JPH0863776A - Optical head, optical disk and optical disk device - Google Patents

Abstract

PURPOSE: To provide an optical disk device efficiently reproducing recording signal information stored in an optical disk as a phase change, to improve the regenerative signal characteristic of the optical disk and to record information with high density. CONSTITUTION: A reflected beam 20 from the optical disk is separated into a component incident on a phase conjugate mirror temporarily and the component incident on a regular reflection mirror 3. The reflected beams from both mirrors are synthesized through a beam splitter 1 to be made incident on a signal detector 4. Since a phase of incident light and the phase of outgoing light are in an inversive relation in the phase conjugate mirror 2, the phase change component of the beam after being synthesized by the beam splitter 1 becomes double of the incident light. Thus, the phase change is emphasized, and when a phase information change is reproduced, this reproducing method is effective largely, and the synthesized beam increases the phase information of the reflected beam from the optical disk to double, and an excellent regenerative signal is obtained even when the phase change in the optical disk is small.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disk device, and more particularly to an optical head, an optical disk and an optical disk device for reproducing information recorded at high density by using a laser beam.

[0002]

2. Description of the Related Art An optical disk recording system using a laser beam is capable of performing large-capacity recording and non-contact high-speed access. Optical discs are classified into a read-only type known as a compact disc and a laser disc, a write-once type that can be recorded by the user himself, and a rewritable type that can be repeatedly recorded and erased by the user. Write-once and rewritable optical discs are
Used as an external memory of the data or a document / image file.

[0003] As rewritable optical disks, there are a phase change optical disk using a phase change of a recording film and a magneto-optical disk using a change in the magnetization direction of a perpendicular magnetization film. Of these, phase-change optical disks are expected to become the mainstream of rewritable optical disks in the future because they do not require an external magnetic field and can be easily overwritten.

A rewritable, so-called phase-change type optical disk using a recording film which undergoes a phase change between crystal and amorphous by irradiation with laser light has been conventionally known. In a phase-change type optical disc, a high power level corresponding to the information to be recorded on the recording film.
The light spot is irradiated to locally raise the temperature of the recording film to cause a phase change between the crystal and the amorphous for recording, and the change in the optical constants accompanying the change is recorded with a laser light of low power. Playback is performed by reading as the reflected light intensity difference.

In an optical disc using a recording film capable of high-speed crystallization, a single laser beam condensed in a circle is used. Conventionally known methods perform crystallization or amorphization by changing the power of laser light between two levels. That is, by irradiating the recording film with laser light having a power capable of raising the temperature of the recording film to a temperature equal to or higher than the melting point, most of the recording film becomes in an amorphous state upon cooling, while the recording film temperature decreases. The portion of the laser beam irradiated with the power so as to reach a temperature higher than the crystallization temperature and lower than the melting point becomes a crystalline state. The recording film of the phase-change optical disk is made of a chalcogenide-based material, such as GeSbTe-based or InSbT-based.
e-based, InSe-based, InTe-based, AsTeGe-based, Te
Ox-GeSn system, TeSeSn system, SbSeBi system,
A BiSeGe system or the like is used, and all are formed by a film forming method such as a resistance heating vacuum evaporation method, an electron beam vacuum evaporation method, and a sputtering method. The state of the recording film immediately after film formation is a kind of amorphous state, and an initialization process in which the entire recording film is made crystalline in order to perform recording on this recording film to form an amorphous recording portion. Is done. Recording is accomplished by forming an amorphous portion within this crystallized state.

Conventionally, a method of utilizing a difference in reflectance between an amorphous recording mark formed on a recording film and a crystal structure formed around the amorphous recording mark has been adopted for reproduction of a phase change type optical disk. An optical head similar to that of a write-once optical disc is used for recording / reproducing on / from a phase change optical disc. Edited by Engineering Society, published by Ohmsha, p
An optical disk device equipped with an optical head similar to the optical head described in 155) is used.

An optical head mounted on the conventional optical disk device will be described with reference to the drawings.

FIG. 4 is a block diagram of a conventional optical head.

The optical head of this conventional example has a laser light source 5
, Shaping prism 11, beam splitter 8, 1 /
The four-wave plate 12 includes a condenser lens 7 mounted on the actuator 6, a signal detection system 13, and a servo signal detection system 9.

After the light emitted from the laser light source 5 is shaped into a circle, the light is condensed by the condenser lens 7 almost to the vicinity of the diffraction limit. The change in the reflectivity of the optical disc 100 is the change in the amount of light reflected from the optical disc 100 as it is. Therefore, the change in the amount of light received by the photodiode of the signal detection system 13 results in a reproduced signal.

[0011]

The above-mentioned conventional phase-change type optical disk is reproduced by utilizing a difference in reflectance between an amorphous recording mark formed on a recording film and a crystal structure formed around the recording mark. Was adopted. Also in designing a disk configuration, attention has been paid to the reflectance difference between the amorphous portion and the crystal portion, and the film thickness and the like have been optimized so as to increase the difference in reflectance.

However, when the difference in reflectance is increased, the difference in absorptivity between the two phases is increased. for that reason,
When overwriting is performed with a single beam, the recording mark length fluctuates due to the difference in the absorptance between the recording mark and the erased portion, so-called jitter occurs, and the reproduction signal quality deteriorates.

In order to suppress the increase in jitter, a method is used in which the difference in the reflectance between the recording mark and the erased portion is made uniform to reduce the difference in the absorptance, and the phase difference between the reflected light from the recording mark and the erased portion is increased. Has been proposed. Using this method, the increase in jitter due to overwriting can be significantly reduced. However, the conventional reproduction method for detecting a change in reflected light cannot effectively extract a reproduction signal component based on a phase difference, and has a disadvantage that the reproduction signal level is reduced.

[0014]

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned drawbacks, to efficiently reproduce information recorded as a phase difference by a simple optical system, and to reduce the jitter of a reproduced signal of a phase change optical disk. It is an object of the present invention to provide an optical disk device that can improve characteristics and obtain good reproduction information.

Therefore, the optical head of the present invention is an optical head for an optical disk which reproduces the phase information of the recording film by irradiating the laser light, and at least a laser light source, a beam splitter, a condenser lens, and a phase. It has a conjugate mirror, a reflecting mirror, and a signal detector, and the reflected light from the optical disc is
The beam splitter separates the component that enters the phase conjugate mirror and the component that enters the reflecting mirror, and the reflected light from the phase conjugate mirror and the reflecting mirror is combined by the beam splitter and enters the signal detector. It is equipped with an optical head that is characterized in that it also uses CdS as a phase conjugate mirror.
_x Se _1-x colored glass filter, or
It is characterized by using Bi ₁₂ SiO ₂₀ and KNbO ₃ .

The optical disk of the present invention uses a phase change recording material for recording / reproducing information by a phase change between crystalline and amorphous as a recording film, and the recording film becomes crystalline and amorphous at a used laser wavelength. At this time, there is a phase difference in the reflected light for both phases.

The optical disk device of the present invention is an optical disk device for recording / reproducing information by changing the state of the recording film due to laser light irradiation, and detects the recorded information formed on the optical disk as a phase change of the reproducing light. It is characterized by doing.

[0018]

[Operation] In the optical system of the optical head that detects the phase information,
A phase conjugate mirror for doubling the phase information is provided to increase the phase difference information of the reproduction light. As a result, a good reproduction signal can be obtained even when the phase change at the recording mark is small.

The configuration of the optical disk device according to the present invention is characterized in that a phase conjugate mirror is provided in the optical path of the optical head of the conventional optical disk device.

FIG. 2 is a diagram for explaining the principle of signal reproduction of the optical disk device according to the present invention.

In FIG. 2, the reflected light 2 from the optical disk is shown.
The 0 is separated by the beam splitter 1 into a component that once enters the phase conjugate mirror 2 and a component that enters the normal reflecting mirror 3. The reflected lights from both are combined via the beam splitter 1 and are incident on the signal detector 4. In the phase conjugate mirror 2, the phase of the incident light and the phase of the emitted light have an inversion relation. Therefore, in the light after being combined by the beam splitter 1, the phase change component is twice the incident light. As a result, the phase change is emphasized, and when the phase information change is reproduced, the effect of the reproducing method of the present apparatus is large. That is, the reflected light (light incident on the detector 4) combined by the optical system of FIG. 2 is obtained by doubling the phase information of the reflected light from the optical disc, and when the phase change on the optical disc is small. Even by using the optical disk device according to the present invention, a good reproduction signal can be secured.

[0022]

Embodiments of the present invention will now be described with reference to the drawings.

First, a first embodiment will be described.

FIG. 1 is a block diagram of an optical head for explaining an embodiment of the present invention.

The optical head of this embodiment has a laser light source 5
A beam splitter 1, a condenser lens 7 mounted on an actuator 6, a phase conjugate mirror 2, a reflecting mirror 3, a photodetector 4, a beam splitter 8, a servo signal detection system 9, and a beam splitter. 10 and an optical disc 100, the parallel laser light emitted from the laser light source 5 is condensed on the optical disc 100 via the condenser lens 7, and the reflected light from the optical disc 100 is condensed. It enters the beam splitter 1 via the lens 7. Here, the laser beam is separated by the beam splitter 1 into a component that is once incident on the phase conjugate mirror 2 and a component that is incident on the ordinary reflecting mirror 3. The reflected lights from both are combined via the beam splitter 1 and are incident on the signal detector 4.

As the laser light source 5, a semiconductor laser having a wavelength of 830 nm and an output of 40 mW was used. The condenser lens 7 having a numerical aperture of 0.55 was mounted on the servo actuator 6. The phase conjugate mirror, using color glass filters CdS _x Se _1-x by degenerate four-wave mixing.

Subsequently, the disk configuration shown in FIG. 3 was determined so that the disk 100 had been formed so that the reflectance difference between the crystal and the amorphous phase was small and the phase difference was large at the wavelength of 830 nm. . The substrate 101 has a diameter of 130 mm,
A polycarbonate substrate with a pre-groove having a thickness of 1.2 mm was used. First protective film 102 and second protective film 104
Is a ZnS + SiO ₂ mixed film, and the recording film 103 is Ge
SbTe was continuously formed by magnetron sputtering using Al for the reflective film 105. The thickness of each layer is 180 nm for the first protective film, 10 nm for the recording film, and 60 n for the second protective film.
m and the reflection film was 50 nm.

In this disc, the difference in reflectance between the amorphous recording mark and the crystalline erased portion at a wavelength of 830 nm was 2%, and the phase difference was 75 °.

Next, using the optical head according to the present invention, overwriting was performed on the disk, and reproduction signal characteristics were evaluated.

After the initialization process, the disk is rotated at 3600 rpm.
8.4 rpm on a 30mm radius track
After recording the signal of MHz (Duty 50%), the signal of 2.2 MHz (Duty 50%) was overwritten on the same track. 13m for recording power and erasing power respectively
W, 7 mW. Next, when this track was reproduced, it was confirmed that a good reproduced signal could be obtained.

Next, a second embodiment will be described.

In the second embodiment, an optical disk device having the same optical system as in the first embodiment and using Bi ₁₂ SiO ₂₀ as a phase conjugate mirror is used to form an optical disk similar to that in the first embodiment. It was confirmed that a good reproduction signal was obtained when signal reproduction was attempted using the above.

Next, a third embodiment will be described.

In the third embodiment, the same optical system as that of the first embodiment is used, and the same optical disk as that of the first embodiment is used by an optical disk device using KNbO ₃ as a phase conjugate mirror. When signal reproduction was attempted, it was confirmed that a good reproduced signal could be obtained.

Next, a fourth embodiment will be described.

In the fourth embodiment, the disk configuration shown in FIG. 3 is determined so that the reflectance difference between the crystal and the amorphous is small and the phase difference is large at a wavelength of 690 nm. Created a disc. The substrate has a diameter of 130 mm,
A polycarbonate substrate with a pre-groove having a thickness of 1.2 mm was used. A ZnS + SiO ₂ mixed film was used for the protective film, GeSbTe was used for the recording film, and Al was used for the reflective film, and the films were continuously formed by magnetron sputtering. The thickness of each layer is 200 nm for the first protective film, 10 nm for the recording film, and 2 for the second protective film.
The thickness was 0 nm and the reflection film was 60 nm.

In this disc, the difference in reflectance between the amorphous recording mark and the crystalline erased portion at a wavelength of 690 nm was 1%, and the phase difference was 70 °.

Next, using the optical head according to the present invention, overwriting was performed on the disk, and reproduction signal characteristics were evaluated.

The number of revolutions of the initialized disc is 3000
Rotate at rpm, 2.9 on track with radius 30mm
After recording the signal of MHz (Duty 50%), the signal of 1.8 MHz (Duty 50%) was overwritten on the same track. Recording power and erasing power 11m each
W, 6 mW. Next, this track was reproduced by an optical disk device according to the present invention, that is, an optical disk device equipped with an optical head using a CdS _x Se _1-x colored glass filter by degenerate four-wave mixing in a phase conjugate mirror. It was confirmed that a reproduction signal could be obtained.

[0040]

As described above, in the optical head, the optical disc and the optical disc apparatus of the present invention, the phase information recorded on the disc can be efficiently reproduced by using the simple optical system using the phase conjugate mirror. By using the phase conjugate mirror, even a small phase change can be detected, and the degree of freedom in disc design can be increased.

Further, in the optical head, the optical disk and the optical disk apparatus of the present invention, the phase difference reproduction itself can provide a reproduction method suitable for the mark edge recording method for recording information at the end of the recording mark, and high density recording is possible. Has the effect of being

[Brief description of drawings]

FIG. 1 is a configuration diagram of an optical head for explaining an embodiment of the present invention.

FIG. 2 is a diagram for explaining a signal reproduction principle of the optical disk device according to the present invention.

FIG. 3 is a configuration diagram of an optical disc for explaining an embodiment of the present invention.

FIG. 4 is a configuration diagram of an optical head mounted in a conventional optical disc device.

[Explanation of symbols]

 1 Beam Splitter 2 Phase Conjugate Mirror 3 Reflector 4 Photo Detector 5 Laser Light Source 6 Actuator 7 Condensing Lens 8 Beam Splitter 9 Servo Signal Detection System 10 Beam Splitter 11 Shaping Prism 12 1/4 Wave Plate 13 Signal Detection System 20 Reflected Light 100 Optical Disc 101 Substrate 102 First Protective Film 103 Recording Film 104 Second Protective Film 105 Reflective Film

Claims (8)

[Claims] 1. An optical head for recording / reproducing / erasing information by changing the state of a recording film of an optical disc by laser light irradiation, wherein recorded information formed on the recording film of the optical disc is used as a phase change of the reproducing light. An optical head characterized by detecting. 2. A recording film made of a phase-change recording material that records and reproduces and erases information by a phase change between crystalline and amorphous, and when the recording film becomes crystalline and amorphous at a used laser wavelength, An optical disk characterized in that the reflected light with respect to the phase has a phase difference. 3. An optical disk device comprising the optical head according to claim 1 and the optical disk according to claim 2. 4. A laser light source, a first beam splitter that splits the beam from the laser light source, a second beam splitter that splits the laser light from the first beam splitter, and the second beam. A third beam splitter for splitting the laser light from the splitter, a condenser lens for condensing the laser light from the first beam splitter, and a reflected light from the optical disc for the first beam splitter, a second A beam splitter, a signal detector for detecting the beam separated by the third beam splitter, a phase conjugate mirror for reflecting the laser light component separated by the third beam splitter, and A reflection mirror that reflects the laser light component separated by the third beam splitter, and the reflection light from the optical disk Is separated into a component incident on the phase conjugate mirror and a component incident on the reflection mirror by the first beam splitter, the second beam splitter, and a third beam splitter, and from the phase conjugate mirror and the reflection mirror. 2. The optical head characterized in that the reflected light of (1) is combined by the third beam splitter, and the combined beam is incident on the signal detector. 5. The phase conjugate mirror as CdS _x Se _1-x
5. The optical head according to claim 4, wherein a colored glass filter made of a material is used. 6. The optical head according to claim 4, wherein Bi ₁₂ SiO ₂₀ is used as the phase conjugate mirror. 7. The optical head according to claim 4, wherein KNbO ₃ is used as the phase conjugate mirror. 8. An optical disk device comprising the optical head according to claim 4 and the optical disk according to claim 2.