JP2001351244A - Optical disk device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical disk device capable of optimizing the substantial spot size, even in a state in which recording pit is not formed. SOLUTION: By controlling the output of a light source with the level of a tracking error signal generated on the basis of a signal showing the light quantity of a reflected light becoming maximum in laser beam 1 projected to the optical disk, which is provided with a second medium layer 14 having the transmissivity with respect to the laser beams 1 from the light source being changed dependent upon the temperature and not transmitting the laser beam on one side of the border of the specific temperature, on a first medium layer 15 recording the information as a pit, the size of the spot (substantial spot) which is formed by the part transmitting the second medium layer 14 among the laser beam is controlled, so as to become the optimum size with respect to the track pitch of a pit train recorded on the first medium layer 15.

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 an optical disk.

[0002]

2. Description of the Related Art FIG. 16 is a principle diagram showing a method of recording a small signal smaller than a 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 disk, 4 is a light spot condensed by the objective lens 2, 5 is a temperature distribution on the disk medium, 6 is a Curie for performing magneto-optical recording, for example. A recordable temperature 7 corresponding to the temperature is a minute signal to be recorded.

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

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

In order to increase the density of a magneto-optical disk, it is necessary to establish both a recording technique and a reproducing technique.
For recording, the temperature near the center is the highest in the light spot created by the laser on the disk 3 in FIG. Therefore, since the temperature near the center easily reaches the recordable temperature, if the Curie temperature of the recording material is set to a temperature corresponding to the central portion of the light spot 4, recording smaller than the light spot diameter such as the minute signal 7 is performed. A spot can be formed. Therefore, in recording, high-density recording becomes possible by shortening the laser irradiation interval while partially overlapping the light spots.

On the other hand, in reproduction, the wavelength of the laser is λ, and the numerical aperture of the objective lens 4 of the optical pickup is NA.
(Coefficient determined by lens diameter and focal length)
The reproduction limit wavelength is determined by λ / 2NA. For example, in the current optical disk device, λ = 780n
Since m and NA = 0.5, the detection limit is about 0.78 μm.
m. Thus, when the wavelength of the laser to be used is determined, the practical numerical aperture NA of the objective lens is almost fixed, and thus the detection limit is physically or optically determined. Therefore, 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 practical use of a red semiconductor laser and SHG (2
The development of green and blue lasers using harmonic generation elements) is progressing.

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

In this method, the recording layer 13 shown in FIG.
Is made to have a large coercive force, and the reproducing layer 1 shown in FIG.
2 has a small holding force. At this time, by applying an initialization magnetic field before reproduction, the magnetization directions of the reproduction layer 12 near the detection signal are all reversed in one direction and erased. Next, by irradiating the reproducing layer 12 with the reproducing laser beam to the reproducing layer 12 which has been erased in one direction as described above, only the high-temperature portion of the reproducing layer 12 is heated above the Curie point, and the magnetic layer recorded on the recording layer 13 is heated. The information is transferred, and a small signal is detected.

As described above, apparently, the light spot area is reduced, and the same effect as when the light spot diameter is practically reduced can be obtained. Reproduction with a recording wavelength shorter than half the wavelength, for example, 0.78 μm, becomes possible, and the resolution is improved twice or more.

However, in practice, the area of the light spot 4 irradiated on the board surface is not reduced, and therefore, the medium noise caused by the non-uniformity of the magnetization and the reflectivity of the medium included in the reproduced signal, etc. Is the same as in the conventional magneto-optical reproducing method using the original large light spot as it is. On the other hand, the reproduced signal level is reduced by the amount that the magnetic information area in the reproduction layer 12 transferred from the recording layer 13 is smaller than the area of the light spot 4 on the board.

Therefore, the higher the recording density, the more
Since the ratio of the area contributing to signal reproduction to the surface light spot area becomes smaller, it is natural that the S / N of the reproduced signal becomes smaller.

[0012]

The high-density recording / reproducing method in the conventional optical disk apparatus has been performed according to the above principle. However, there is a problem that the ratio of the area which contributes to the reproduction signal becomes small, and the S / N of the reproduced signal becomes small. Also, because magnetic transfer is used,
It can be applied only to the magneto-optical recording / reproducing method.
There is also a problem that the above-described method is applied to the same reproduction-only method as that of the D player or the like, and the density cannot be increased.

Further, in the above-mentioned method, a substantial spot diameter must be determined due to a difference in temperature rise of the disk medium due to the light spot, and temperature management on the medium is required. Since it is not easy to detect the temperature at the light spot position, it is very difficult to control the laser power.

Further, when the recording density in the track pitch direction is increased to increase the recording density, the track pitch becomes extremely small with respect to the light spot diameter. Due to such a problem that a tracking signal cannot be obtained, there has been a problem that tracking cannot be performed well.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems. In addition to being able to increase the density without deteriorating the signal S / N, it is also possible to accurately control the substantial light spot diameter and It is an object of the present invention to provide an optical disk device and an optical disk capable of realizing high-density recording and reproduction that can be used only for reproduction or a phase change method.

[0016]

According to the present invention, there is provided an optical disk apparatus for reproducing information by scanning an optical disk with a spot of a laser beam, and a light source for irradiating the laser beam and recording the information as pits. A second medium layer that does not transmit the laser light is provided on one side of the first medium layer in which the transmittance for the laser light changes depending on the temperature and one side of the first medium layer is separated from a predetermined temperature. An optical disc, and light detection means for detecting a light quantity reflected from the optical disc among laser lights emitted from the light source to the optical disc, and outputting a signal indicating a reflected light quantity as a detection result, Means for receiving the output of the light detection means and generating a tracking error signal; and controlling the light source so that the level of the tracking error signal is maximized. By controlling the force, the size of the spot formed by the portion of the laser light that passes through the second medium layer is optimized for the track pitch of the pit row recorded on the first medium layer. And control means for controlling the size.

According to a second aspect of the present invention, in the optical disk device according to the first aspect, the control means for controlling the output of the light source includes an amplitude detecting means for generating a signal indicating the amplitude of the tracking error signal; An A / D converter for inputting the signal indicating the amplitude, and a microcontroller for determining a command value for controlling the output of the light source using amplitude information obtained by A / D conversion by the A / D converter. A computer; and a light source output control system that drives the light source based on the command value.

According to a third aspect of the present invention, in the optical disk apparatus according to the first aspect, the control of the light source output by the control means includes the step of controlling the tracking error signal after performing the focus control and before performing the tracking control. It is characterized by being performed using.

[0019]

According to the first aspect of the present invention, the output of the light source is controlled so that the level of the tracking error signal is maximized, so that the laser light is formed by a portion that transmits through the second medium layer. The size of the spot (substantial spot) to be controlled is controlled so as to be optimal with respect to the track pitch of the pit row recorded on the first medium layer. The size of the substantial spot can be optimized.

Further, according to the second aspect, by performing the tracking operation after adjusting the output (laser power) of the light source, the adjustment processing for optimizing the effective spot diameter is performed based on the tracking error signal. Can do it.

[0021]

[Embodiment 1] FIG. 1 shows an embodiment of the present invention.
FIG. 3 is a cross-sectional view of an optical disk used in the optical disk device. In the figure, reference numeral 15 denotes an optical recording / reproducing layer (first medium layer) formed on a substrate of an optical disk (not shown). This layer 15 is a recording / reproducing layer for information recorded / reproduced as pits on unevenness, recorded / reproduced using a change in reflectance due to a phase change of a recording material, or magneto-optical recording / reproduced. 14 is made of a material such as a polymer material, for example, absorbs light of a specific laser wavelength at normal temperature, and stops absorbing the light of the specific laser wavelength with a rise in medium temperature, and at the same time, absorbs light of the specific laser wavelength. This is a temperature-dependent transmittance changing medium (second medium layer) in which the light transmittance increases, the medium temperature decreases again, and the light of the specific laser wavelength is absorbed.

FIG. 3 schematically shows a change in the medium during reproduction of the optical disk used in the optical disk device according to the embodiment of the present invention. FIG. 4 shows a timing chart of the medium change in FIG.

FIG. 5 is a configuration diagram of an optical disk device in 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,
19 is a small 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 ".

Reference numeral 21 denotes a recording / reproducing spot diameter adjusting circuit for controlling the recording / reproducing spot diameter based on the output of the small signal amplifying circuit 19, and a reference for the automatic laser power control circuit 20; A waveform equalization / demodulation circuit for waveform-equalizing and demodulating the recording / reproducing information output from the optical disc; a tracking control circuit for tracing a light spot from the objective lens 4 into a guide groove of a disk; A focus control circuit for causing the light spot from 4 to follow the surface deviation of the disk; 25, a system control circuit for comprehensively controlling systems such as tracking control, focus control, disk rotation control, and laser power control;
Reference numeral 6 denotes an output of the waveform equalization / demodulation circuit.
Is an actuator drive signal for moving the objective lens 4.

FIG. 6 shows parts 20, 21, 17, 19 constituting a recording / reproducing spot diameter adjusting system according to an embodiment of the present invention.
FIG. 4 is a more detailed block diagram of FIG. In the figure, 30,
Reference numeral 31 denotes an IV conversion circuit for performing IV conversion of the outputs of the photodetectors 28 and 29 to convert the output into voltage information, and 32 integrates the output of the IV conversion circuit 30 and averages reflected light from the disk. Is an integrator for calculating the average laser output power based on the output of the detector 29 which monitors the light output power from the laser 40.

Reference numeral 34 denotes a laser power control loop for controlling the average laser output power based on the output of the detector 29 for monitoring the light output power from the laser 40, and a phase compensation circuit for maintaining stability and responsiveness. , 3
5 is an apparent light spot diameter command value 36 and an integrator 32
Subtracter for calculating the spot diameter error by subtracting the calculated value of the average reflected light from the disk, which is the output of
Reference numeral 7 denotes a subtractor for giving a reference to the laser power control loop and generating a laser power error signal. 38
Is an amplifier for amplifying the output of the subtracter 37 for producing a laser power error signal. 39 is a driver for driving the laser 40, and 41 and 42 are polarizing prisms (beam splitters) arranged in the optical head 17.

FIG. 7 is a block diagram for controlling the apparent spot diameter so that the reproduced signal amplitude becomes maximum.
In the figure, reference numeral 44 denotes a signal amplitude detection circuit composed of an envelope detector or the like; 45, an A / D converter for converting the output of the signal amplitude detection circuit 44 from analog to digital; and 47, an optimal output based on the output of the microcomputer. It is a digital-analog converter (DA converter) for adjusting the spot diameter.

FIG. 8 is a block diagram for controlling the apparent spot diameter so that the amplitude of the tracking error signal is maximized. In the figure, reference numeral 48 denotes a track error signal generation circuit for generating a track error signal based on light reflected from a disk; 49, a DA converter for applying a control voltage for operating an actuator; 50, a changeover switch; This is a tracking control circuit for causing a light spot to trace the groove.

FIG. 9 is a diagram showing the open loop characteristics of the control system in the block diagram of FIG. 7 or FIG. FIG. 10 shows how the medium changes when the spot diameter control in FIGS. 7 and 8 is performed during reproduction. FIG. 11 is a diagram showing a timing chart in FIG.

FIG. 12 shows how the medium changes when the spot diameter control 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 a temperature distribution of the recording / reproducing layer of FIG.

FIG. 15 is a software flowchart of the spot diameter control system in the microcomputer shown in 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 light transmittance variable medium formed on an optical recording / reproducing layer (object lens side). is there. The temperature-dependent light transmittance variable medium is formed of, for example, a polymer material or an organic material, and has a material having a light transmittance higher in a high temperature region with respect to the medium temperature as shown in FIG. It is.
The change in the transmittance may be due to a change in the regularity of molecular arrangement such as a liquid crystal material in which the light transmittance is increased by melting of the material. In addition, TeOx (Ge) and TeOx (S
n) The light transmittance may be changed by crystallization of a film or, for example, a chalcogenide attached in an amorphous state by heating and cooling. However, the above-mentioned temperature-dependent light transmittance variable medium can maintain a stable state and a metastable state at room temperature as developed in a general optical recording medium, and can reversibly shift to each state. Such a structure is not necessary, and any material may be used as long as the state of the material changes at 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 reproducing laser power is controlled at the time of reproducing to control the medium temperature in the light spot and in the vicinity thereof, FIG. As shown in FIG. 3, the substantial reproduction spot diameter can be made smaller than the apparent diameter of the light spot diameter. In general, when the optical disk is rotating, the medium temperature near the light spot becomes higher on the rear side in the traveling direction of the light spot and lower on the front side, as described in the conventional example. .
This is because the light energy storage time is longer in the rear of the light spot. Therefore, the light transmittance increases in the high-temperature area (white area) in the light spot 4 in FIG. 3 (detection area 11), and it becomes possible to read the hatched recording mark 9 located therein. .

Therefore, as shown in FIG. 3, the light transmittance of the temperature-dependent light transmittance variable medium is increased in the region where the medium temperature is high, and the reflected light of the recording / reproducing layer is transmitted to the objective lens only in the region where the transmittance is high. It is possible to return to. If a light transmittance variable medium having the opposite temperature dependency is used, the light transmittance of the three-month low-temperature portion of the light spot 4 in FIG. 3 increases.

Generally, if the recorded mark (pit) has a pit diameter of less than half of the reproducing light spot,
It is impossible to regenerate. However, in the case of FIG. 3, the region where the medium temperature is high and the light spot 4
Since only the region where the light spot 4 overlaps is involved in the reproduction, the substantial reproduction spot diameter can be made sufficiently smaller than the apparent diameter of the light spot 4. Thus, for example, it is possible to reproduce even a recording pit having a half or less of an apparent light spot diameter as shown in FIGS.

In the method of transferring magnetism shown in the conventional example, the diameter of the light spot can be reduced substantially, but all the reflected light of the light spot on the medium involved in the reproduction signal is used. On the other hand, in this system, in a region where the medium temperature not involved in reproduction is not so high, light is absorbed (light transmittance is low).
Does not contribute much to the playback signal.

However, in the prior art, the smaller the substantial light spot diameter, the smaller the ratio of the amount of reflected light related to the reproduction signal to the light reflected from the medium, and the output of the reproduction signal decreases. . At this time, since the light spot naturally reflects from the medium in all areas, the medium noise due to the surface properties of the medium and minute variations in the material remains constant. Therefore, it is natural that the S / N (noise relative to the signal output) of the reproduction signal deteriorates as the substantial light spot diameter decreases.

In this system, the reflection of the signal from the recording / reproducing layer occurs only in the region where the medium temperature is high. Therefore, even if the light spot diameter is substantially reduced, the reproduced signal output is reduced. At the same time, the reflection of light from a portion unrelated to signal reproduction is reduced, so that the noise level due to the medium is also reduced, and the substantial light spot diameter is reduced without significantly deteriorating the S / N of the reproduction signal. can do.

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

FIG. 4 shows the relationship between the change in medium characteristics during reproduction and the reproduction laser power in the embodiment of the present invention. When the disk is rotated and the light spot is scanned at a certain linear velocity, the reproduction laser power is gradually increased. Also, while the medium transmittance of the temperature-dependent light transmittance variable medium increases, the medium transmittance does not increase unless the laser power is relatively increased in the front part. for that reason,
For example, when reproducing an optical disk having recording pits less than half of the reproduction light spot 4, the light transmittance of the temperature-dependent light transmittance variable medium at the rear part in the light spot in FIG. 4 is high and low at the front part. If the reproduction laser power is set at a predetermined value, the actual reproduction spot diameter matches the recording pit diameter at a predetermined laser power in the figure, and a reproduction signal output can be extracted as shown in FIG.

In the present invention, as described above, even if the temperature-dependent light transmittance variable medium is configured so that the light transmittance increases at a high temperature and decreases at a low temperature, the temperature-dependent light transmittance varies. The same effect can be obtained even if the medium composition is configured such that the light transmittance of the medium decreases at high temperature and increases at low temperature. However, at this time, it is needless to say that the substantial light spot shape is an area outside the detection area 11 in the light spot shown in FIG. Accordingly, 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 set accurately, the diameter of the light spot can be determined accurately. This is the same in the conventional method of performing magnetic transfer. However, in the conventional case, there is no means to measure the temperature distribution on the medium,
Laser power could not be controlled. For this reason, there has been a problem that the medium temperature at the time of reproduction varies due to a change in the medium temperature due to a change in the environment inside the apparatus or at room temperature, and the substantial light spot diameter fluctuates. The substantial change in the light spot diameter described above not only deteriorates the signal output in high-density signal reproduction, but also causes the signal reproduction to be impossible in some cases.

However, in the embodiment of the present invention, since the light transmittance of the optical disk medium changes, the region of the temperature-dependent light transmittance variable medium having a high light transmittance in the portion where the light spot shines is The light spot 4 depends on the ratio of the light spot 4 to the total area.
Changes the total light reflectance. For example, when the medium is configured such that the temperature-dependent light transmittance variable medium has a high light transmittance at a high temperature and a low light transmittance at a low temperature, a portion having a high light transmittance involved in signal reproduction has a lower portion. Although the light is reflected by the recording / reproducing layer, the light is absorbed in a portion that does not participate. Therefore, if the total light reflectance of the light spot 4 is measured, the temperature-dependent light in the portion where the light spot is hit is measured. It is possible to detect how much a region having a high light transmittance in the variable transmittance medium occupies the entire area of the light spot 4.

Therefore, when the optical disk apparatus is configured as shown in FIG. 5, after the output of the photodetector for detecting the light reflected from the disk is amplified by the small signal amplifier circuit 19, the recording / reproducing spot diameter adjusting circuit By controlling the reference of the automatic laser power control circuit by 21, it is possible to control the laser power so that the light reflected from the disk is always constant. In this way, if control is performed so that the amount of reflected light from the disc during reproduction is always constant, that is, the region where the light spot of the present invention hits the high light transmittance area in the temperature-dependent light transmittance variable medium, It is possible to keep the ratio of the light spot 4 to the entire area constant at all times, and to control the actual reproduction spot diameter (for example, the region of the light spot 4 where the light transmittance of the temperature-dependent light transmittance variable medium is high). Becomes possible.

Such a recording / reproducing spot diameter adjusting system is specifically configured as shown in FIG. 6, for example. Laser 4
A part of the light emitted from 0 is split by the polarizing prism 41 to the light detector 29. This split light is I-
The V conversion circuit 31 detects what kind of laser power is currently being emitted. The actual light may be optically modulated, for example, at the time of recording, and is input to the integrator 33 to extract the average laser emission power.

Next, in order to maintain the responsiveness and stability of the automatic laser power control loop, the average laser emission power is input to the phase compensation circuit 34, and the output thereof is subtracted by the subtracter 37.
After comparing with the laser power set value and calculating a deviation from the set value, this error is amplified and supplied to the laser 40 as a drive current by the laser driver 39. In this way, a laser power control loop is formed,
It is controlled so that the laser always emits according to the laser power set value.

Here, the output of the photodetector 28 is converted into the voltage value of the reflected light information of the optical disk by the IV conversion circuit, and is taken out as the average value of the reflected light amount of the disk by the integrator 32. The average value of the amount of reflected light is equal to the value of the light spot 4
Is the total light reflectance of the light-spot 4 in the temperature-dependent light-transmittance variable medium in the portion where the light spot is illuminated. Therefore, the value corresponds to the substantial reproduction spot diameter described above.

Therefore, by comparing the apparent light spot diameter command value 36 in FIG.
After calculating by the subtractor 35 how much the spot diameter deviates from the command value, if this is given as a control command value (reference) of the laser power control loop, the apparent light spot diameter size The laser power can be controlled so that is always equal to the command value. The control band of this light spot diameter adjustment loop is
As can be seen from the open loop characteristics of FIG. 9, the control band is set sufficiently lower than the control band of the automatic laser power control loop. By configuring the integrator 32 of FIG. The open loop gain in the region is secured, and at the same time the stability is secured.
In this way, the laser power can be stably adjusted. That is, the apparent light spot diameter can always be kept 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 variable light transmittance medium.

Next, the apparent spot diameter command value 3
How to set the optimum value of No. 6 will be described. FIG. 7 shows that the amplitude of the reproduced signal is maximized.
This is an example of a method of changing an apparent light spot diameter command value, and a light detector 28 for detecting light reflected from a disk.
After passing through the IV converter 30, the output is input to the waveform equivalent circuit 22 and subjected to signal processing as a reproduced signal 26. The reproduced signal 26 after this waveform equalization is enveloped by the signal amplitude detection circuit 44. The signal amplitude information is detected by A /
The data is converted from analog to digital by the D converter 45 and input to the microcomputer 46.

At this time, first, as a system of the entire apparatus,
After the optical disk is rotated and an appropriate spot diameter command value is given to the laser power control circuit, the focus servo is operated on the objective lens to make the disk surface follow the deviation of the disk surface, and the light spot is tracked to the disk guide groove. So, the tracking servo must be on. In this state, the optimum spot diameter command value which is the output of the DA converter 47 is shifted to, for example, a slightly larger value by the microcomputer algorithm based on the output of the AD converter 45 in FIG. At this time, if the amplitude of the reproduced signal is slightly reduced, the optimum spot diameter command value is shifted to a slightly smaller value. In this way, the optimum spot diameter command value at which the reproduction signal amplitude becomes maximum is searched for, and the change of the optimum spot diameter command value is stopped at the point where 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 tracking control of a VTR and the like. For example, when reproducing a disk recorded with half the recording pits with respect to the light spot 4, the diameter of the light spot 4
If the diameter of the light spot becomes almost the same as the diameter of the recording pit, the signal amplitude will be maximum, and if the diameter is further reduced, the amount of reflected light from the disk will decrease. The reproduction signal amplitude becomes smaller.
Therefore, it is possible to search for the optimum spot diameter by using the hill-climbing method.

The reproduced signal used at this time is the equivalent circuit 22
If the recording / reproducing signal is an analog FM-modulated signal, a signal obtained by extracting a carrier component of the FM signal with a band-pass filter may be used as a signal amplitude. It may be input to the detection circuit 44.

In the above, the means for optimizing the substantial light spot diameter by using the reproduction signal has been described. However, even when recording pits are not formed, such as during recording, the above-described substantial light spot diameter is obtained. In some cases, means for optimizing the diameter may be required. In this case, as shown in FIG. 8, there is a method of optimizing the substantial light spot diameter so as to maximize the amplitude of the tracking guide groove traversing signal.

In FIG. 8, a tracking error is generated by a track error signal generating circuit 48 based on the output of a photodetector 28 for detecting the reflected light from the disk. At this time, even if the tracking method is a push-pull method,
It goes without saying that the tracking error can be similarly detected even in the three-beam system.

The tracking error signal obtained as described above is obtained from the optical disc drive as shown in FIG. 11 when the objective lens in the optical head is operating only the focus servo and the tracking servo is not operating. The tracking error signal is modulated by the signal crossing the guide groove of the track due to the eccentricity. In the configuration shown in FIG. 8, when the objective lens 2 is moved by the actuator in the cross direction of the track by the DA converter 49 based on the instruction of the microcomputer 46, the tracking error signal is modulated by the guide groove regardless of the eccentricity of the disk. Needless to say.

Therefore, as described above, the objective lens 2 is moved by the actuator in the cross direction of the track by the DA converter 49 based on the instruction of the microcomputer 46, and the guide groove is added to the tracking error signal regardless of the eccentricity of the disk. The crossing is caused, and the signal amplitude detection circuit 44 detects the amplitude of the modulation signal of the tracking error signal due to the crossing of the guide groove.

Next, the amplitude of the tracking error signal modulated by the A / D converter 45 is converted into an optimum light spot diameter output from the A / D converter 47 by an algorithm in a microcomputer 46 as shown in FIG. While changing the command value, the amplitude of the modulated tracking error signal is maximized as shown in FIG. At the point where the amplitude of the modulated tracking error signal is maximized, if it is operated to stop the change of the optimum light spot diameter command value, as in information recording, etc.
The optimum spot diameter can be automatically set even in an area where no reproduction signal is recorded.

In the push-pull tracking signal detection method for obtaining the optimum spot diameter using the tracking error signal as described above, the density is not only increased in the line direction but also in the track pitch direction. It can also be seen that, even when this operation is performed, the substantial light spot is automatically adjusted so as to have the 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, by controlling the laser power optimally, the transmittance change area of the temperature-dependent light transmittance variable medium and the light spot 4 overlap. It is possible to precisely control the size of the region (substantial light spot).

In the optical disk according to the present invention, since the change in the transmittance of the temperature-dependent variable light transmittance medium is caused by the change in the temperature of the medium, the thermal energy of the condensed laser light is used to transfer information onto the optical disk. In an optical disc device that performs recording, a time required for temperature rise and a variable transmittance temperature are set according to the heat capacity of the medium, and a laser beam is irradiated at a temperature necessary for recording in the optical recording / reproducing layer, whereby high-density light is emitted. Recording becomes possible.

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 conditions are set so that the heat capacity of the temperature-dependent variable light transmittance variable medium (the optical shutter layer in FIG. 12) is larger than that of the recording medium, a pulse-like shape as shown in FIG. When the recording laser is irradiated, the high-temperature area (area with high light transmittance) of the optical shutter layer = (substantial recording spot) is sufficiently smaller than the light spot 4.

As shown in FIG. 13, the temperature of the lower recording / reproducing layer having a small heat capacity rises more rapidly than the temperature of the optical shutter layer having a large heat capacity. The temperature is reached and recording can be performed. On the other hand, the optical shutter layer gradually widens the high-temperature region, and the substantial light spot gradually increases. However, if the irradiation of the recording laser power is stopped before the substantial high-temperature region in the optical shutter layer becomes large, small recording pits are formed by the laser light that passes through the small light transmittance region in the optical shutter layer. be able to.

At this time, in the above-described method, since the light reflection from the disk during recording can be monitored and the substantial light spot diameter control shown in FIG. 6 can be performed simultaneously, the recording pit diameter during recording can be reduced. Adjustments are also possible. In addition, as can be seen from the temperature distribution in FIG. 14, the temperature distribution due to the conventional light spot is a Gaussian distribution, whereas in the present embodiment, the laser light is emitted only in a portion where the light transmittance of the optical shutter layer is high. Therefore, only the recording pit can have a high temperature distribution. At this time, if a heat insulating layer is inserted between the optical shutter layer and the recording / reproducing layer, it goes without saying that the temperature of only the recording pit can be increased.

Conventionally, changes in room temperature and in-apparatus temperature,
There have been problems such as a change in the diameter of the recording pit and an unstable edge of the recording pit due to a variation in the composition of the medium. However, as described above, in this embodiment, 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 using the tip of a Gaussian temperature distribution.

[0065]

According to the first aspect of the present invention, by controlling the output of the light source so that the level of the tracking error signal is maximized, the portion of the laser beam that passes through the second medium layer is controlled. Is controlled so that the size of the spot (substantially spot) formed by the above becomes the optimum size with respect to the track pitch of the pit row recorded on the first medium layer. However, the size of the substantial spot can be optimized.

Further, according to the second aspect, by performing the tracking operation after adjusting the output (laser power) of the light source, the adjustment processing for optimizing the effective spot diameter is performed based on the tracking error signal. Can do it.

[Brief description of the drawings]

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

FIG. 2 is a diagram illustrating a relationship between a medium transmittance and a medium temperature in FIG. 1;

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

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

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

FIG. 6 is a configuration diagram of a light spot diameter adjusting system according to an embodiment of the present invention.

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

FIG. 8 is a block diagram for controlling an apparent spot diameter so that a tracking error signal amplitude becomes maximum.

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

FIG. 10 is a diagram showing a state of a medium change when the spot diameter control in FIGS. 7 and 8 during reproduction is performed.

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

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

FIG. 13 is a diagram illustrating a change in the medium during spot diameter control during recording in FIG. 12;

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 microcomputers of FIGS. 7 and 8;

FIG. 16 is a principle diagram showing a method for recording a small signal smaller than a light spot diameter in a conventional example.

FIG. 17 is a principle diagram showing a method 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 illustrating the recording wavelength dependence of a reproduced signal in a conventional method.

[Explanation of symbols]

1 laser beam, 2 objective lens, 3 disc,
4 light spots, 12 reproducing layers, 13 recording layers, 1
4 temperature-dependent light transmittance variable medium (optical shutter layer),
15 optical recording / reproducing layer, 17 optical head, 18 photodetector signal, 19 small signal amplifying circuit, 20 auto laser power control circuit, 21 recording / playback spot diameter adjusting circuit, 22 waveform equivalent / demodulating circuit, 23 tracking control circuit, 24 focus control circuit,
25 system control circuit, 28, 29 photodetector, 30, 31 IV 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 D / A converter,
48 track error signal generation circuit, 50 switch, 51 tracking control circuit.

Claims (3)

[Claims] 1. An optical disc apparatus for reproducing information by scanning an optical disc with a spot of a laser beam, comprising: a light source for irradiating the laser beam; and a laser beam on a first medium layer on which information is recorded as pits. An optical disc provided with a second medium layer that does not transmit the laser beam on one side of a predetermined temperature as a boundary, and a laser beam emitted from the light source to the optical disc. Light detecting means for detecting the amount of light reflected from the optical disc, and outputting a signal indicating the amount of reflected light as a detection result, receiving the output of the light detecting means and generating a tracking error signal Means for controlling the output of the light source so that the level of the tracking error signal is maximized. Control means for controlling a size of a spot formed by a portion transmitting through the second medium layer to an optimum size with respect to a track pitch of a pit row recorded on the first medium layer. An optical disc device characterized by the above-mentioned. 2. A control means for controlling the output of the light source includes: an amplitude detection means for generating a signal indicating the amplitude of the tracking error signal; an A / D converter for inputting the signal indicating the amplitude; A microcomputer for determining a command value for controlling the output of the light source using amplitude information obtained by A / D conversion by a D converter, and a light source output control system for driving the light source based on the command value The optical disk device according to claim 1, further comprising: 3. The control of the light source output by the control means,
2. The optical disk device according to claim 1, wherein after performing focus control and before performing tracking control, the tracking is performed using a tracking error signal.