JPH09134541A - Optical pick-up device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve miniaturization and low costs by providing a transmittance changing element in an optical path between a light source and a reflection type optical recording medium to obtain reproduction compatibility between mediums having a different base board thickness of CD, CVD or the like with simpler structure. SOLUTION: An objective lens 4 converges a reproducing light beam from a light source 1 on a medium 5, and a detector not illustrated detects a reproducing light beam including an information signal from the medium 5. A transmittance changing element 3 is provided in an optical path for a reproducing light beam between the light source 1 and the medium 5, and a transmittance for the reproducing light beam is changed in response to at least one of light intensity and temperature. Therefore, the substantial number of openings (NA) can be changed by changing the intensity of the reproducing light beam. Accordingly, reproduction compatibility can be obtained for a disk having a different base board thickness with simple structure without providing two objective lenses having a different NA unlike the conventional one nor providing an aperture and without using mechanical structure at all.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the structure of an optical pickup device for reproducing an optical recording medium.

[0002]

2. Description of the Related Art A digital video disc (DVD) capable of recording a moving image such as a movie on a compact disc having a diameter of 120 mm for two hours or more has been actively developed.
1.2mm thickness for conventional compact discs (CDs)
Although a transparent substrate such as polycarbonate is used,
As such a DVD, a DVD having a structure in which transparent substrates such as polycarbonate having a thickness of 0.6 mm are bonded is proposed.

If such an optical pickup device for DVD is also used for a conventional optical pickup device for CD, the thickness of the substrate, that is, the distance from the substrate surface to the recording layer is different, so that the influence of aberration is exerted. It becomes large, and it becomes difficult to obtain a good light spot for both substrates. For this reason, in order to reproduce both the conventional CD and the DVD having a thin substrate, the pickup device needs a special device.

As a method of solving such a problem, the pickup itself has two objective lenses corresponding to a thick substrate and a thin substrate, that is, a thick substrate has a low NA (numerical aperture) lens and a thin substrate. High NA for substrate
A method has been proposed in which (numerical aperture) lenses are provided and these lenses are mechanically switched according to the substrate.

Further, only a single objective lens corresponding to a thin substrate is provided, and when reproducing a disc on a thick substrate, an aperture is inserted in the optical path to achieve a substantial NA.
A method of lowering is also proposed. With such a system, it is possible to reproduce a high-density disc of a thin substrate having a thickness of 0.6 mm and a conventional CD having a thickness of 1.2 mm, and it is possible to achieve reproduction compatibility.

[0006]

However, in the method of switching the lens, it is necessary to provide two objective lenses inside the pickup and a mechanism for switching the lens is required, which makes it difficult to reduce the size and cost. There was a problem.

Further, the method of inserting the aperture in the optical path can have a simpler structure than the method of switching the lens described above, but it also requires a mechanical mechanism for inserting the aperture in the optical path. However, there is a problem that it is difficult to reduce cost and size.

The object of the present invention is to achieve reproduction compatibility between media having different distances from the surface on the reproduction light incident side to the recording surface with a simpler structure, and therefore, cost reduction and size reduction are possible. To provide a simple optical pickup device.

[0009]

SUMMARY OF THE INVENTION The present invention is an optical pickup device for irradiating a reflective optical recording medium with reproducing light output from a light source, detecting the reflected light and reproducing the information recorded on the medium. In the forward light path between the light source and the reflection type optical recording medium, there is provided means for changing the transmittance in accordance with at least one of the light intensity of the reproduction light and the temperature rise due to the reproduction light.

An optical pickup device according to a preferred aspect of the present invention is an optical pickup device which emits reproduction light for reproducing information recorded on a medium and detects reproduction light containing an information signal from the medium. Between the light source for emitting the reproduction light, the means for condensing the beam of the reproduction light from the light source on the medium, the means for detecting the reproduction light containing the information signal from the medium, and the light source and the medium. And an element that is provided in the forward path of the reproduction light and whose transmittance with respect to the reproduction light changes according to at least one of the light intensity and the temperature.

In the present invention, the means or element for changing the transmittance is preferably provided in the light source device. An element whose transmittance for reproducing light changes depending on at least one of light intensity and temperature (hereinafter referred to as “transmissivity changing element”) is, for example, a photon mode reaction or a thermal reaction, in which a part of the molecular structure is changed. It can be formed using a dye material whose absorbance changes. Examples of such a material include a reverse photochromic light absorber, a saturable light absorber, and a thermochromic light absorber.

The reverse photochromic light absorber has absorption in the wavelength range of reproduction light at room temperature, and when exposed to light, a photon mode causes a decoloring reaction, and at the same time, a thermal reaction at room temperature causes a coloring reaction. It is such a material. Examples of such a material include spiropyran-based materials and spirooxazine-based materials dispersed in a polar polymer.

The saturable absorptive light absorber is a light absorber in which the absorption coefficient decreases and the amount of absorbed light saturates when the light intensity increases. For example, bis (tri-n-hexylsiloxy) silicon Examples include phthalocyanine.

The thermochromic light absorber is a light absorber in which a color erasing reaction occurs when the temperature rises. For example, a fluoran compound is mixed with gallic acid propyl ester, trimethylolethane and diacetone alcohol, dissolved and dried. The thermochromic composition obtained by doing so is mentioned.

The transmittance changing element in the present invention can be formed from a thin film or a molded body containing the above-mentioned light absorber. Such a thin film or molded body can be formed from a polymer containing a light absorber. In the case of a thin film, a thin film may be formed by vapor-depositing a light absorber. Further, such a thin film may be provided on a transparent support and held by a holder. Also,
The transmittance changing element may be incorporated in the optical element in the optical path of the reproduction light between the light source and the medium. That is, a thin film that serves as a transmittance changing element may be provided on the surface of such an optical element. Further, when the optical element is made of plastic or the like, the optical element itself may contain the above-mentioned material of the light absorber to impart the function of the transmittance changing element to the optical element.

A semiconductor laser can be generally used as a light source for emitting the reproduction light. The wavelength of the semiconductor laser is not particularly limited, but it is expected that red semiconductor lasers having wavelengths of 650 nm and 635 nm, which are being used in recent years, and higher density recording will be possible in the future. A blue semiconductor laser or the like can also be used.

The means for condensing the reproduction light beam on the medium is not particularly limited, but an objective lens or the like is generally used. FIG. 1 is a schematic diagram for explaining the principle of the present invention. With reference to FIG. 1, radiated light emitted from a semiconductor laser 1 which is a light source is shaped by a collimator lens 2, passes through a transmittance changing element 3, enters an objective lens 4, and is condensed on a disk 5. It

Usually, the light emitted from the semiconductor laser has a light intensity distribution in which the intensity of the central portion is high and the intensity of the peripheral portion is weak. FIG. 2C shows the light intensity distribution of the laser beam used as such reproduction light. A laser beam having such a light intensity distribution,
When the transmittance changing element, which is set so that the transmittance of the reproduced light becomes higher as the light intensity becomes higher, when the total intensity of the beam is relatively weak, as shown in FIG. The transmittance is improved. Further, when the total intensity of the beam is relatively strong, as shown in FIG.
The transmittance is improved not only in the central portion but also in the peripheral portion.

FIG. 3 is a plan view showing the transmittance changing state of the transmittance changing element when the total intensity of the beam is changed. In FIG. 3, a hatched portion indicates a low transmittance region, and a white portion inside the hatched region indicates a high transmittance region. FIG. 3A corresponds to the state of FIG. 2A and shows a state where the transmittance is high not only in the central portion but also in the peripheral portion when the total intensity of the beam is high. FIG. 3 (b)
2B corresponds to FIG. 2B, and shows a state in which the transmittance is improved only in the central portion and is low in the peripheral portion when the total intensity of the beam is weak.

As shown in FIG. 3, by changing the total intensity of the beam, it is possible to control the area of the region having high transmittance of the transmittance changing element. As shown in FIG. 3A, when the area of the region 3a having a high transmittance is increased, a state similar to that of a substantially high numerical aperture (NA) can be obtained. Further, as shown in FIG. 3B, by reducing the area of the region 3a having a high transmittance, a state similar to that of a substantially low numerical aperture (NA) can be obtained. Therefore, the substantial numerical aperture can be changed by changing the intensity of the reproducing light beam. Therefore, it is possible to provide a pickup device having reproduction compatibility with disks having different substrate thicknesses with an extremely simple structure without using any mechanical mechanism.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION An element using an inverse photochromic dye was manufactured as a transmittance changing element. Inverse photochromic dyes usually have absorption in a wavelength range used as reproduction light at room temperature, and when exposed to light, a photon mode causes a decoloring reaction, and at the same time, a thermal reaction at room temperature also causes a coloring reaction. . Therefore, in the transmittance changing element using the inverse photochromic dye, the light transmittance is high when the light intensity is high, and the light transmittance is low when the light intensity is low. In particular, this change in transmittance is desirable because it increases non-linearly, that is, has a threshold value, as the initial optical density is increased.

As the reverse photochromic material, spiroselenazolinobenzopyran can be used, and this can be dispersed in a polymer having high polarity and molded into an optical element. In this embodiment, mixed with polymethacrylic acid,
This was dissolved in dichloromethane, put in a predetermined mold, and the solvent was evaporated to form an optical element. Various optical densities from 0.2 to 2.0 were prepared. The optical density is defined by the material density (mol / l), the element thickness (cm), and the molecular extinction coefficient (l / (mol · cm)) of the material at the reproduction light wavelength. Therefore, it can be adjusted by changing the concentration of the reverse photochromic material or changing the thickness of the optical element.

First, the relationship between the laser power and the spot diameter was examined using a transmittance changing element having an optical density of 0.8. In the installed state as shown in FIG. 1, that is, the transmittance changing element 3 was installed on the front side of the objective lens 4, and as the semiconductor laser 1, a semiconductor laser having a wavelength of 650 nm was used. The objective lens 4 has a numerical aperture (N
The one in which A) was 0.6 was used. It has a thickness of 0.6
It has a numerical aperture corresponding to a substrate of mm. The laser power of the laser light emitted from the semiconductor laser 1 was changed, and the spot diameter focused on the disk 5 was measured.

FIG. 4 is a diagram showing the relationship between the laser power measured in this way and the spot diameter. As shown in FIG. 4, when the laser power is 1 mW, the spot diameter is about 1.6 μm which is the spot diameter used in the conventional reflective CD, but the spot diameter becomes smaller as the power is increased. With a laser power of 3 mW, the spot diameter is about 0.8 μm which is the spot diameter used for the high density reflection type CD. Therefore, by changing the laser power,
It can be seen that the spot diameter can be controlled.

Next, a conventional CD and a high density CD were reproduced by using a transmittance changing element with a reproducing apparatus having a structure as shown in FIG. Referring to FIG. 5, a beam splitter 6 is provided between the objective lens 4 and the transmittance changing element 3, and the disk 5
The reproduction light reflected from the detector is sent to the detector 7. The detector 7 detects a reproduction signal and also detects a focus error signal and a tracking error signal. As the semiconductor laser 1, the collimator lens 2, the transmittance changing element 3, and the objective lens 4, the same ones as those of the above-described embodiment described with reference to FIG. 1 were used.

As the disk 5, a conventional CD type disk, a polycarbonate substrate (thickness 1.2 mm)
The shortest pit (3T signal) of 0.8 μm and the track pitch of 1.6 μm was used. Therefore, in the conventional reflective CD, the distance from the medium surface on the reproducing light incident side to the reflective recording layer surface is 1.2 mm. Also high density C
As the D type, a polycarbonate substrate (thickness 0.6 mm), a shortest pit (3T signal) 0.42 μm, and a track pitch 0.8 μm was used. Therefore, in the high density reflection type CD, the distance from the medium surface on the reproduction light incident side to the reflection type recording layer surface is 0.6 mm. The astigmatism method was used for the focus servo, and the differential push-pull method was used for the tracking servo. As the transmittance changing element 3, various elements were used whose optical density was adjusted to 0.2 to 2.0 by increasing the concentration of the inverse photochromic material or increasing the thickness of the optical element.

EFM signals of the above-mentioned conventional CD and high density CD were reproduced by using the transmittance changing elements with reproduction powers of 1 mW and 3 mW and various optical densities. When a high density CD is reproduced with a reproduction power of 3 mW, it does not depend on the optical density of the transmittance changing element,
Good reproduction output was obtained in all the transmittance changing elements. On the other hand, when the conventional CD was reproduced with the reproduction power of 1 mW, the quality of the reproduced signal depended on the optical density of the transmittance changing element.

FIG. 6 is a diagram showing the jitter value of the 3T signal at the time of double speed reproduction. As shown in FIG. 6, the higher the optical density of the transmittance changing element, the smaller the jitter value. In particular, when the optical density becomes 0.8 or more, the jitter value becomes close to 0.8 ns, and it can be seen that a good reproduction signal can be obtained.

FIG. 7 is a schematic view showing another embodiment of the optical pickup device according to the present invention. Referring to FIG.
The reproduction light emitted from the semiconductor laser 11, which is the light source, is sent to the three-division diffraction grating 12 that divides the beam into three for tracking servo. The reproduction light divided into three is sent to a hologram 13 as a beam splitter which gives astigmatism due to focus servo, and is condensed on a disk 15 through an objective lens 14. The reproduction light reflected from the disk 15 passes through the objective lens 14 again, is diffracted by the hologram 13, and is sent to the detector 16. The detector 16 is a 6-division photodetector, which detects a reproduction signal and a focus servo control signal and a tracking servo control signal.

In the present embodiment, in such an optical pickup system, the transmittance changing element 17 of the present invention is formed as a thin film on the light incident side of the three-division diffraction grating 12.
Therefore, the transmittance changing element 17 is formed integrally with the three-division diffraction grating 12.

In the present embodiment, the transmittance changing element may be integrally formed on the surface of the hologram 13 or the objective lens 14, but the hologram 13 and the objective lens 1 may be formed.
In FIG. 4, since the reproduction light is already divided into three, when the beam is divided into three and the function of the transmittance changing element is adversely affected, as in the embodiment shown in FIG. It is preferably provided on the light incident side of the three-division diffraction grating 12. Further, as a matter of course, the transmittance changing element may be formed as an independent optical element and provided at a position on the forward optical path between the semiconductor laser 11 and the disk 15.

Further, a transmittance changing element may be provided at the light emitting portion of the semiconductor laser 11 which is the light source. FIG.
FIG. 6 is a cross-sectional view showing a semiconductor laser device (light source device) in which the transmittance changing element is provided in the light emitting portion of the laser as described above. Referring to FIG. 8, the block 2 is provided on the stem 21.
2 is provided, and the heat sink 23 is provided on the block 22.
The semiconductor laser element 24 is attached via. A cap 26 is provided around these, and a flat glass 27 or a diffraction grating or the like is attached to a window portion formed in the cap 26. A lead terminal 25 extends from the stem 21.

The transmittance changing element 28 of the present invention is formed as a thin film on the flat glass plate 27. It may also be formed as a thin film below the flat glass 27. Therefore, the light emitted from the semiconductor laser element 24 is emitted through the transmittance changing element 28. The light emitted from the semiconductor laser element 24 is emitted in a state having the above-mentioned light intensity distribution, and therefore, by controlling the light intensity of the laser light, the light is transmitted through the transmittance changing element 28 as described above. It is possible to control the area having a high rate. When the transmittance changing element is provided in the vicinity of the light emitting end face of the semiconductor laser as described above, since the intensity of the laser light is high, a sufficient effect can be easily obtained even if a semiconductor laser having relatively poor output characteristics is used. .

FIG. 9 is a schematic diagram showing still another embodiment of the optical pickup device according to the present invention. In this embodiment, a three-division diffraction grating that divides the laser light from the light source 11 into three is provided as a reflection-type three-division diffraction grating. The light emitted from the semiconductor laser 11 is reflected by the three-division diffraction grating 12 in the state of being divided into three, passes through the hologram 13 and the objective lens 14, and is irradiated onto the disk 15. The reflected light from the disk 15 is diffracted by the hologram 13 and sent to the detector 16.

In this embodiment, the reflection type three-division diffraction grating 12 is used, and such three-division diffraction grating 12 is used.
Although the transmittance changing element of the present invention may be formed on the uneven surface of, it is generally difficult to make the film thickness uniform, so that the window on the emission side of the light source as shown in FIG. It is preferable to provide a transmittance changing element. If there is no adverse effect of dividing the laser light into three, the hologram 1
3, or a transmittance changing element may be provided integrally with the objective lens 14. A transmittance changing element may be provided as an independent component.

In the above embodiment, the transmittance changing element using the reverse photochromic light absorber has been described as an example, but the present invention is not limited to this, and the saturable light absorber. Alternatively, a transmittance changing element using a thermochromic light absorber can be used.

Further, as described above, the transmittance changing element may be provided integrally with an optical element such as an objective lens, a collimating lens, a beam splitter or the like, or may be provided as an independent optical element. Further, in the case of an optical element made of plastic, it is possible to include the above-mentioned materials in the optical element itself so that the optical element itself has the function of the transmittance changing element. In particular, the plastic objective lens itself may have this function.

[0038]

According to the present invention, reproduction compatibility between media having different substrates can be achieved with a simpler structure.
Therefore, an optical pickup device having reproduction compatibility can be manufactured at low cost and in a smaller size.

[Brief description of the drawings]

FIG. 1 is a schematic diagram for explaining the principle of the present invention.

FIG. 2 is a diagram showing a transmittance state of a transmittance changing element due to a difference in beam intensity of reproduction light.

FIG. 3 is a plan view showing a region having a high transmittance and a region having a low transmittance of a transmittance changing element due to a difference in beam intensity of reproduction light.

FIG. 4 is a diagram showing a relationship between laser power and spot diameter in the embodiment according to the present invention.

FIG. 5 is a configuration diagram showing an optical pickup device of an embodiment according to the present invention.

FIG. 6 is a diagram showing the relationship between the optical density of the transmittance changing element and the jitter value of a 3T signal during double-speed reproduction according to an embodiment of the present invention.

FIG. 7 is a schematic diagram showing a configuration of an optical pickup device of another embodiment according to the present invention.

FIG. 8 is a cross-sectional view showing a laser semiconductor element in which a transmittance changing element according to still another embodiment of the present invention is integrated.

FIG. 9 is a schematic diagram showing the configuration of an optical pickup device of still another embodiment according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Semiconductor laser 2 ... Collimating lens 3 ... Transmittance changing element 3a ... Area | region with high transmittance in transmittance changing element 3b ... Area with low transmittance in transmittance changing element 4 ... Objective lens 5 ... Disk 6 ... Beam splitter 7 ... detector 11 ... semiconductor laser 12 ... three-division diffraction grating 13 ... hologram 14 ... objective lens 15 ... disk 16 ... detector 17 ... transmittance changing element

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Masahiro Irie 1-29 Kasuga Park Kasuga City Fukuoka Prefecture

Claims (8)

[Claims] 1. An optical pickup device for irradiating a reflection type optical recording medium with reproduction light output from a light source and detecting the reflected light to reproduce information recorded on the medium, wherein the light source and the reflection type An optical pickup device comprising a means for changing the transmittance in the forward light path between optical recording media in accordance with at least one of the light intensity of the reproduction light and the temperature rise due to the reproduction light. 2. An optical pickup device for irradiating reproduction light for reproducing information recorded on a medium and detecting reproduction light containing an information signal from the medium, wherein the light source emits the reproduction light. Means for condensing a beam of reproduction light from the light source on the medium, means for detecting reproduction light containing an information signal from the medium, the means between the light source and the medium An optical pickup device comprising: an element which is provided in a forward path of reproduction light and whose transmittance for the reproduction light is changed according to at least one of light intensity and temperature. 3. The light source device is provided with means or an element for changing the transmittance.
An optical pickup device according to item 1. 4. The optical pickup device according to claim 1, wherein the element whose transmittance changes includes an optical absorber having an inverse photochromic property. 5. The optical pickup device according to claim 1, wherein the element whose transmittance changes includes a saturable absorber. 6. The optical pickup according to claim 1, wherein the element of which the transmittance changes is an element of which the transmittance increases non-linearly according to at least one of light intensity and temperature. apparatus. 7. The element in which the transmittance changes includes a light absorber so that the optical density becomes 0.8 or more.
The optical pickup device according to any one of 1. 8. The optical pickup device according to claim 1, wherein the light source is a semiconductor laser.