo circuit switching unit 24, a tracking signal in which the reflected light of the ± first-order beams from the photodetector 10 is received by the second light receiving element and the third light receiving element is input, and the tracking signal is set to the thickness of the disk 1 and its recording density. Switch accordingly.

Further, the waveform equivalent circuit switching section 25 for inputting the reproduction signal in which the reflected light of the 0th order beam from the photodetector 10 is received by the first light receiving element is compared with that of a pickup having a regular focused spot diameter. Therefore, the crosstalk removal circuit switching unit 26 removes the crosstalk according to the focused spot diameter and the recording density, and the demodulation circuit switching unit 27 performs the recording density according to the recording density. Then, the decryption processing is performed and reproduced output is performed.

The waveform equivalent circuit switching unit 25 can also be implemented as shown in FIG.

FIG. 6 is an overall configuration diagram of the optical reproducing apparatus of the second embodiment of the present invention, and FIG. 7 is a band-shaped filter (a) of a super-resolution filter used in the optical reproducing apparatus of the second embodiment of the present invention.
8 is a functional diagram of the band-shaped filter (a) and the circular filter (b) of the super-resolution filter of FIG. 7. FIG. 9 is a block diagram of a reproduction control circuit used in the optical reproducing device of the second embodiment of the present invention. In the drawings, the same reference numerals and symbols as those of the previous embodiment indicate the same or corresponding components as those of the previous embodiment, and therefore only the differences will be described here.

The difference between this embodiment and the first embodiment is that
Optical system polarization beam splitter 5 and collimator lens 6
The super-resolution filter 240 is placed in the optical path between and.

The super-resolution filter 240 is a filter that shields light or changes the phase in a band shape or a circle shape. That is, as shown in FIG. 7, the band-shaped filter (a) of the super-resolution filter 240 is inserted in the direction in which the side lobes and the main lobes are aligned on the track on the disc 1. Further, in the case of the circular filter (b) of the super-resolution filter 240, side lobes occur in a ring shape.

A band-shaped filter (a) as a super-resolution filter
When using, the focused beam profile is shown in Fig. 8 (a).
become that way. The plane of the focused beam on the recording surface is shown in FIG.
(B). In this optical system, the side lobes in the pit direction (track direction) cause intersymbol interference, so that the intersymbol interference elimination circuit switching unit 30 is required during reproduction as shown in FIG.

By the way, in the above embodiment, 0.6 mm
And the case of using the objective lens 2 designed with the disk substrate thickness of 0.8 mm for the disk thickness of 1.2 mm and 1.2 mm, the case where the present invention is carried out has different disk thicknesses. On the other hand, it is sufficient to use the objective lens 2 designed with a disc thickness between them.

As described above, in the optical reproducing apparatus of the above embodiment, for the disc thicknesses of 0.6 mm and 1.2 mm which are different from each other, the objective lens 2 designed with the disc thickness between the respective thicknesses is used. And by changing the NA of the objective lens 2 according to the disc thickness,
Information recorded on the recording surface is read by narrowing the focused spot diameter on the recording surfaces having different disk thicknesses, which can be an embodiment corresponding to the claims. Therefore, it is possible to reproduce the discs 1 having different thicknesses with a simple structure and at a low cost.

In the optical reproducing apparatus of the above embodiment, the disc thicknesses of 0.6 mm and 1.2 mm are:
Having an objective lens 2 designed with 0.8 mm in between,
Then, the N of the objective lens 2 is changed according to the disc thickness.
By changing A, a thickness of 0.6 mm and a thickness of 1.
Focus the focused spot diameter on the recording surface with a disc thickness of 2 mm,
The information written on the recording surface is read, and this can be an embodiment corresponding to the claims. Therefore, it is possible to reproduce the discs 1 having different thicknesses with a simple structure and at a low cost. Two types of D of 0.6mm and 1.2mm can be obtained with one pickup, especially by simple electrical or optical correction of the focused spot diameter.
It is possible to reproduce a high density optical disc represented by VD. It should be noted that the designed value of the objective lens 2 of 0.8 mm enables a tentative reproduction even if the allowable range is set to 0.7 to 0.9.

The optical reproducing apparatus of the above embodiment is
N of the objective lens 2 changed according to the disc thickness
In A, the NA of the objective lens 2 is selected so that the diameter of the condensed spot condensed on the recording surface of the disk is minimized, and this can be an embodiment corresponding to the claims. Therefore, it is possible to minimize the reading of signals other than desired information due to the large focused spot diameter.

FIG. 12 is an overall configuration diagram of the optical reproducing apparatus of the third embodiment of the present invention. In the drawings, the same reference numerals and symbols as those of the previous embodiment indicate the same or corresponding components as those of the previous embodiment, so here,
In particular, only the differences from the configuration of FIG. 6 will be described.

As shown in FIG. 12, a polarization filter, a polarization selective hologram, and a polarization glass 310 can be used as the annular light shielding filter 3 of this embodiment.

At this time, the laser light emitted from the semiconductor laser 8 is split into three beams of 0th order light and ± 1st order light by the diffraction grating plate 7, and is made into parallel light by the collimator lens 6, and the super resolution filter 240 The side filter and the main lobe are aligned on the track on the disk 1 by the band-shaped filter (a), or the side lobe is generated in an annular shape by the circular filter (b) of the super-resolution filter 240. Then, the polarization beam splitter 5 allows the laser light from the super-resolution filter 240 to pass therethrough and allows the annular light-shielding filter 3 to pass therethrough, and the λ / 4 plate 4 converts the linearly polarized light into circularly polarized light, and the objective lens 2 converts the laser light. To converge. Further, a laser beam having a predetermined focused spot diameter is passed through the objective lens 2,
The circularly polarized light is converted into linearly polarized light by the λ / 4 plate 4, and is totally reflected by the polarization beam splitter 5 through the annular light shielding filter 3,
The light can be collected by the condenser lens group 9 including a spherical lens and received by the photodetector 10.

As described above, the basic operation of this embodiment is the same as that of the embodiment shown in FIG. 6 except that there is a difference in the positions of the annular shading filter 3 and the λ / 4 plate 4. .

The structure corresponding to the claims of the optical reproducing apparatus of the above embodiment has the following features.

In the optical reproducing apparatus of the above embodiment, the annular light-shielding filter 3 as the numerical aperture changing means for changing the numerical aperture according to the disc substrate thickness of the optical recording medium to be reproduced is
With a liquid crystal shutter made of the guest-host type liquid crystal 300 and a ring-shaped liquid crystal shutter made of the guest-host type liquid crystal 300, its numerical aperture can be easily changed. Further, in the case of the annular polarization filter 3 that selectively shields the outer side of the light incident on the objective lens 2, the annular polarization filter 3
Can easily change the numerical aperture. In the case of a ring-shaped polarization-selective hologram that selectively shields the outer side of the light entering the objective lens 2, the numerical aperture can be easily changed by the ring-shaped polarization-selective hologram. Further, in the annular polarizing glass 310 that selectively shields the outer side of the light incident on the objective lens 2, the numerical aperture can be easily changed by the annular polarizing glass 310.

In the optical reproducing apparatus of the above-mentioned embodiment, the disk substrate thickness of the recording medium is 1.1 to 1.3 mm and 0.
In the case of 55 to 0.65 mm, the objective lens 2
By condensing light at a position of 0.7 to 0.9 mm in depth, the condensed light spot size can be appropriately reduced.

In the optical reproducing apparatus of the above-mentioned embodiment, the objective lens 2 is designed so as to focus light at a depth of 0.8 mm, and the disk substrate thickness of the recording medium is 1.1-.
When it is set to 1.3 mm and 0.55 to 0.65 mm, the objective lens 2 can focus light at a depth of 0.8 mm and can minimize the focused spot size.

In the optical reproducing apparatus of the above embodiment, the numerical aperture of the objective lens 2 is 0.43 to 0.47 when reproducing an optical recording medium having a disk substrate thickness of 1.1 to 1.3 mm.
And the numerical aperture of the objective lens 2 when reproducing an optical recording medium having a disk substrate thickness of 0.55 to 0.6 mm is set to 0.
When set to 50 to 0.55, the condensed spot size when reproducing an optical recording medium having a disc substrate thickness of 1.2 mm is about 1.2 μm, and the disc substrate thickness is 0.6.
When reproducing an optical recording medium of mm, the focused spot size is about 1.0 μm, and a standardized optical disk can be sufficiently reproduced.

In the optical reproducing apparatus of the above embodiment, the output of the pickup is input to the correction circuit for changing the reproduction output characteristic according to the recording medium to be reproduced.
The reproduction output characteristic of the output of the pickup is corrected by the correction circuit, and sufficient reproduction is possible even if the condensed spot size is slightly large.

In the optical reproducing apparatus of the above embodiment, the correction circuit has a built-in function of emphasizing the high frequency characteristic and increasing the crosstalk correction amount, and reproduces the optical recording medium having a large reproduction distortion. In this case, the high frequency characteristic is emphasized more and the crosstalk can be removed more greatly.

In the optical reproducing apparatus of the above-mentioned embodiment, since the pickup is provided with the filter for blocking the central portion of the light incident on the objective lens 2,
The super-resolution can reduce the size of the focused spot. Further, in the case where the pickup has an intersymbol interference canceling circuit that switches a circuit constant according to the type of recording medium to be reproduced, it is possible to electrically cancel intersymbol interference caused by utilizing super-resolution. .

[0094]

As described above, in the optical reproducing apparatus according to the first aspect, in a reproducing apparatus for reproducing plural kinds of optical recording media having different disk substrate thicknesses, it is shallower than the thick disk substrate and deeper than the thin disk substrate. For recording media with different disk substrate thicknesses that have a built-in pickup with an objective lens adapted to focus the reproduction beam at a position, it is only necessary to have an objective lens designed with a disk substrate thickness between them. It is possible to set the focused spot size to the recording medium in a well-balanced manner.

In the optical reproducing apparatus of the second aspect, the numerical aperture changing means for changing the numerical aperture according to the thickness of the disk substrate of the optical recording medium reproduced by the objective lens is provided, and in addition to the effect of the first aspect. By changing the numerical aperture,
Furthermore, the focused spot size can be set in a well-balanced manner.

In the optical reproducing apparatus of the third aspect, the numerical aperture is changed so that the focused spot on the recording surface of the optical recording medium reproduced by the numerical aperture changing means becomes small. In addition to the effect of, the focused spot size can be minimized.

In the optical reproducing apparatus of the fourth aspect, the numerical aperture changing means is an annular liquid crystal shutter which selectively blocks the outside of the light incident on the objective lens.
In addition to the effect of claim 2 or claim 3, the numerical aperture can be easily changed by the annular liquid crystal shutter.

In the optical reproducing device of the fifth aspect, since the numerical aperture changing means is a liquid crystal shutter made of a guest-host type liquid crystal, in addition to the effect of the fourth aspect, a liquid crystal shutter made of an annular guest-host type liquid crystal is used. The numerical aperture can be changed easily.

In the optical reproducing apparatus of the sixth aspect, since the numerical aperture changing means is an annular polarization filter which selectively shields the light incident on the objective lens from the outer side,
In addition to the effect of claim 2 or claim 3, the numerical aperture can be easily changed by the annular polarization filter.

In the optical reproducing apparatus of the seventh aspect, the numerical aperture changing means is an annular polarization selective hologram which selectively shields the outer side of the light incident on the objective lens. In addition to the effect of 4, the numerical aperture can be easily changed by the circular polarization selective hologram.

In the optical reproducing device of the eighth aspect, the numerical aperture changing means is an annular polarizing glass that selectively shields the outer side of the light incident on the objective lens.
In addition to the effect of claim 2 or claim 3, the numerical aperture can be easily changed by the annular polarizing glass.

In the optical reproducing apparatus of the ninth aspect, the disk substrate thickness of the recording medium is 1.1 to 1.3 mm and 0.55.
Is about 0.65 mm, and the objective lens has a depth of 0.7 to
Since the light is focused at a position of 0.9 mm, in addition to the effect according to any one of claims 1, 4, 5, and 6 to 8, 1.1 to When the distance is 1.3 mm and 0.55 to 0.65 mm, the condensed spot size can be appropriately reduced by condensing the light at the depth of 0.7 to 0.9 mm by the objective lens.

In the optical reproducing apparatus of the tenth aspect, since the objective lens is focused at a position of 0.8 mm in depth, in addition to the effect of the ninth aspect, the disk substrate thickness is 1. When the distance is 1 to 1.3 mm and 0.55 to 0.65 mm, the focused spot size can be minimized by focusing the light at a depth of 0.8 mm with the objective lens.

In the optical reproducing apparatus of the eleventh aspect, the numerical aperture of the objective lens when reproducing the optical recording medium having the disk substrate thickness of 1.1 to 1.3 mm is set to 0.43 to 0.47, When reproducing an optical recording medium having a disc substrate thickness of 0.55 to 0.6 mm, the numerical aperture of the objective lens is set to 0.50 to 0.50.
Since it is set to 0.55, in addition to the effect of claim 9 or claim 10, the disk substrate thickness is 1.2 mm.
The condensing spot size when reproducing the optical recording medium is about 1.2 μm, and the condensing spot size when reproducing the optical recording medium with the disc substrate thickness of 0.6 mm is about 1.0 μm.
Therefore, the standardized optical disc can be sufficiently reproduced.

In the optical reproducing apparatus of the twelfth aspect, the output of the pickup is inputted to the correction circuit for changing the reproduction output characteristic according to the recording medium to be reproduced, so that any one of the first to eleventh aspects. In addition to the effect described in the above, the reproduction output characteristic of the output of the pickup is corrected by the correction circuit, and sufficient reproduction can be performed even if the condensed spot size is somewhat large.

In the optical reproducing apparatus of the thirteenth aspect, since the correction circuit emphasizes the high frequency characteristic and increases the crosstalk correction amount, in addition to the effect of the twelfth aspect,
When reproducing the optical recording medium in which the reproduction distortion is large, the high frequency characteristic is further emphasized, and the crosstalk can be largely eliminated.

In the optical reproducing apparatus of the fourteenth aspect, the pickup has a filter for blocking the central portion of the light incident on the objective lens. Therefore, the optical reproducing apparatus according to any one of the first to thirteenth aspects. In addition to the above effect, the super-resolution can reduce the size of the focused spot.

Since the optical reproducing apparatus according to the fifteenth aspect has an intersymbol interference canceling circuit for switching the circuit constant according to the type of the recording medium to be reproduced, the optical reproducing apparatus according to any one of the first to fourteenth aspects. In addition to the effects described, it is possible to electrically remove intersymbol interference caused by using super-resolution.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram of an optical reproducing device according to a first embodiment of the present invention.

FIG. 2 is a plan view of an annular shading filter used in the optical reproducing device of the first embodiment of the present invention.

FIG. 3 shows the NA and the focused spot diameter of a 0.8 mm objective lens used in the optical reproducing apparatus according to the first embodiment of the present invention when focused on a 0.6 mm thick disk substrate. It is a characteristic view which shows a relationship.

FIG. 4 shows the NA and the focused spot diameter when the 0.8 mm objective lens used in the optical reproducing apparatus of the first embodiment of the present invention is focused on a 1.2 mm thick disk substrate. It is a characteristic view which shows a relationship.

FIG. 5 is a block diagram of a reproduction control circuit used in the optical reproducing device of the first embodiment of the present invention.

FIG. 6 is an overall configuration diagram of an optical reproducing device according to a second embodiment of the present invention.

FIG. 7 is an explanatory diagram of a band-shaped filter (a) and a circular filter (b) of the super-resolution filter used in the optical reproducing device of the second embodiment of the present invention.

FIG. 8 is a functional explanatory diagram of a band-shaped filter (a) and a circular filter (b) of the super-resolution filter of FIG. 7.

FIG. 9 is a block diagram of a reproduction control circuit used in the optical reproducing device of the second embodiment of the present invention.

FIG. 10 is an explanatory diagram showing the operation principle for explaining the guest-host type liquid crystal that constitutes the annular light-shielding filter used in the optical reproducing device of the first embodiment of the present invention.

FIG. 11 is a schematic diagram illustrating a polarizing glass constituting an annular light shielding filter used in the optical reproducing device of the first embodiment of the present invention.

FIG. 12 is an overall configuration diagram of an optical reproducing device according to a third embodiment of the present invention.

[Explanation of symbols]

 1 Disc 2 Objective Lens 3 Annular Light-Shielding Filter 4 λ / 4 Plate 5 Polarizing Beam Splitter 6 Collimating Lens 7 Diffraction Grating Plate 8 Semiconductor Laser 9 Condensing Lens Group 10 Photodetector 300 Guest Host Liquid Crystal 310 Polarizing Glass

Continuation of front page (72) Inventor Shuichi Ichiura 2-5-5 Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd.

Claims (15)

[Claims] 1. A reproducing apparatus for reproducing a plurality of types of optical recording media having different disk substrate thicknesses, wherein a pickup having an objective lens for condensing a reproducing beam at a position shallower than a thick disk substrate and deeper than a thin disk substrate is provided. An optical playback device characterized by being built-in. 2. The optical reproducing apparatus according to claim 1, wherein the objective lens is provided with a numerical aperture changing means for changing a numerical aperture according to the thickness of the disk substrate of the optical recording medium to be reproduced. . 3. The optical reproducing apparatus according to claim 2, wherein the numerical aperture changing means sets the numerical aperture so that a focused spot on the recording surface of the optical recording medium to be reproduced becomes small. . 4. The numerical aperture changing means is an annular liquid crystal shutter for selectively blocking the outer side of the light incident on the objective lens.
The optical reproducing device according to item 1. 5. The optical reproducing apparatus according to claim 4, wherein the numerical aperture changing unit is a liquid crystal shutter made of guest-host type liquid crystal. 6. The optical apparatus according to claim 2, wherein the numerical aperture changing unit is an annular polarization filter that selectively shields the light incident on the objective lens from the outer side. Playback device. 7. The numerical aperture changing means is an annular polarization-selective hologram that selectively shields the outer side of the light incident on the objective lens. The optical reproduction device described. 8. The numerical aperture changing means is an annular polarizing glass that selectively shields the outer side of the light incident on the objective lens, as claimed in claim 2 or 3. Optical playback device. 9. The disk substrate thickness of the plurality of types of optical recording media is 1.1 to 1.3 mm and 0.55 to 0.65 m.
m, and the objective lens is focused at a position of 0.7 to 0.9 mm in depth, any one of claim 1, claim 4, claim 5, and claim 6 to claim 8. The optical reproducing device according to any one of the above. 10. The optical reproducing apparatus according to claim 9, wherein the objective lens is focused at a position having a depth of 0.8 mm. 11. The disk substrate has a thickness of 1.1 to 1.
When reproducing a 3 mm optical recording medium, the numerical aperture of the objective lens is set to 0.43 to 0.47, and the disc substrate thickness is 0.5.
The optical reproducing device according to claim 9 or 10, wherein the numerical aperture of the objective lens when reproducing an optical recording medium of 5 to 0.6 mm is set to 0.50 to 0.55. 12. The output of the pickup is input to a correction circuit that changes a reproduction output characteristic according to a recording medium to be reproduced, according to any one of claims 1 to 11. Optical playback device. 13. The correction circuit emphasizes high frequency characteristics,
The optical reproducing device according to claim 12, wherein the crosstalk correction amount is increased. 14. The optical reproducing apparatus according to claim 1, wherein the pickup includes a filter that blocks a central portion of light incident on the objective lens. 15. The optical apparatus according to claim 1, wherein the pickup has an inter-symbol interference canceling circuit that switches a circuit constant according to a type of a recording medium to be reproduced. Playback device.