JPH0512673A - High density recording and reproducing system for optical disk device - Google Patents

Abstract

PURPOSE:To decrease a light spot diameter substancially without degrading a regenerating signal S/N by forming a temperature dependency optical shutter layer absorbing a reproducing laser wavelength at normal temperature and transmitting it at high temperature on a recording medium. CONSTITUTION:A temperature dependency transmissivity variable medium 14 whose light transmissivity is raised at high temperature is formed to the objective lens side of an optical recording and reproducing layer 15. At the time of reproducing, when outgoing laser power is controlled and the medium temperature in the light spot 4 and in the vicinity of the spot is controlled, the temperature of the medium 14 in the vicinity of the light spot 4 is raised high at the rear side of the advancing direction of the light spot 4 when the optical disk is rotated. Thus, only the area 11 where the high temperature area 10 of the medium temperature and the light spot 4 are superposed us participated to reproducing and a substancial reproducing spot diameter is reduced than the light spot diameter 4. Further, since signal reflection from the recording and reproducing layer 15 is generated only at the area of the high medium temperature no S/N is degraded trough the substancial light spot is reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high density recording / reproducing system for an optical disk device.

[0002]

2. Description of the Related Art FIG. 16 is a principle diagram showing a method of recording a minute signal smaller than the light spot diameter in conventional magneto-optical recording. In the figure, 1 is a laser beam, 2 is an objective lens, 3 is an optical disc, 4 is a light spot condensed by the objective lens 2, 5 is a temperature distribution on the disc medium, and 6 is a Curie when, for example, magneto-optical recording is performed. A recordable temperature corresponding to the temperature, and 7 is a minute signal to be recorded.

FIG. 17 is a principle diagram showing a method of reproducing a light spot having a diameter of half or less of a reproducing light spot diameter in conventional magneto-optical reproduction. In the figure, 8 is a disc moving direction, 9 is a recording mark, 10 is a high temperature region on the disc medium, 11 is a detection region on the disc medium, 12 is a reproducing layer on the disc medium, and 13 is a recording layer on the disc medium.

FIG. 18 shows the recording wavelength dependence of a reproduced signal in the conventional system, where the vertical axis represents the reproduced signal S / N,
The horizontal axis indicates the recording (track) direction density of the recording signal and the recording wavelength.

In order to increase the density of the magneto-optical disk, it is necessary to establish both recording technology and reproducing technology.
Regarding recording, in the light spot formed by the laser on the disk 3 in FIG. 16, the temperature in the vicinity of the center is highest and the temperature distribution 5 is obtained. Therefore, the temperature near the center easily reaches the recordable temperature. Therefore, if the Curie temperature of the recording material is set to a temperature corresponding to the center of the light spot 4, the recording is smaller than the light spot diameter such as the minute signal 7. It becomes possible to form spots. Therefore, in recording, high density recording is possible by shortening the laser irradiation interval while partially overlapping the light spots.

On the other hand, in reproduction, assuming that the laser wavelength is λ and the numerical aperture of the objective lens 4 of the optical pickup is NA (a coefficient determined by the lens diameter and the focal length), the reproduction limit wavelength is determined by λ / 2NA. For example, in the current optical disk device, λ = 780 nm, NA
= 0.5, the detection limit is about 0.74 μm. In this way, when the wavelength of the laser to be used is determined, the practical objective lens NA is almost determined, so that the physical or optical limit is determined. Therefore, in order to realize a high-density magneto-optical disk, it is necessary to shorten the wavelength of the laser and increase the numerical aperture of the objective lens, and to put the red semiconductor laser into practical use and SHG (double harmonic generation element). The development of green and blue lasers by is progressing.

In addition to the method using the short wavelength laser as described above, attention is paid to the phenomenon that only the high temperature portion can be read out due to the temperature difference in the light spot generated during laser irradiation, and by utilizing this phenomenon, As a result, there is a method of obtaining the same effect as that of substantially reducing the light spot area.

In this method, the material of the recording layer 13 in FIG. 17 has a large coercive force, and the reproducing layer 12 in FIG.
To have a small holding power. At this time, by applying an initializing magnetic field before reproduction, the magnetization directions of the reproduction layer 12 near the detection signal are all reversed in one direction to erase. Next, by irradiating a reproducing laser on the reproducing layer 12 which has been erased in one direction as described above, the reproducing layer 1
Only the high temperature portion 2 is heated to the Curie point or higher, the recorded magnetic information is transferred from the recording layer 13, and a minute signal is detected.

As described above, an effect equivalent to the fact that the light spot area is substantially reduced can be obtained, so that the apparent light spot diameter becomes small, and even in the existing semiconductor laser, the conventional detection limit recording wavelength is obtained. , For example 0.74
It is possible to reproduce a recording wavelength shorter than half the μm, and the resolution can be more than doubled.

However, since the actual area of the light spot on the board is not reduced, it is caused by the magnetization of the medium contained in the reproduced signal and the nonuniformity of the reflectance.
The amount of medium noise is the same as that of the conventional magneto-optical reproducing method using the original large light spot as it is, whereas the reproducing signal level is the reproducing layer (12) transferred from the recording layer 13. The area at is smaller than the light spot area on the surface of the board.

Therefore, the higher the recording density, the more
Since the ratio of the area that contributes to the signal reproduction to the area of the light spot on the board becomes small, it is natural that the C / N of the reproduced signal becomes smaller.

[0012]

Since the high-density recording / reproducing method in the conventional optical disk device is performed based on the principle as described above, the higher the density of recording, the signal reproduction with respect to the light spot area on the surface of the board. There is a problem in that the ratio of the areas contributing to the above becomes smaller and the C / N of the reproduced signal becomes smaller. Also, because it uses magnetic transfer,
Only applicable to magneto-optical recording / reproducing system, phase change recording / reproducing system, write-once system which is a drilling system, current C
There is also a problem that the above-mentioned system cannot be applied to the reproduction-only system, which is the same as the D player and the like, and the high density cannot be achieved.

Further, in the above-mentioned method, since the apparent spot diameter is determined by the difference in temperature rise in the light spot portion, the temperature control on the medium is strict and the temperature detection at the light spot on the medium cannot be performed in the optical disk. There is also a problem that it is extremely difficult to control the laser power.

Further, if an attempt is made to increase the recording density in the track pitch direction to increase the recording density, the track pitch becomes extremely small with respect to the light spot diameter, and in the tracking signal reproducing method such as the push-pull method, an accurate tracking signal is obtained. There was also a problem that tracking could not be performed well due to problems such as being unable to catch.

The present invention has been made in order to solve the above-mentioned problems, and it is possible to increase the density without deterioration of the signal S / N, control the apparent light spot diameter, and reproduce only. An object of the present invention is to obtain an optical density recording / reproducing system for an optical disc device capable of realizing high density recording / reproducing compatible with a phase change system.

[0016]

In the first invention,
A temperature-dependent variable light transmittance medium layer is provided on the information recording layer (on the side where the laser is emitted from the objective lens), and the temperature of the rear part of the light spot on the board in the light spot traveling direction is high. To increase the laser light transmittance in the high temperature portion of the temperature-dependent light transmittance variable medium layer, and reduce the laser light transmittance of the temperature-dependent light transmittance variable medium layer in other portions. As a result, the apparent light spot diameter is reduced.

In the second aspect of the invention, the fact that the temperature is high in the rear portion of the light spot on the board surface in the light spot advancing direction is used to transmit the laser light in the high temperature portion of the temperature dependent light transmittance variable medium layer. The ratio is made low, and the other portions are made to reduce the apparent light spot diameter by increasing the laser light transmittance of the temperature-dependent light transmittance variable medium layer.

In the third invention, at the time of recording / reproducing, the reflectance of the portion having a low light transmittance of the temperature-dependent light transmittance variable medium is the light transmittance of the temperature-dependent light transmittance variable medium. Since the reflectance is sufficiently low compared to the reflectance in the high part, the output laser is so that the amount of light received by the photodetector that monitors the reflected light from the disk in the optical head during recording and reproduction is always constant. By controlling the power, it is possible to control so that the area ratio of the portion having the high light transmittance in the entire area of the light spot is always constant.

In the fourth invention, the amplitude of the reproduction signal or the tracking error signal when the light spot crosses the guide groove of the disk is set by the groove in the area of the region having high light transmittance in the third invention. The output laser power is controlled so that the amplitude of the modulated signal becomes maximum, and the area of the region of high optical transmittance that contributes to the signal reproduction on the disc is optimized.

In the fifth aspect of the present invention, the heat capacity of the temperature-dependent light transmittance variable medium is made larger than that of the recording / reproducing layer, so that the recording medium passes through a region having high light transmittance having the small spot area at the time of recording. The recording is performed on the recording medium and the irradiation of the recording laser power is stopped before the spot area becomes large, thereby enabling high density recording having a small spot.

[0021]

In the signal reproduction according to the first and second aspects of the present invention, the temperature-dependent light transmittance variable medium partially increases in temperature in the light spot to increase or decrease the light transmittance. In order to transmit the laser light to the recording / reproducing layer, only the apparent reflected light is returned to the optical head, which has a change in the amount of reflected light in punching recording or phase change recording and a change in the Kerr rotation angle in magneto-optical recording. The signal can be reproduced with a small light spot. Further, since light is not sufficiently reflected in portions other than those that contribute to signal reproduction, even if the spot diameter apparently becomes small, noise due to the medium also decreases, and S / N does not deteriorate so much. Further, according to the third and fourth inventions, the apparent spot diameter that contributes to the reproduction signal can be automatically optimized by controlling the laser power, so that it is possible to cope with changes in the device temperature and room temperature and variations in the medium. It is possible to Further, according to the fifth aspect, the edge of the recording pit can be accurately written even during recording.

[0022]

【Example】

Example 1. FIG. 1 is a sectional view of an optical disk used in an optical disk device according to an embodiment of the present invention. In the figure, reference numeral 14 is made of a material such as a polymer material, absorbs light of a specific laser wavelength at room temperature, and does not absorb light of the specific laser wavelength as the medium temperature rises, and at the same time, specifies the specific laser wavelength. It is a temperature-dependent transmittance changing medium in which the light transmittance of the laser wavelength is increased and the medium temperature is lowered again, and the light of the specific laser wavelength is absorbed. Reference numeral 15 denotes an information recording / reproducing layer formed on the substrate of the optical disk for recording / reproducing information by using uneven pits or reflectance change due to a phase change of the recording material, or for performing magneto-optical recording / reproducing. is there.

FIG. 3 shows a change in medium during reproduction of an optical disc used in the optical disc apparatus according to the embodiment of the present invention. FIG. 4 shows a timing chart of medium change in FIG.

FIG. 5 is a block diagram of an optical disk device according to an embodiment of the present invention. In the figure, 16 is a disk motor for rotating the optical disk 3, 17 is an optical head, 18 is an output signal of a photodetector mounted on the optical head,
Reference numeral 19 is a minute signal amplifier circuit for amplifying the output signal 18 of the photodetector, and 20 is an automatic laser power control circuit for controlling the laser drive signal 17 ″ based on the laser monitor detection signal 17 ′.

Further, 21 is a recording / reproducing spot diameter adjusting circuit for giving a reference of the automatic laser power control circuit 20 for controlling the recording / reproducing spot diameter based on the output of the minute signal amplifying circuit 19, and 22 is a minute signal amplifying circuit. The waveform equalization / demodulation circuit for waveform-equalizing and demodulating the recording / reproducing information which is the output of 23, 23 is a tracking control circuit for tracing the light spot from the objective lens 4 in the guide groove of the disc, and 24 is the objective lens. A focus control circuit for making the light spot from 4 follow the surface deviation of the disc, 25 a system control circuit for comprehensively controlling the system such as tracking control, focus control, disc rotation control, laser power control, and 2
A reproduction signal, which is the output of the 6-waveform equalization / demodulation circuit, and 27 is an actuator drive signal for moving the objective lens 4.

FIG. 6 shows parts 20, 21, 17, and 19 which form a recording / reproducing spot diameter adjusting system according to an embodiment of the present invention.
3 is a more detailed block diagram of FIG. In the figure, 30,
Reference numeral 31 is an IV conversion circuit for converting the outputs of the photodetectors 28 and 29 into IV information and converting it into voltage information. Reference numeral 32 is an integration of the output of the IV conversion circuit 30 to obtain average reflected light from the disc. And 33 is an integrator for calculating the average laser emission power based on the output of the detector 29 that monitors the light emission power from the laser 40.

Reference numeral 34 is a phase compensation circuit for maintaining stability and quick response in a laser power control loop for controlling the average laser emission power based on the output of the detector 29 for monitoring the light emission power from the laser 40. Three
5 is an apparent light spot diameter command value 36 and an integrator 32.
The subtractor for calculating the spot diameter error by subtracting the calculated value of the average reflected light from the disc, which is the output of
Reference numeral 7 is a subtracter for providing a reference to the laser power control loop and producing a laser power error signal. 38
Is an amplifier for amplifying the output of the subtractor 37 which produces a laser power error signal. Reference numeral 39 is a driver for driving the laser 40, and 41 and 42 are polarization prisms (beam splitters) arranged in the optical head 17.

FIG. 7 is a block diagram for controlling the apparent spot diameter so that the reproduction signal amplitude becomes maximum.
In the figure, 44 is a signal amplitude detection circuit composed of an envelope detector, 45 is an A / D converter for analog-digital conversion of the output of the 45 signal amplitude detection circuit, and 47 is an optimum spot based on the output of the microcomputer. It is a digital-analog converter (D-A converter) for adjusting the diameter.

FIG. 8 is a block diagram for controlling the apparent spot diameter so that the tracking error signal amplitude is maximized. In the figure, 48 is a track error signal generation circuit for generating a track error signal based on the reflected light from the disc, 49 is a D-A converter that gives a control voltage for moving the actuator, 50 is a changeover switch, and 51 is a disc guide. A tracking control circuit for tracing a light spot on the groove.

FIG. 9 is a diagram showing the open loop characteristics of the control system in the block diagram of FIG. 7 or 8. FIG. 10 shows how the medium changes when the spot diameter control shown in FIGS. 7 and 8 is performed during reproduction. FIG. 12 is a diagram showing a timing chart in FIG.

FIG. 12 shows how the medium changes when the spot diameter control shown in FIGS. 7 and 8 is performed during recording. FIG. 13 is a diagram showing a timing chart in FIG. FIG. 14 is a diagram showing the temperature distribution of the recording / reproducing layer of FIG.

FIG. 15 is a software flowchart of the spot diameter control system in the microcomputer of FIGS. 7 and 8.

As shown in the sectional view of FIG. 1, the optical disk used in the optical disk apparatus of the present invention has a temperature-dependent variable light transmittance medium formed on the optical recording / reproducing layer (on the objective lens side). is there. The temperature-dependent variable light transmittance medium is formed of, for example, a polymer material or an organic material, and has a material having a high light transmittance in a high temperature region with respect to the medium temperature as shown in FIG. is there. The above-mentioned change in transmittance may be due to an increase in light transmittance due to melting of the material or a change in the regularity of the molecular arrangement such as a liquid crystal material. Further, the light transmittance may be changed by crystallization of, for example, chalcogenide adhered in an amorphous state by heating and cooling, such as a phase change material. However, the temperature-dependent light transmittance variable medium can maintain a stable state and a metastable state at room temperature, as developed in general optical recording media, and can reversibly shift to each state. It is not necessary to have such a structure, and any material may be used as long as the state of the material changes with each medium temperature and the light transmittance changes accordingly.

When the temperature-dependent light transmittance variable medium as described above is formed on the recording / reproducing layer and the emitted laser power is controlled to control the medium temperature in the light spot and in the vicinity thereof even during reproduction, As shown in 3, it is possible to reduce the apparent light spot diameter. Generally, as for the medium temperature near the light spot, when the optical disc is rotating, it is natural that the rear side in the traveling direction of the light spot becomes high temperature and the front side becomes low temperature as described in the conventional example. . This is because the rear part of the light spot has a longer light energy storage time.

Therefore, as shown in FIG. 3, the light transmittance of the temperature-dependent light transmittance variable medium becomes high in a region where the medium temperature is high, and only in the region where the transmittance is high, the reflected light of the recording / reproducing layer is reflected by the objective lens. Can be returned to.

Generally, the recorded reproduction signal cannot be reproduced with a pit diameter of half or less of the reproduction light spot. However, in this case, as shown in FIG. 3, only the area where the medium temperature is high and the area where the light spot 4 overlaps are involved in the reproduction, so that the substantial reproduction spot diameter is sufficiently larger than that of the light spot 4. Can be made smaller. As a result, as shown in FIGS. 3 and 4, for example, it is possible to reproduce even a recording pit having a light spot diameter of half or less.

Similarly, in the method of transferring magnetism shown in the conventional example, the substantial light spot diameter can be made small, but all the reflected light of the light spot on the medium involved in the reproduction signal is utilized. On the other hand, in this method, light is absorbed in the region where the medium temperature that is not involved in reproduction is not so high (low light transmittance).
Does not contribute much to the playback signal.

However, conventionally, the smaller the substantial light spot diameter is, the smaller the proportion of the reflected light amount relating to the reproduction signal in the light reflected from the medium becomes, and the output of the reproduction signal decreases. . At this time, of course, since there is reflection from the medium in all regions of the light spot, the medium noise due to the surface properties of the medium and minute variations in the material remains constant. Therefore, it goes without saying that the S / N (noise with respect to the signal output) of the reproduced signal deteriorates as the substantial light spot diameter decreases.

In this system, since the signal is reflected from the recording / reproducing layer only in the region where the medium temperature is high, the reproduced signal output is lowered even if the actual light spot diameter is reduced. At the same time, since the reflection of light from a portion unrelated to the signal reproduction is reduced, the noise level due to the medium is also reduced, and the S / N of the reproduction signal is not deteriorated so much and the substantial light spot diameter is reduced. can do.

Further, in the conventional magnetic transfer system, the tracking operation at the time of reproduction is performed by the light spot 4. Therefore, if the disc guide groove pitch is narrowed in order to forcibly increase the density in the track pitch direction, the light spot 4 becomes larger than the guide groove pitch in the push-pull tracking error generating method, for example. Error detection due to optical interference cannot be performed,
Tracking control cannot be performed normally. However, in this method, the reflection of light is mainly performed only in the high temperature region of the medium temperature in the light spot 4,
Since the light spot involved in tracking is also a substantially small light spot (a region where the light spot 4 and the medium high temperature region overlap), the tracking operation can be normally performed even if the track pitch is narrowed. In addition, since magnetic transfer was used in the past, it could only be used in a magneto-optical recording / reproducing system, but in this system, the light spot diameter itself involved in signal reproduction is optically small, so phase change recording or Of course, it can also be used for read-only optical discs such as write-once and CD.

Here, the relationship between the characteristic change of the medium during reproduction and the reproduction laser power in the embodiment of the present invention is expressed as shown in FIG. When the disc was rotated and the light spot was scanned at a certain linear velocity, the reproduction laser power was gradually increased, and as shown in the figure, the laser power was relatively weak in the rear part of the light spot. In contrast, the medium transmittance of the temperature-dependent variable light transmittance medium is high, whereas the medium transmittance does not increase in the front portion unless the laser power is relatively high. for that reason,
For example, when reproducing an optical disc having recording pits that are less than half of the reproduction light spot 4, the temperature-dependent light transmittance variable medium in the rear part of the light spot in FIG. 4 has a high light transmittance and the front part has a low light transmittance. When the reproduction laser power is set to, the actual reproduction spot diameter and the recording pit diameter match at a predetermined laser power in the figure, and the reproduction signal output can be taken out as shown in FIG.

In the present invention, as described above, even if the temperature-dependent light transmittance variable medium is configured to have a high light transmittance at a high temperature and a low light transmittance at a low temperature, conversely, the temperature-dependent light transmittance variable medium is variable. The same effect can be obtained by configuring the medium composition so that the light transmittance becomes low at a high temperature and becomes high at a low temperature. However, at this time, it goes without saying that the substantial light spot shape becomes a region outside the in-light spot detection region 11 shown in FIG. Therefore, the substantial spot shape at this time is a crescent shape.

As can be seen from FIG. 4, in this system, if the reproducing laser power can be accurately set, the light spot diameter can be accurately determined. This also applies to the conventional magnetic transfer method. However, in the conventional case, since there is no means for measuring the temperature distribution on the medium,
The laser power could not be controlled. For this reason, there has been a problem that the medium temperature changes during reproduction due to the medium temperature change due to environmental changes in the apparatus and room temperature, and the actual light spot diameter changes. The above-mentioned substantial change of the light spot diameter not only deteriorates the signal output in high-density signal reproduction, but also causes the signal reproduction to become impossible in some cases.

However, in the embodiment of the present invention, since the light transmittance of the optical disk medium changes, the area of high light transmittance in the temperature dependent light transmittance variable medium in the portion where the light spot hits is: Depending on the proportion of the total area of the light spot 4,
The total light reflectance of changes. For example, in the case where the temperature-dependent variable light transmittance medium has a high light transmittance at a high temperature and a low light temperature at a low temperature, the lower part of the high light transmittance relating to signal reproduction is Although the light is reflected by the recording / reproducing layer, the light is absorbed in the non-participating portion. Therefore, if the total light reflectance of the light spot 4 is measured, the temperature-dependent light of the portion hit by the light spot is measured. It is possible to detect the ratio of the area of high transmittance in the variable transmittance medium to the total area of the light spot 4.

Therefore, when the optical disk device is constructed with the structure as shown in FIG. 5, the output of the photodetector for detecting the light reflected from the disk is amplified by the minute signal amplifying circuit 19 and then the recording / reproducing spot diameter adjusting circuit. By controlling the reference of the automatic laser power control circuit by 21, it becomes possible to control the laser power so that the light reflected from the disk is always constant. In this way, if the disc reflected light amount at the time of reproduction is controlled to be always constant, that is, the region of high light transmittance in the temperature-dependent light transmittance variable medium of the portion on which the light spot of the present invention hits, It is possible to always keep the ratio of the light spot 4 to the entire area constant, and to control the actual reproduction spot diameter (for example, the region of the light spot 4 having a high light transmittance of the temperature-dependent light transmittance variable medium). Is possible.

Such a recording / reproducing spot diameter adjusting system is specifically constructed as shown in FIG. 6, for example. Laser 4
A part of the light emitted from 0 is split by the polarization prism 41 to the photodetector 29. This dispersed light is I-
The V conversion circuit 31 detects what kind of laser power is currently being emitted. Since the actual light may be optically modulated during recording, for example, it is input to the integrator 32 to extract the average laser emission power.

Next, in order to maintain the quick response and stability of the automatic laser power control loop, this error is input after being input to the phase compensation circuit 34, compared with the laser power set value, and the deviation from the set value is calculated. It is amplified and supplied as a drive current to the laser 40 by the laser driver 39.
In this way, the laser power control loop is formed, and the laser is controlled to always emit light according to the laser power setting value.

Here, the reflected light information of the optical disk, which is the output of the photodetector 28, is converted into a voltage value by the IV conversion circuit, and is taken out by the integrator 32 as the average value of the disk reflected light quantity. Of the total light reflectance of the above-mentioned temperature-dependent light transmittance variable medium in the portion where the light spot hits, occupies a ratio to the entire area of the light spot 4. Since it is shown, that is, it is a value corresponding to the above-mentioned apparent light spot diameter.

Therefore, the apparent light spot diameter command value 36 in FIG. 6 is compared with the output of the integrator 32,
After calculating how much the spot diameter deviates from the command value by the subtractor 35, and then giving this as the control command value (reference) of the laser power control loop, the apparent size of the light spot diameter can be obtained. The laser power can be controlled so that is always in accordance with the command value. The control band of this light spot diameter adjustment loop is
As shown in the open loop characteristic of FIG. 9, the control band is set sufficiently lower than the control band of the automatic laser power control loop, and the integrator 32 of FIG. It secures open loop gain in the range, and at the same time secures stability.
In this way, the laser power can be adjusted stably. That is, it is possible to keep the apparent light spot diameter always constant even if there are variations in the temperature and room temperature in the apparatus, and variations in the material and composition of the temperature-dependent light transmittance variable medium.

Next, how to set the optimum value of the apparent spot diameter command value will be described. FIG. 7 shows an example of a method of varying the apparent light spot diameter command value so that the amplitude of the reproduction signal is maximized. The output of the photodetector 30 that detects the light reflected from the disc is I- After passing through the V converter 30, the waveform equivalent circuit 2
2, the signal is processed as a reproduction signal, and the reproduction signal after the waveform equalization is envelope-detected by the signal amplitude detection circuit 44, and this signal amplitude information is analog-digital converted by the A / D converter. It is input to the microcomputer 46.

At this time, first of all, as the system of the entire apparatus,
After the optical disc rotates and gives an appropriate spot diameter command value to the laser power control circuit, the focus servo is operated on the objective lens to follow the disc surface deviation and the optical spot is tracked to the disc guide groove. So, the tracking servo must also be applied. In this state, the optimum spot diameter command value, which is the output of the DA converter 47, is shifted to a slightly larger value, for example, by an algorithm of the microcomputer based on the output of the AD converter 45 in FIG. At this time, if the reproduced signal amplitude becomes a little smaller, the optimum spot diameter command value is shifted to a slightly smaller one. In this way, the optimum spot diameter command value that maximizes the reproduction signal amplitude is searched for, and the change in the optimum spot diameter command value is stopped when the reproduction signal amplitude becomes maximum.

The above-described optimum value search method is well known as a hill climbing method, and is a general method often used in VTR tracking control and the like. For example, when reproducing a disc recorded with half the recording pits with respect to the light spot 4, if the apparent light spot diameter is gradually decreased from the diameter of the light spot 4, the apparent light spot diameter is reduced. When the diameter of the light spot becomes almost the same as the diameter of the recording pit, the signal amplitude becomes maximum, and when it becomes further smaller, the amount of light reflected from the disk decreases and the reproduction signal amplitude decreases. Therefore, it is possible to search for an apparent optimum spot diameter by using the hill climbing method.

The reproduced signal used at this time is the equivalent circuit 22.
The signal amplitude may be a signal after IV conversion before passing through, and if the recording / reproducing signal is an analog FM-modulated signal, a signal obtained by extracting the carrier component of the FM signal with a bandpass filter is used. It may be input to the detection circuit 44.

The means for optimizing the apparent light spot diameter by using the reproduced signal has been described above. However, even when the recording pit is not formed such as during recording, the apparent light spot as described above is used. In some cases, means for optimizing the diameter may be needed. In this case, as shown in FIG. 8, there is a method of optimizing the apparent light spot diameter so that the tracking guide groove crossing signal amplitude is maximized.

In FIG. 8, the track error signal generating circuit 48 generates a track error based on the output of the photodetector 28 which detects the reflected light from the disk. At this time, it goes without saying that the tracking error can be similarly detected regardless of whether the tracking method is the push-pull method or the three-beam method.

The track error signal obtained as described above is as shown in FIG. 11 when the objective lens in the optical head in the optical disk device operates only the focus servo and the tracking servo does not operate. The track error signal is modulated due to the crossing signal of the track guide groove due to the eccentricity. In the configuration of FIG. 8, when the objective lens 2 is moved in the track crossing direction by the actuator by the DA converter 49 based on the command of the microcomputer 46, the track error signal is modulated by the guide groove regardless of the presence or absence of the disc core. Needless to say, occurs.

Therefore, as described above, the objective lens 2 is moved in the track crossing direction by the actuator by the DA converter 49 based on the command of the microcomputer 46, and the track error signal is guided regardless of the presence or absence of the core of the disc. The groove crossing is caused to occur, and the signal amplitude detection circuit 44 detects the amplitude of the modulation signal of the track error signal due to the crossing of the guide groove.

Next, the amplitude of the track error signal modulated by the A / D converter 45 is calculated by the algorithm in the microcomputer 46 as shown in FIG. The amplitude of the track error signal modulated as shown in FIG. 11 is maximized while changing the command value. When the amplitude of the modulated track error signal becomes the maximum, if the operation is performed so as to stop the change of the optimum light spot diameter command value, even in the area where the reproduction signal is not recorded at the time of recording, etc. The optimum spot diameter can be set.

Further, in the push-pull tracking signal detection method in which the optimum spot diameter is obtained by using the track error signal as described above, not only the density in the line direction but also the density in the track pitch direction can be increased. It can be seen that even when it is performed, the apparent light spot is automatically adjusted to have an optimum light spot diameter for the track pitch of the disk as shown in FIG.

As described above, in the optical disk device according to the embodiment of the present invention, the transmittance change region of the temperature-dependent light transmittance variable medium is overlapped with the light spot 4 by optimally controlling the laser power. It is possible to accurately control the size of the area (apparent light spot).

In the optical disk according to the present invention, since the change in the transmittance of the temperature-dependent light transmittance variable medium is caused by the temperature change of the medium, the time required for the temperature rise due to the heat capacity of the medium and the transmittance variable temperature are High-density optical recording becomes possible by setting and setting the temperature required for recording in the optical recording / reproducing layer.

FIG. 12 is a diagram showing the principle of high-density recording in the case of magneto-optical recording in the embodiment of the present invention. In the optical disc of the present invention, when the medium condition is set such that the heat capacity of the temperature-dependent light transmittance variable medium (optical shutter layer in FIG. 12) is larger than that of the recording medium, pulse-shaped as shown in FIG. When irradiated with the recording laser, the high temperature region (high light transmittance region) = (apparent light spot) of the optical shutter layer is sufficiently smaller than the light spot 4.

As compared with the temperature increase of the optical shutter layer having a large heat capacity as shown in FIG. 13, the temperature increase of the recording / reproducing layer having a small heat capacity therebelow is steeper, so that the temperature of the recording / reproducing layer below is immediately cured. The temperature is reached and recording is possible. On the other hand, the optical shutter layer gradually expands the high temperature region, and the apparent light spot gradually increases. However, if the irradiation of the recording laser power is stopped before the apparent high temperature area in the optical shutter layer becomes large, a small recording pit is formed by the laser light that passes through the small area with high light transmittance in the optical shutter layer. be able to.

At this time, in the above-mentioned method, since the light reflection from the disk at the time of recording can be monitored and the apparent light spot diameter control of FIG. It is also possible to adjust. Also,
As can be seen from the temperature distribution of FIG. 13, the conventional temperature distribution due to the light spot is a Gaussian distribution, whereas in the present embodiment, the laser light is transmitted only in the portion where the light transmittance of the optical shutter layer is high. Therefore, only the recording pit portion can have a high temperature distribution. In this case, it goes without saying that if a heat insulating layer is inserted between the optical shutter layer and the recording / reproducing layer, the temperature can be raised only in the recording pit portion.

Conventionally, changes in room temperature and in-apparatus temperature,
Due to variations in the composition of the medium, there are problems that the recording pit diameter changes and the edges of the recording pit become unstable. However, as described above, in the present embodiment, since recording can be performed by utilizing the change in the light transmittance of the optical shutter layer,
The edges of the recording pits are recorded more accurately than in the conventional method in which the Curie temperature of the medium is increased and recording is performed by using the tip portion of the Gaussian temperature distribution.

[0066]

As described above, according to the present invention, signals are not reflected from the recording / reproducing layer only in a region where the medium temperature is high. Therefore, even if the substantial light spot diameter is reduced. At the same time as the reproduction signal output decreases, the reflection of light from the portion unrelated to the signal reproduction also decreases, so the noise level due to the medium also decreases, and the S
It is possible to reduce the substantial light spot diameter without significantly degrading / N.

Further, in the past, since magnetic transfer was used, it could be used only in the magneto-optical recording / reproducing system. However, in this system, the light spot diameter itself involved in signal reproduction is optically small, so It can also be used for change recording and read-only optical disks such as write-once and CD.

Since the laser power can be controlled so that the apparent light spot diameter is always in accordance with the command value, variations in temperature and room temperature in the apparatus, temperature-dependent variable light transmittance medium material It is possible to always keep the apparent light spot diameter constant, even if there are variations in composition.

Not only when the density is increased in the line direction, but also when the density is increased in the track pitch direction,
Since the apparent light spot can be automatically adjusted to have the optimum light spot diameter for the track pitch of the disc, the tracking control operation can be performed normally even if the track pitch is increased. .

Further, since it is possible to monitor the light reflection from the disc during recording and simultaneously control the apparent light spot diameter shown in FIG. 6, it is possible to adjust the recording pit diameter during recording. .

Whereas the conventional temperature distribution due to the light spot is a Gaussian distribution, in the present invention, since the laser light passes only through the portion of the optical shutter layer where the light transmittance is high, only the recording pit portion is present. It is possible to have a high temperature distribution. Therefore, conventionally, there have been problems that the recording pit diameter changes and the edges of the recording pit become unstable due to changes in room temperature and in-apparatus temperature, variations in the composition of the medium, etc. Since recording can be performed by using the change in light transmittance of the shutter layer, recording pits can be used as compared with the conventional method in which the Curie temperature of the medium is increased and recording is performed by using the leading end of the Gaussian temperature distribution. There is an effect such that the edge of is accurately recorded.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of an optical disc used in an optical disc device according to an embodiment of the present invention.

FIG. 2 is a diagram showing the relationship between the medium transmittance and the medium temperature of FIG.

FIG. 3 is an explanatory diagram showing a medium change during reproduction of an optical disc used in the optical disc device according to the embodiment of the invention.

FIG. 4 is a timing chart showing medium changes in FIG.

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

FIG. 6 is a configuration diagram of a light spot diameter adjustment system in an embodiment of the present invention.

FIG. 7 is a block diagram for controlling the apparent spot diameter so that the reproduction signal amplitude is maximized.

FIG. 8 is a block diagram for controlling the apparent spot diameter so that the tracking error signal amplitude is maximized.

9 is a diagram showing open loop characteristics of the control system in the block diagram of FIG. 7 or FIG.

FIG. 10 is a diagram showing how the medium changes when the spot diameter control shown in FIGS. 7 and 8 is performed during reproduction.

11 is a diagram showing an operation example of a track error signal in FIG.

FIG. 12 is a diagram showing the principle of high-density recording in the case of magneto-optical recording according to the present invention.

FIG. 13 is a diagram showing changes in the medium during spot diameter control during recording in FIG.

FIG. 14 is a diagram showing a temperature distribution of the recording / reproducing layer of FIG.

FIG. 15 is a software flowchart of spot diameter control in the microcomputer of FIGS.

FIG. 16 is a principle diagram showing a method of recording a minute signal smaller than the light spot diameter in the conventional example.

FIG. 17 is a principle diagram showing a system in which reproduction can be performed with half or less of a reproduction spot diameter in conventional magneto-optical reproduction.

FIG. 18 is a diagram showing the recording wavelength dependency of a reproduction signal in the conventional system.

[Explanation of symbols]

1 laser light 2 Objective lens 3 discs 4 light spots 12 playback layers 13 recording layer 14 Temperature-dependent variable light transmittance medium (optical shutter layer) 15 Optical recording / reproducing layer 17 Optical head 18 Photodetector signal 19 Micro signal amplification circuit 20 Auto laser power control circuit 21 Recording / playback spot diameter adjustment circuit 22 Waveform equivalent / demodulation circuit 23 Tracking control circuit 24 Focus control circuit 25 System control circuit 28,29 photo detector 30, 31 I-V conversion circuit 32, 33 integrator 34 Phase compensation circuit 35,37 Subtractor 38 amplifier 39 Laser driver 40 laser 41,42 Polarizing prism 44 Signal amplitude detection circuit 45 A-D converter 46 Microcomputer 47,49 DA converter 48-track error signal generation circuit 50 switch 51 Tracking control circuit

Claims (9)

[Claims] 1. A laser beam in an optical disk device for performing recording / reproducing by using reflectance change due to uneven pits formed on an optical disk medium or phase change of a recording material, or for magneto-optical recording / reproducing. In the method of reproducing the signal by condensing the light on the recording medium on the disc surface by the objective lens, at room temperature on the medium layer on which the signal is recorded (on the side where the laser beam is emitted from the objective lens on the disc surface). In this case, the temperature-dependent optical shutter layer is configured to absorb the reproduction laser wavelength, stop absorbing the reproduction laser wavelength due to the temperature rise due to the reproduction laser power, and absorb the reproduction laser wavelength due to the temperature decrease again after passing through the reproduction focused spot. , The temperature-dependent optical shutter layer is formed in the portion that does not absorb the above-mentioned reproduction laser wavelength in the light spot on the medium during reproduction. A high-density recording / reproducing system for an optical disk device, characterized in that a signal is reproduced by reading a change in reflectance or a change in Kerr rotation angle of reproduction reflected light reflected from an underlying recording medium layer and transmitted through a temperature-dependent optical shutter layer. . 2. A laser beam in an optical disk device for recording / reproducing using magneto-optical recording / reproducing by using reflectance change due to uneven pits or phase change of recording material formed on an optical disk medium. In the method of reproducing the signal by condensing the light on the recording medium on the disc surface by the objective lens, at room temperature on the medium layer on which the signal is recorded (on the side where the laser beam is emitted from the objective lens on the disc surface). In this case, a temperature-dependent optical shutter layer that transmits the reproduction laser wavelength, absorbs the reproduction laser wavelength due to the temperature rise due to the reproduction laser power, and transmits the reproduction laser wavelength due to the temperature decrease again after passing through the reproduction focused spot. In the portion that does not absorb the above-mentioned reproduction laser wavelength occupying the light spot on the medium during reproduction,
An optical disk characterized by performing a read signal reproduction by changing the reflectance or the Kerr rotation angle of the reproduction reflected light reflected from the recording medium layer below the temperature-dependent optical shutter layer and transmitted through the temperature-dependent optical shutter layer. High-density recording / reproducing system of the device. 3. The temperature-dependent optical shutter layer, which is reflected from the recording medium layer below the temperature-dependent optical shutter layer in a portion which does not absorb the reproduction laser wavelength in the light spot on the medium during the reproduction, forms a temperature-dependent optical shutter layer. Proportional to the disc reflected light amount obtained from the read signal detector in the optical head so that the average value of the reflected light amount is always constant when reading the signal change of the reflectance or the Kerr rotation angle of the transmitted reproduction reflected light. Based on the average reflected light amount obtained by averaging the photo-current conversion amount, the reproduction laser emission power is controlled to occupy the light reproduction spot on the disk medium, and the reproduction laser wavelength of the temperature-dependent optical shutter layer is set to 3. The high density recording of the optical disk device according to claim 1 or 2, wherein the area ratio of the non-absorbing area is always constant. Playback system. 4. An optical disc formed on an optical disc medium, wherein a laser beam is once converted into heat energy to perform punching type, layer change type, magneto-optical type recording, and the medium layer on which a signal is recorded. A temperature-dependent optical shutter that absorbs the reproducing laser wavelength at room temperature, does not absorb the recording laser wavelength due to the temperature rise due to the recording laser power, and absorbs the recording laser wavelength due to the temperature decrease again after passing through the recording focused spot. The temperature-dependent optical shutter layer of the temperature-dependent optical shutter layer is made to have a higher light transmittance by forming a layer and increasing the focused laser power on the medium disc surface during recording than during reproduction. Thermal energy conversion of laser light is performed in the above-mentioned recording medium layer below, and holes are formed, layer changes, or magneto- A high-density recording / reproducing method for an optical disk device, which is capable of recording. 5. A temperature-dependent optical shutter layer that reflects from a recording medium layer below the temperature-dependent optical shutter layer in a portion of the light spot on the medium that does not absorb the recording laser wavelength at the time of recording is formed. Read the change in the reflectance change of the reflected light at the time of transmitted recording and set the photo-current conversion amount proportional to the disc reflected light amount obtained from the reproduction signal detector in the optical head so that the average value of the reflected light is always constant. By controlling the reproduction laser emission power based on the averaged average reflected light amount, the area ratio of the region that does not absorb the recording laser wavelength of the temperature-dependent optical shutter layer occupying the optical recording spot on the disk medium is always 5. The high-density recording / reproducing system for an optical disk device according to claim 4, wherein the density is kept constant. 6. An information recording layer, which is formed on an optical disk medium, for temporarily converting laser light into heat energy to perform punching type, layer change type, magneto-optical type recording, and a signal recorded thereon. Temperature dependence that absorbs the reproducing laser wavelength on the information recording layer at room temperature, stops absorbing the recording laser wavelength due to the temperature rise due to the recording laser power, and absorbs the recording laser wavelength again after passing through the recording focused spot due to the temperature decrease. In the optical disc having the optical shutter layer,
The medium in which the temperature at which the light transmittance changes in the temperature-dependent shutter layer is lower than the medium temperature at which information can be recorded in the information recording layer is lower. A high-density recording / reproducing system for the optical disk device according to the items 2 and 4. 7. An information recording layer, which is formed on an optical disk medium, for temporarily converting laser light into heat energy to perform punching type, layer change type, magneto-optical type recording, and a signal recorded thereon. A temperature on the information recording layer that absorbs the reproduction laser wavelength at room temperature, stops absorbing the recording laser wavelength due to the temperature rise due to the recording laser power, and absorbs the recording laser wavelength again due to the temperature decrease after passing through the recording focused spot. In an optical disc having a dependent optical shutter layer, the light transmittance change speed of the temperature dependent optical shutter layer is slower than the state change speed for information recording of the information recording layer, at the time of recording, The temperature-dependent optical shutter layer occupies a large portion of the recording laser spot on the disc where the laser light transmittance is high. 5. The optical disk device according to claim 4, wherein a spot smaller than the light spot diameter on the board is recorded on the information recording layer by stopping the irradiation of the recording laser power when the area becomes half or less of the area. High-density recording and reproducing system. 8. In a reproduction-only optical disk device in which uneven pits are formed, during reproduction, after the focus control of the objective lens of the optical head is performed and before the tracking control is performed, the groove crossing signal amplitude in the tracking error signal is applied. 3. The reproducing laser power is varied so as to maximize the value, and the reproducing laser power is fixed when the groove crossing signal amplitude becomes maximum.
The high-density recording / reproducing system of the optical disk device described in the item. 9. A reproduction-only optical disk device having concave and convex pits, during reproduction, after the focus control of the objective lens of the optical head, before the tracking control 2. The optical disk device according to claim 1, wherein the reproduction laser power is varied so that the reproduction signal amplitude by the modulated reflected light becomes the maximum, and the reproduction laser power is fixed at the time when the reproduction signal amplitude becomes the maximum. High-density recording and reproducing system.