KR970011226B1 - Optical disk apparatus - Google Patents

Abstract

No summary

Description

Optical disk unit and optical head

1A is a diagram showing a recording track on a recording layer on which an optical head according to the present invention records or reads information.

1B is a diagram showing a phase change with respect to the reference light of the light reflected from the optical disk.

1C is a diagram showing a phase of a reference light shifted in phase with respect to the reference light.

1D is a diagram showing an output waveform of a detector (optical detector).

2 is a view showing the structure of an optical head according to the present invention.

* Explanation of symbols for main parts of the drawings

1: laser light source, 2: beam splitter,

4: phase difference plate, 6: analyzer,

11 beam, 20 optical disc

Background of the Invention

The present invention relates to a technique for reading information from an optical disc, and more particularly, to read information from a phase change type optical disc that records information using a reversible phase change that occurs when light is irradiated onto the optical disc. It's about technology.

It is well known that phase-changeable optical discs have the inherent advantage of being easily rewritable without applying an external magnetic field, so it is expected that phase-changeable optical discs will make a significant difference in the field of recording / erasing optical discs in the near future. do.

In a phase change type optical disk, the recording film is partially heated by irradiating a laser light spot having a power corresponding to the information on the recording film on the disk, so that the phase is changed between the crystalline state and the amorphous state so that the information is changed. The information is reproduced by irradiating a low-power laser light on the film to determine the difference in reflectance between the crystalline state portion and the amorphous state portion of the recording film, and the intensity of light reflected from the crystalline state portion and the intensity of light reflected from the amorphous state portion. By reading with a difference of.

For example, in a phase change type optical disk using a crystal recording film having a relatively long crystallization time, recording of information on a portion of the recording film formed on the optical disk is as follows. That is, while the optical disk is rotating, the optical disk is irradiated with a laser beam to partially heat the recording film to a value higher than the melting point of the recording film portion, and thus the melted portion is rapidly cooled to record in an amorphous state.

To erase the information, it is only necessary to heat the amorphous portion of the recording film to a certain temperature within the crystallization temperature range (from the crystallization temperature to the melting point) and to maintain the temperature for a time sufficient to crystallize the recording film portion. The erasing beam used in this case has an elliptical cross section whose long axis is parallel to the direction in which the laser beam moves on the optical disk.

When trying to record new data while erasing some already recorded data, i.e., so-called pseudo overwrite, the recording film is irradiated with a recording beam having a circular cross section which directly tracks the erasing beam.

On the other hand, an optical disc using an information recording film made of a material that can be quickly crystallized uses one laser beam collimated in a circular cross section. According to the conventional method, the recording film on the optical disc is crystallized or amorphous by switching the laser light between two levels. The recording film is sufficient to raise the temperature of the recording film to a melting point, and when irradiated with a laser light having a power, the irradiated portion of the film is amorphous by cooling, whereas the crystallization of the recording film causes the power of the laser light to be higher than the crystallization temperature and to be melted. Rather, it is obtained by cooling after irradiating with a laser beam capable of raising the temperature of the film to a lower temperature.

The recording film of the phase change optical disk is a suitable film fabrication technique, for example, resistive heating vapor deposition, using a chalcogen compound such as GeSbTe, InSbTe, InSe, InTe, AsTeGe, TeOx-GeSn, TeSeSn, SbSeBi, BiSeGe, etc. ) And electron beam vapor deposition or sputtering. Since the recording film immediately after its formation is a kind of amorphous state, all of the amorphous state recording film must be subjected to crystallization processing, so that information recording which changes the state of the recording film into an amorphous state partially by laser beam irradiation is possible.

As mentioned above, in the case of a phase change type optical disc, data is recorded as an amorphous recording mark on the recording film on the crystalline recording film. Thus, the conventional method of reading data utilizes the difference in reflectivity between the crystalline state portion and the amorphous state portion. Therefore, the thickness of the recording film on the optical disk medium is selected large enough so that the difference in reflectivity can clearly distinguish between the crystalline state portion and the amorphous state portion of the recording film.

However, if the reflectance difference is large, the heat absorption of the two parts is also different. This means that the power of the laser light required to change the crystal state to the amorphous state is different from the power required to change the previous amorphous state to the new amorphous state. In this case, variation occurs in the length of the recording mark when overwriting is performed using a single beam. Such fluctuations may cause jitter in the reproduced signal, thereby degrading the quality of the reproduced signal.

In order to reduce jitter in the reproduced signal, Japanese Patent Application Publication No. 73537, published March 13, 1990, proposes to reduce the reflectance difference between the crystalline portion and the amorphous portion of the recording layer. In this case, however, it is suggested to reduce the reflectance difference. However, this causes a new problem that the level of the reproduced signal becomes too small in the prior art using the difference in reflectivity, thereby lowering the signal-to-noise ratio (S / N ratio) of the reproduced signal.

Summary of the Invention

Accordingly, it is an object of the present invention to solve the above drawbacks of a phase change optical disk device.

It is still another object of the present invention to provide a phase change type optical disc reproducing system that can improve the jitter characteristic of a signal reconstructed from a phase change type optical disc using a simple optical system.

It is also an object of the present invention to provide a novel phase change type optical disc reproducing system capable of high density recording.

An optical disk apparatus according to the present invention is a phase change type optical disk medium for recording recording data by changing a state of a portion of a recording film formed on a recording medium to a crystalline state or an amorphous state, a light source for emitting reference light, and a reference light from the light source. A beam splitter for dividing a into a first reference light and a second reference light, sending the first reference light to a phase change type optical disk medium, and passing the first reference light reflected by the medium (the light is phase shifted by data recorded on the medium). And receiving phase shifting means for phase shifting the second reference light and outputting it as a phase shifted reference light, the first reference light passed through the beam splitter reflected by the phase change type optical disk medium, and the reference shifted phase light. Detection means for outputting an electrical signal corresponding to the data is provided.

Example

Embodiments of the present invention will be described with reference to FIGS. 1A to 1D showing waveforms useful for explaining the principles of the present invention, and FIG. 2 showing the structure of an optical head using the present invention. .

First, referring to FIGS. 1A to 1D, FIG. 1A shows a recording track on a crystalline recording layer in which the optical head of the present invention records or reads information. The hatched portions in FIG. 1A represent amorphous portions in the crystalline recording layer. In the crystalline recording layer of the optical disk system using the optical head of the present invention, the reflectivity of the amorphous portion is equal to the reflectivity of the crystal portion, whereas the phase change of the light reflected from the amorphous portion is different from that of the light reflected from the crystal portion. Design to be different.

FIG. 1B shows the phase change of the reflected light, i.e., the regenerated laser light, with respect to the reference light. As much as the difference.

As will be described later, reflected light (i.e. reproduction light) and reference light are received by an analyzer in the optical head of the present invention. That is, as shown in FIG. The reference laser light out of phase is received by the analyzer together with the regenerative laser light. These laser lights interfere with each other in the analyzer and a change in the intensity of light shown in FIG. 1D occurs at the output of the analyzer. For example, the amplitude of the reproduction laser light is equal to the amplitude of the reference laser light with phase shift. When = 180 °, the output level of the analyzer is substantially lowered due to the interference of the regenerative laser light and the phase shifted reference laser light when light reflected from the crystal portion is received. In this case, the amplitude reduction of the laser light reflected from the recording mark portion, that is, the amorphous portion, is small because the phase relationship between the reflected light and the reference laser light with phase shift is out of the interference condition. Depending on the value, the amplitude may increase.

1 shows the structure of an optical head according to the invention for use in a phase change optical disk reproducing system. The main components of this embodiment are the laser light source 1, the beam splitter 2, the condenser lens 3, the phase difference plate 4, the reflector 5 and the analyzer 6.

The laser light emitted from the laser light source 1 is collimated by a collimator 7 to become a parallel beam 11. The beam splitter 2 divides the parallel beam 11 into two reference lights, and one of the two reference lights is collected by the condensing hose 3 and becomes the first reference light directed to the phase change type optical disk 2. Light reflected from the optical disk 20 passes through the condenser lens 7 and reaches the analyzer 6.

The remaining reference light (second reference light) passes through the phase retardation plate 4 and the attenuator 8 and is reflected by the reflector 5. Reflected laser light reflected by the reflector 5 passes through the attenuator 8 and the phase retardation plate 4 and passes through the beam splitter 2 to the reference laser light that is phase shifted through the second condenser lens 7. Reach the madness 6.

The laser light source 1 includes a semiconductor laser that emits a laser having a wavelength of 830 nm and an output power of 40 mw, for example. The aperture size of the condenser lens 3 is 0.55 and is mounted on a servo actuator (not shown). The phase delay plate 4 is a variable phase delay type having a structure similar to a well-known cabinet compensator or soleil comensator. An attenuator 8 disposed between the phase retardation plate 4 and the reflector 5 is provided for adjusting the level of the reference laser light which is phase shifted in the analyzer according to the level of the reflected light.

Next, an optical disk having a small retardation difference and a large retardation difference is prepared for a laser beam having a wavelength of 830 nm. That is, on the polycarbonate ester substrate having a pregroove having a diameter of 130 nm and a thickness of 1.2 nm, a second protective film made of a mixture of Zns and Sio ₂ , an Al reflective thin film, was prepared in the order listed above by the Markttron sputtering technique. Form continuously. The thickness of the first protective thin film is 150 nm, the thickness of the recording thin film is 10 nm, the thickness of the second protective thin film is 60 nm, and the thickness of the reflective thin film is 50 nm. The reflectance difference of this optical disk is 2% when the wavelength is 830 nm, and the phase difference is 170 degrees. The overwriting to the optical disk is performed using the optical head of FIG. 2, and the characteristics of the reproduction signal are examined.

That is, a 8.4 MHz signal (50% duty) is initialized and formed on an optical disc, recorded on a circular track with a radius of 30 nm, and recorded by irradiating a recording laser light with a power of 13mw while rotating the optical disc at 360 rpm and then recording 7mw. The 2.2 MHz signal (50% duty) is overwritten on the same track by irradiating a power-supply erasing laser beam.

Then adjust the phase retardation plate 4 so that the phase difference between the regenerative laser beam and the reference laser beam is 180 ° in the portion where no tracked signal is recorded, and the power levels of the two laser beams are the same using the attenuator 8. Make it. Under these conditions, the reproduced signal has no phase jitter caused by overwriting.

As described above, according to the present invention, phase information recorded on an optical disc can be efficiently reproduced by a simple optical system. According to the present invention, even if a small phase change can be detected by selecting an interference condition, that is, by selecting a phase condition of a reference laser light, the disk can be designed more freely. Also, the reproduction system of the present invention is particularly suitable for a mark edge recording system for recording information on the edge portion of a recording mark and enables high density recording.

Claims (6)

An optical disk apparatus comprising: a phase change type optical disk medium including the recording film for recording recording data by changing a portion of the recording film into either a crystalline state or an amorphous state by emitting a reference light; A light source and a reference light emitted from the light source into a first reference light and a second reference light, supplying the first reference light to the phase change type optical disk medium, and reflecting the first reference light reflected by the phase change type optical disk medium. Beam splitter for transmitting a light beam to a detector (photodetector), wherein the first reference light reflected by the phase change optical disk is phase-shifted by the recorded data. Phase shifting means for outputting to the analyzer as the reference light, and the first reference light and the phase reflected by the phase change type optical disk medium and passing through the beam splitter And an analyzer for receiving the shifted reference light and outputting an electrical signal corresponding to the recorded data. 2. The recording film of the phase change type optical disc medium according to claim 1, wherein the recording film has a reflectivity of the recording film in an amorphous state, and the reflectivity of the recording film in an amorphous state is substantially the same as that of an image of reflected light from the recording film in a crystal state. And the thickness is selected so that the reflected light from the recording film is different. 2. The method of claim 1, wherein the phase shifting means phase shifts the second reference light to output the second reference light that is phase shifted as the third reference light, and phase shifts the fourth reference light to phase shift the fourth reference light. And a reflection plate for reflecting a third reference light to direct the fourth base light phase shifted to the phase retardation plate. The optical disc apparatus according to claim 3, wherein the phase difference between the second reference light and the phase shifted reference light is 180 degrees. 5. An optical disk apparatus according to claim 4, further comprising an attenuator provided between said phase retardation plate and said deflection plate. An optical head for recording and reading recording data on a recording film of a phase change type optical disc medium for recording recording data by changing the phase of the recording film into one of a crystalline state and an amorphous state corresponding to the recording data. The optical head having substantially the same reflectance as that of the recording film in the crystalline state with respect to the reference light, and reflecting light from the recording film in the amorphous state different from the reflected light from the recording film in the crystalline state; A light source for emitting a reference light, and a reference light emitted from the light source is divided into a first reference light and a second reference light, and the first reference light is supplied to the phase change type optical disk medium, the phase change type optical disk medium Beam splitter for transmitting the first reference light reflected by the beam to a detector (photodetector)-the phase change type The first reference light reflected by the optical disk is phase-shifted by the recorded data-, phase shift means for shifting the phase with the second reference and outputting it to the analyzer as the phase shifted reference light, and the phase change. And an analyzer for reflecting by a fluorescent disk medium and receiving a first reference light and a phase shifted reference light passing through the beam splitter, and outputting an electrical signal corresponding to the recorded data.