JP2650249B2 - Magneto-optical disk playback device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention records information by irradiating a laser beam,
Also, the present invention relates to a magneto-optical disk reproducing method capable of reading.

[Summary of the Invention]

According to the present invention, for example, when reproducing a magneto-optical disk in which information is recorded by irradiating a laser beam while applying a magnetic field, the laser beam to be irradiated is intermittently at least at a period higher than the sample rate of the information. And the non-irradiation time is set longer than the irradiation time. Therefore, the signal level of the information of the signal to be read by setting the power of the irradiation laser beam high can be improved, and the reproduction can be performed while improving the reading accuracy and preventing the deterioration of the recorded information. Become.

[Related Art] In recent years, magneto-optical discs in which information can be rewritten to read-only optical discs that read pit information of concavo-convex formed on a reflective surface of an optical disc from the reflected light are also available. Has been put to practical use.

FIG. 4 is a schematic diagram showing a recording / reproducing method for such a rewritable magneto-optical disk. Numeral 1 denotes a magneto-optical disk in which a perpendicular magnetization film 3 is adhered on a glass substrate 2.

Reference numeral 4 denotes an optical head for irradiating the level light LB to the perpendicular magnetization film 3 of the magneto-optical disk 1. The optical head 4 includes a semiconductor laser element 4a and an objective lens 4b as main components and is not shown. Also, an optical system for detecting various information of the magneto-optical disk from the reflected light of the laser beam, a detector, and the like are built in.

Numeral 5 denotes a magnet arranged to face the perpendicular magnetization film 3, and this magnet 5 is mainly used when recording information on the magneto-optical disk 1 or when erasing written information. You.

Such a magneto-optical disk, when recording information,
For example, the N pole of the magnet 5 is opposed to the disk surface, and the laser beam LB is irradiated while rotating the magneto-optical disk 1 so that the polarity of the perpendicular magnetization film 3 is aligned in one direction and erasing is performed.

Next, for example, when the laser beam LB is irradiated with the S pole of the magnet 5 facing the disk surface, the polarity of the perpendicular magnetization film 3 is inverted only at the time of irradiation.

Therefore, information can be written on the optical disk surface by irradiating the laser light in accordance with the recording data.

Also, at the time of reproduction, if the reflected light is detected while irradiating a laser beam weaker than at the time of recording, a so-called Ker (Ke
by rr) effect, since the polarization plane of the reflected laser light can be detected that is rotated by an angle of ± theta _K by the recording data can be read out recorded data from the detected light.

When data is read from such a magneto-optical disk, the reflected light from the optical disk is extracted by the beam splitter 4c and incident on the second beam splitter 4d by the known optical system described above. The reflected laser beam is split into two by the beam splitter 4d, and the split light is detected by the photodetectors 4e and 4f via an analyzer having a predetermined analyzer angle θA, and the difference component is detected by a differential amplifier. By calculating using 4g, the amount of change in the rotation angle θK of the return light is detected, and the data recorded on the magneto-optical disk is read.

At this time, the output S of the differential amplifier 4g is detected as S = P Sin2 θA · Sin2 θK (1), and the irradiation power (reflection power) P of the emission laser light and the rotation angle θK of the reflection light are generally detected. Is larger, Is improved.

[Problems to be solved by the invention] However, the rotation angle θK of the laser beam due to the Kerr effect
Was very small (0.3 °) and it was difficult to improve C / N.

Conventionally, as a detection method for increasing θK, a P-wave is made incident on a disk by the optical system shown in FIG. 5 and the characteristics of the beam splitter 4C are set such that the S-wave reflectance of the reflected light is 100% and the P-wave reflection is Means for enhancing the rotation angle θK so that the rotation angle θK is substantially increased by attenuating the rate to, for example, 20% are known.

That is, as shown in FIG. 6, when the transmittance of the P-wave component of the reflected laser light is reduced by T SIG and detected through a half mirror that transmits 100% of the S-wave component, only the P-wave component is 1 / It decreases by TSIG, and the rotation angle apparently changes to ± θ'K. Detecting this change differentially at the analyzer angle θA has the effect of further reducing the noise of the synchronization component.

However, in this method, since the overall power P of the reflected light is small, the value of the output signal S cannot be increased, and it has been difficult to substantially improve the C / N.

Therefore, it is conceivable to further increase the laser irradiation power P. However, if the average power of the laser irradiation power P is increased during reproduction, the temperature of the perpendicular magnetization film locally increases,
Signal degradation, that is, a decrease in the rotation angle θK, does not contribute to an improvement in C / N.

That is, as shown in FIG.
The C / N (dB) tends to increase initially when it increases, but it reaches a certain value (approximately 1 mw in a normal example), and when the irradiation power further increases, the temperature of the perpendicular magnetization film rises. Instead, θK decreases and C / N starts to decrease.

This tendency is due to the fact that the linear velocity v of the disc at the time of playback is
...
It can be seen that the rise of the temperature of the perpendicular magnetization film due to the irradiation laser power is a factor that limits the improvement of C / N.

[Means for solving the problem]

The present invention has been made with the object of solving such a problem, and irradiates a laser beam for irradiating a magneto-optical disk intermittently at a sample rate, for example, while suppressing a rise in the temperature of an irradiated surface, and A level of reflected light is detected.

[Action]

For example, the intermittent ratio of the laser beam power output from the laser emission source, that is, the duty is 10% (for example, 20%).
(nSec vs. 200nSec), the temperature rise of the magnetized film on the magneto-optical disk surface can be set to the same value even if the laser power applied during conventional reproduction is increased by a factor of 10. The power level can be up to 10 times higher. Therefore, the detection sensitivity is improved, and the C / N is significantly improved.

[Embodiment] FIG. 1 is a plan view showing an example of the outline of a magneto-optical disk 1 symmetrical to the reproducing method of the present invention, and is an example of a sample servo type disk.

In this figure, T indicates the center of the track, and BA indicates an address byte area (hereinafter, referred to as a servo byte area) formed at predetermined intervals on the track T by embossing or the like in advance.

Further, WA indicates a recording area (data area) following the servo byte area BA. When the recording area WA is irradiated with a laser beam, data can be recorded on the perpendicular magnetization film.

As shown in the enlarged view, in the servo byte area BA, Pa, Pb, and Pc are formed as pits in advance by embossing of unevenness.

Then, as described later, the sampling pulses P1, P2, P
The reference clock signal CCK and the tracking control signal can be detected by detecting these pits Pa, Pb and Pc at the timings of P3 and P5, and the focus error signal and the like are also detected at the timing of the sampling pulse P4. It has been made possible.

Next, the overall structure of an apparatus according to an embodiment which can be employed in the optical disk reproducing method of the present invention will be described in detail with reference to FIG.

In this figure, at the time of recording, data D1 to be recorded from terminal Tin, for example, from a computer or the like via an interface
Is supplied.

The data D1 is sent to the modulation circuit 9 and subjected to a predetermined modulation including bit conversion and the like, and then sent to the laser drive circuit 11. The laser drive circuit 11 is supplied with a control signal in each mode of writing, reading or erasing from the interface, outputs a signal for driving the laser diode 12 of the optical pickup 10 in response thereto, and outputs data. A drive pulse signal having a timing corresponding to a channel clock CCK serving as a reference clock is supplied to the laser diode 12 at the time of recording and erasing, and an intermittent drive signal described later at the time of reading.

The optical pickup 10 includes, in addition to the laser diode 12,
Optical system 13 and A, B, C, D and A ', B', C ', D'
It is provided with two divided photodetectors 14A and 14B and a photodiode 15 for detection.

The photodiode 15 includes the laser diode 12
Is to detect the intensity of the emitted laser light. The photodetectors 14A and 14B detect the reflected light of the laser light from the magneto-optical disk 1 via an analyzer, respectively. For example, when detecting a signal from the magnetization of the Kerr rotation angle θK. On the other hand, one detects the change in the Kerr rotation angle θK as a positive component, and the other detects the change in the Kerr rotation angle θK as a minus differentially.

The motor M is servo-controlled by, for example, a PLL (Phase Locked Loop) by a motor servo circuit MD, and accurately rotates the magneto-optical disk 1 at a predetermined speed (angular speed).

The laser light output from the laser diode 12 is applied to the magneto-optical disk 1 via the optical system 13 and a part of the laser light is incident on the photodiode 15.

Then, the output of the photodiode 15 according to the light intensity of the laser light is supplied to a sample-and-hold (S / H) circuit 18 via a DC amplifier circuit 17. In this S / H circuit 18,
A sample-and-hold operation is performed according to the above-described sample pulse P4, and this output is supplied to the laser drive circuit 11 via an APC amplifier circuit 19 as an APC (Automatic Power Control) control signal. Thus, the light intensity of the laser light output from the laser diode 12 is kept at a predetermined value.

The respective outputs of the photodetectors 14A and 14B of the optical pickup 10 to which the reflected light of the laser light from the magneto-optical disk 1 enters via an optical system 13 are sent to an arithmetic circuit 16, respectively. The arithmetic circuit 16 outputs a light detection signal SA (SA = A + B + C + D + A '+ B') which is a sum signal of the outputs from the respective light receiving regions of the photodetectors 14A and 14B.
+ C '+ D') (including the DC component) is sent directly to the focus servo circuit 21 and the light detection signal SB [SB = (AC-BD) + (A ')
C'-B'D ')] is sent to the focus servo circuit 21 via the S / H circuit 22 which performs a sample and hold operation according to the sample pulse P4. The focus servo control signal generated by the focus servo circuit 21 on the basis of the signals SA and SB is transmitted to the optical pickup.
It is sent to 10 to control the focus.

Further, the light detection signal SC (SC = A
+ B + C + D + A '+ B' + C '+ D') are sent to the peak value detection circuit 51, the S / H circuits 31, 32, 33 and the sampling clamp circuit 41, respectively. The light detection signal SC is
This is a detection signal of a concavo-convex pattern in the pit area BA of the magneto-optical disk 1 described above. The peak value detection circuit 51 detects the peak value of the light detection signal SC, and further, the unique pattern detection circuit 52 detects the peak value of the magneto-optical disk 1.
A pit pattern having an interval uniquely provided only between the upper pits Pb and Pc is detected to detect the pit PC.
Sent to 54. The pulse generation circuit 54 generates a channel clock CCK as a reference clock synchronized with the pit PC based on the detection output obtained by the unique pattern detection circuit 52, and generates a byte clock B
It forms and outputs YC, servo byte clock SBC and various sample pulses P1, P2, P3, P4, P5, and the like. Although not shown, the channel clock CCK is supplied to all circuit blocks. The sample pulses P1 to P3 are S / H
The circuits 31, 32, and 33 are provided.

The sample pulse P4 is supplied to the S / H circuits 18 and 22 and also to the sampling clamp circuit 41. The sample pulse P5 is also used for detecting the moving direction of the optical pickup 10, for example. Further, the peak value detection circuit 51 and the unique pattern detection circuit 52 include:
A gate pulse is supplied from the pulse generation circuit 54.

In each of the S / H circuits 31, 32, and 33, a sample-and-hold operation is performed on the supplied light detection signal SC with the sample pulses P1, P2, and P3. The output from the S / H circuit 31 and the output from the S / H circuit 32 are compared in level by a comparator. This comparison output is sent to a tracking servo / seek circuit 36 and an arithmetic circuit 35
Sent to In the subtraction circuit 35, the comparator 34
A difference signal between the signal from the S / H circuit 33 and the signal from the S / H circuit 33 is formed and sent to the tracking servo / seek circuit 36 as a tracking error signal. The tracking servo / seek circuit 36 performs tracking control and feed control of the optical pickup 10.

The sampling clamp circuit 41 receives the light detection signal SC and the sampling clamp circuit 4.
2 includes a light detection signal SD [SD = (A + B + C + D)-
(A '+ B' + C '+ D')] respectively
It is supplied from 16. The light detection signal S
C is a detection signal of a concavo-convex pattern in the pit area BA of the magneto-optical disk 1 as described above. The light detection signal SD is a detection signal of data written in the data area WA of the magneto-optical disk 1, and is recording data obtained by detecting the rotation angle of the laser reflected light as described above. In each of the sampling clamp circuits 41 and 42, each signal is clamped by a sample pulse and sent to the multiplexer 43. The switching selection operation of the multiplexer 43 is controlled by a control signal from a sync detection / address decode circuit 45. For example, first, the light detection signal SC is applied to the sampling clamp circuit 4.
If it is sent to an analog / digital (A / D) converter 44 via a multiplexer 43 and converted to a digital amount and then sent to a demodulation circuit 46, the output from the demodulation circuit 46 is sync detection / address decoding The signal is sent to a circuit 45 to detect a sync (synchronization signal) and decode address information. Then, according to the address information of the data to be read supplied from the computer or the like via the interface, when the address information matches the actual address, the multiplexer 43 is controlled to be switched, so that the light detection for the data area WA of the disk is performed. The signal SD is sent to the A / D converter 44 and the demodulation circuit 46, and data D0 obtained by performing demodulation processing including bit conversion is output from the output terminal T out. This data D0 is sent to a computer or the like via the interface. When writing data,
A control signal is sent from the sync detection / address decode circuit 45 to the modulation circuit 9, and data to be written from the modulation circuit 9 is sent to the laser drive circuit 11 in response to the control signal.

In the apparatus described above, in the reproducing method of the present invention, a narrow pulse LP as shown in FIG. 3A is formed in synchronization with the clock signal CLK output from the pulse generating circuit 54 at the time of reproduction. Laser drive circuit formed at 55
11 is applied.

The pulse LP controls the laser diode 12 to emit light intermittently.

The pulse width of the pulse LP is, for example, the clock cycle is t0.
(100ns), if it is 1/5 to 1/20, about 20ns to 5n
Set to s. Therefore, such a pulse LP
The average power P av of the laser light modulated by the above becomes extremely small. For example, when the duty of the pulse LP is 10%, even if the peak value power is 10 mw, the average value power can be suppressed to 1 mw.

When the intermittently modulated laser power is reflected from the disk surface and the detection signals corresponding to the data are detected by the photodetectors 14A and 14B from the reflected light whose polarization plane is rotated by the Kerr effect as described above, the signal The waveforms Sa and Sb are output, and a detection signal SD is obtained by subtracting Sa-Sb.

The detection signal SD is held for each sample in the sampling clamp circuit 42, input to the multiplexer 43 as reproduction data of the data area WA, and A / D converted together with the signal of the pit area BA and input to the demodulation circuit. .

Laser diode 12 made of semiconductor is several hundred MHz to several GH
Since it is easy to intermittently emit laser light in response to the pulse of z, extremely high-density sample data recorded on the magneto-optical disk 1 is appropriately irradiated, and reflected light corresponding to the data is detected. It is not difficult.

In addition, even when the recording data is analog information, if the intermittent period t0 of the laser beam is twice or more the maximum frequency, it can be detected without deteriorating the signal.

For example, if the peak power of the signal for both SA and SB is 10 mW, the peak value of the signal is 1 mW of the conventional 1 mW as described above.
Since the value of 0 is obtained, the peak value is reduced to 1/10 by using the enhancement technique of the P-wave together with the peak value of 1 mW, thereby reducing the noise of the in-phase component and enhancing θK. This makes it possible to further improve the C / N of the reproduced data.

〔The invention's effect〕

As described above, the reproducing method of the magneto-optical disk of the present invention controls the laser light to be applied to the disk intermittently at least at least the timing cycle of the clock signal, and sets the irradiation time shorter than the non-irradiation time. By setting, the peak value of the irradiation power is increased while preventing the temperature rise of the magnetic film, so that there is an effect that the C / N of the reproduction detection data can be made higher than before.

Therefore, the quality of the reproduction detection data is improved, and occurrence of erroneous data can be reduced.

[Brief description of the drawings]

FIG. 1 is a plan view of a magneto-optical disk and an enlarged view of a track, FIG. 2 is a block diagram of an entire apparatus to which the reproducing method of the magneto-optical disk of the present invention can be applied, and FIG. FIG. 4 is an explanatory diagram showing an outline of a magneto-optical disk, FIG. 5 is an outline diagram of a recording data detection system, FIG. 6 is an explanatory diagram for detecting rotation of a polarization plane, and FIG. FIG. 4 is a data diagram showing a relationship between C / N and laser power. In the figure, 10 is an optical pickup, 11 is a laser drive circuit, 12
Denotes a laser diode, 13 denotes an optical system, 14A and 14B, and photodetectors, and 54 denotes a pulse generation circuit.

Claims (1)

(57) [Claims] 1. A method for reproducing a magneto-optical disk having predetermined data recorded on a magnetized film by irradiating a laser beam, the method comprising: The laser beam is set so as to be higher than the average power level set for the magnetic film of the magneto-optical disk, and the laser beam is modulated by a pulse signal having a predetermined sampling period. Setting the duty ratio of the pulse signal so that the laser power does not exceed the average power level for reproduction, and reproducing the predetermined data recorded on the magnetized film of the magneto-optical disk. Magneto-optical disk reproduction method.