JP2778652B2 - Reproduction method of magneto-optical recording medium - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a reproducing method for a magneto-optical recording medium.

2. Description of the Related Art A method of recording data on a magneto-optical recording medium includes a pit position recording in which information is stored in the presence or absence of a pit and recording is performed by changing a pit interval, and a pit length recording in which information is provided in the pit length. is there. Conventionally, the recording medium recorded by any recording method changes the magnetization direction of the recording medium according to data, and utilizes the magnetic Kerr effect or the Faraday effect generated by the difference in the magnetization direction. That is, the recording medium is irradiated with linearly polarized laser light having a predetermined intensity, and the reflected light whose polarization plane has been rotated by the magnetic Kerr effect or the Faraday effect is detected by the photodetector via the analyzer. Therefore, the amount of light passing through the analyzer changes due to the difference in the rotation angle of the polarization plane of the reflected light, and the change in the amount of light is converted into an electric signal by the photodetector to reproduce the recorded data.

Problems to be Solved by the Invention When data is recorded on a magneto-optical recording medium at a high density, the interval between recording pits becomes narrow, and the amplitude of a reproduced signal decreases. This is because the light spot diameter of the light emitted from the optical head becomes a finite value due to restrictions of each element included in the optical head such as the wavelength of the laser diode and the numerical aperture of the objective lens. The amplitude of the obtained reproduced signal is significantly reduced. Here, the amplitude (intensity) of the reproduced signal is represented by S,
The output light intensity of the laser diode is I, the reflectance of the recording medium is R, the Kerr rotation angle is θ _k , and the MTF (Modulation Transfer Funct
ion), the intensity S of the reproduced signal can be expressed by the following equation.

S∝I · R · θ _k · α According to the above formula, when performing high-density recording on a recording medium, use a laser diode with a short wavelength to reduce the reduction rate α or select an appropriate recording medium. By the above R
And increasing the intensity S of the theta _k value is increased to a reproduction signal can be. However, if the value of I is uniformly increased in order to further increase the intensity S of the reproduction signal, the temperature of the recording medium rises due to the light emitted from the laser diode of the optical head.
The recording pit may be damaged.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a reproducing method for a magneto-optical recording medium capable of increasing the intensity of a reproduction signal from a recording medium without causing damage to recording pits.

Means for Solving the Problems The present invention outputs a drive current of a laser diode for obtaining a servo signal and reproduces a pulse current of a predetermined cycle when reproducing data recorded on a magneto-optical recording medium. Adding the drive current and the pulse current to each other, applying the added drive current and the pulse current to a laser diode as a drive current for reproduction, and irradiating light emitted from the laser diode to the magneto-optical recording medium. Then, the reflected light generated by the reading is read, a reproduction signal representing the data is obtained, and the reproduction processing of the data recorded on the magneto-optical recording medium is performed.

Further, a reproduction signal representing data read from the magneto-optical disk is sampled in synchronization with the output of the pulse current, and a reproduction process of data recorded on the magneto-optical recording medium is performed using a value of the reproduction signal obtained by the sampling. Is preferably performed.

According to the present invention, at the time of reproducing data recorded on a magneto-optical recording medium, a drive current of a laser diode for obtaining a servo signal and a pulse current of a predetermined period are output, and these currents are added. ing. Using the added current as a drive signal for the laser diode, the reflected light of the magneto-optical recording medium generated by the emitted light of the laser diode is read to obtain a reproduction signal representing the recorded data. This reproduction signal is sampled in synchronization with the output of the pulse current, and the reproduction of recorded data including digital signal processing such as digitization and encoding is performed using the obtained sampling value.

FIG. 1 is a block diagram showing a reproducing apparatus for a magneto-optical recording medium, for example, a magneto-optical disk. 2 and 3 show recording pits, a reproduction laser beam and a reproduction RF signal of a magneto-optical recording medium. FIG. 2 shows pit length recording and FIG.
The figures each show a pit position record.

The reproducing apparatus includes a sampling clock pulse generation circuit 11 that outputs a sampling clock pulse of a predetermined cycle. The output of the sampling clock pulse generation circuit 11 is controlled by the controller 10. Sampling clock pulse generator 11
Is supplied to an APC (Automatic Power Control) circuit 12, an adding circuit 14, a first delay circuit 31, and a second delay circuit 32, respectively.

The optical head 20 includes a monitoring photodiode 21, a laser diode 22, and a reproducing photodiode 23 for receiving light reflected from a magneto-optical disk (not shown). A laser beam for recording data reproduction is emitted by the laser diode 22 and irradiates the magneto-optical disk. The reflected light of the recorded data reproducing laser beam from the magneto-optical disk is received by the reproducing photodiode 23 and output as a reproduced RF signal. The monitoring photodiode 21 monitors the emitted laser light so that the amount of light emitted from the laser diode 22 becomes constant. A signal representing the amount of emitted light received by the monitoring photodiode 21 is given to the APC circuit 12.

The APC circuit 12 includes a reference voltage generation circuit 13,
The reference voltage generation circuit 13 generates a reference voltage. APC
The circuit 12 receives the output signal of the monitoring photodiode 21 and compares it with the reference voltage output from the reference voltage generating circuit 13 so that the amount of light emitted from the laser diode 22 is always constant. Output the driving current. With this drive current, a DC output light for obtaining a servo signal is obtained.

In the reproducing operation of the reproducing apparatus shown in FIG.
The sampling clock pulse output from the sampling clock pulse generation circuit 11 is added to the output signal of (2). At the time when the sampling clock pulse is added, the amount of light emitted from the laser diode 22 increases. Therefore, the amount of light received by the monitoring photodiode 21 increases, and the APC circuit 12 outputs a drive current that suppresses the amount of light emitted from the laser diode 22. Therefore, when a sampling clock pulse is applied to the laser diode 22, the function of the APC circuit 12 is temporarily stopped so that the laser diode drive current is not corrected by the APC circuit 12.

The output of the APC circuit 12 is provided to the adding circuit 14. The driving current output from the APC circuit 12 and the sampling clock pulse output from the sampling clock pulse generation circuit 11 are added by the addition circuit 14. Adder circuit
The output of 14 is provided to laser diode 22 as drive current. This driving current is output as a sampling clock pulse as shown in FIGS. 2 and 3 regardless of whether the magneto-optical disk is in the pit length recording shown in FIG. 2 or the pit position recording shown in FIG. When the sampling clock pulse is not output, the current becomes a driving current for obtaining a servo signal set by the reference voltage. A laser beam for recording data reproduction corresponding to the drive current is emitted from the laser diode 22. As shown in FIGS. 2 and 3, the recording data reproducing laser light is obtained by superimposing a laser light B generated by a sampling clock pulse on a laser light A generated by a driving current output from the APC circuit 12.

The recording data reproducing laser beam emitted from the laser diode 22 is applied to the magneto-optical disk, and the reflected light is received by the reproducing photodiode 23. After the output of the reproducing photodiode 23 is amplified by the preamplifier circuit 15,
The signal is supplied to the sample and hold circuit 16 as a reproduction RF signal. The polarity of the reproduced RF signal is inverted due to the Kerr effect except for the portion where the recording pit is formed on the magneto-optical disk. Also, since the sampling clock pulse is added to the reference voltage to drive the laser diode 22, the amplitude of the reproduced RF signal at the time when the sampling clock pulse is output is more prominent than at other times. It has become.

The first delay circuit 31 delays the input sampling clock pulse in accordance with the delay amount of the reproduced RF signal by the reproducing photodiode 23 and the preamplifier circuit 15 to delay the sampled and held circuit. Output to 16. The sample and hold circuit 16 samples and holds the reproduced RF signal input at the timing of the output of the first delay circuit 31. Therefore, the sample and hold circuit 16 performs reproduction at the time when the sampling clock pulse is output.
The value of the RF signal is held (this data is used as sampling data). Sample and hold circuit 16
Is supplied to an analog / digital (A / D) conversion circuit 17.

The second delay circuit 32 delays the input sampling clock pulse corresponding to the delay amount of the sample-and-hold circuit 16 and the delay amount of the first delay circuit 31, and outputs it to the A / D conversion circuit 17. I do. The output of the second delay circuit 32 is A /
Gives the timing of A / D conversion of the D conversion circuit 17.
The conversion circuit 17 receives the output of the second delay circuit 32 and converts the sampling data output from the sample and hold circuit 16 into a digital value.

The digitized sampling data is provided to the buffer memory 18 under the control of the controller 10 and is temporarily stored. Thereafter, the sampling data is read from the buffer memory 18 and applied to the controller 10. The sampling data is encoded by the controller 10, output as encoded data, and supplied to the decoder 19. The signal is demodulated by the decoder 19 and output as demodulated data representing the recording on the magneto-optical disk.

In the reproducing apparatus described above, the magnitude of the sampling clock pulse superimposed on the drive current of the APC circuit 12 is
Even if these two currents are added and given to the laser diode as a drive current, the size must be set so that the recording pits of the magneto-optical disk will not be damaged by the reproduction laser beam emitted from the laser diode. Needless to say.

According to the present invention, the laser diode is driven by adding a pulse current of a predetermined period to the drive current of the laser diode for obtaining the servo signal when reproducing the recorded data of the magneto-optical disk. Only when the sampling clock pulse is output does the laser diode output increase. Therefore, even with a recording medium on which data is recorded at a high density by narrowing the recording pit interval, the temperature of the recording medium does not rise and the Kerr rotation angle does not decrease. Can be. Furthermore, the light emitted from the laser diode is not uniform and only increases when the pulse is output.
It is also possible to prevent damage to recording pits caused by increasing the power.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a reproducing apparatus for a magneto-optical disk,
FIGS. 2 and 3 show the relationship between the recording pits, the reproduced laser beam and the reproduced RF signal. FIG. 2 shows the pit length recording, and FIG. 3 shows the pit position recording. 11: Sampling clock pulse generation circuit, 12: APC circuit, 14: Addition circuit, 16: Sample / hold circuit, 22: Laser diode.

Claims (2)

(57) [Claims] When reproducing data recorded on a magneto-optical recording medium, a driving current of a laser diode for obtaining a servo signal is output, a pulse current of a predetermined cycle is output, and the driving current and the driving current are output. The pulsed current is added, the added drive current and the pulse current are supplied to a laser diode as a drive current for reproduction, and reflected light generated by irradiating the light emitted from the laser diode to the magneto-optical recording medium. And reproducing a data recorded on the magneto-optical recording medium by reading the data and reproducing a signal representing the data. 2. A reproduction signal representing data read from the magneto-optical recording medium is sampled in synchronization with the output of the pulse current, and the reproduced signal is recorded on the magneto-optical recording medium using the value of the reproduction signal obtained by the sampling. A reproducing method of a magneto-optical recording medium, which performs a reproducing process of existing data.