JPH0479048A - Method for reproducing magneto-optical recording medium - Google Patents

Abstract

PURPOSE:To obtain the reflection signal of a recording medium having high intensity by adding a pulse current in a specified cycle to the driving current of a laser diode for obtaining a servo signal at the time of reproducing the recorded data on a magneto-optical disk and driving the laser diode. CONSTITUTION:At the time of reproducing the data recorded on the magneto- optical recording medium, the driving current of the laser diode 22 for obtaining the servo signal is outputted and the pulse current in the specified cycle is outputted, so that the driving current and the pulse current are added in an addition circuit 14 and the driving current and the pulse current, which are added, are given to the laser diode 22 as a driving current for reproducing. Then, reflected light generated by irradiating the magneto-optical recording medium with the light emitted from the laser diode 22 is read to obtain a reproducing signal showing the data, and the data recorded on the magneto-optical recording medium is reproduced. Thus, the intensity of the reproducing signal from the recording medium is made high.

Description

[Detailed description of the invention] Industrial applications The present invention relates to a method for reproducing a magneto-optical recording medium.

Conventional technology A method for recording data on magneto-optical recording media.

There are pit position records that have information on the presence or absence of pits and are recorded by changing the interval between pits, and pit length records that have information on the length of pits. Conventionally, regardless of the recording method, the magnetization direction of the recording medium is changed depending on the data, and the magnetic Kerr effect and Faraday effect generated by the difference in the magnetization direction are utilized. That is, a recording medium is irradiated with linearly polarized laser light of a predetermined intensity.

Reflected light whose plane of polarization has been rotated due to the magnetic Kerr effect or Faraday effect is detected by a photodetector via an analyzer. Therefore, the amount of light passing through the analyzer changes depending on the rotation angle of the polarization plane of the reflected light, and this change in the amount of light is converted into an electrical signal by a photodetector to reproduce the recorded data.

Problems to be Solved by the Invention When data is recorded at high density on a magneto-optical recording medium, the interval between recording pits becomes narrower, and the amplitude of the reproduced signal decreases. This is because the output light spot diameter of the optical head becomes a finite value due to the limitations 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 resulting reproduced signal is significantly reduced. Here, the amplitude (strength) of the reproduced signal is S.

The output light intensity of the laser diode is 1, the reflectance of the recording medium is R, the Kerr rotation angle is θ, and the MTF (Modularity) is
When α is the reduction rate of the signal due to the on-transrer function, the strength S of the reproduced signal can be expressed by the following equation.

According to the above formula, when performing high-density recording on a recording medium, it is possible to reduce the above reduction rate α by using a laser diode with a short wavelength, or by selecting an appropriate recording medium. The strength S of the reproduced signal can be increased by increasing the values of R and θ. However, if the value of I is uniformly increased in order to further increase the strength S of the reproduced signal,
Since the temperature of the recording medium increases due to the light emitted from the laser diode of the optical head, the Kerr rotation angle may decrease and recording pits may be damaged.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for reproducing a magneto-optical recording medium that can increase the intensity of a reproduced signal from the recording medium without causing damage to recording pits.

Means for Solving the Problems This invention outputs a driving current for a laser diode to obtain a servo signal and outputs a pulse current with a predetermined period when reproducing data recorded on a magneto-optical recording medium. , the above drive current and the above pulse current are added, the added drive current and the above pulse current are applied to a laser diode as drive current for reproduction, and the light emitted from the laser diode is irradiated onto the magneto-optical recording medium. The reflected light generated by this process is read and a reproduced signal representing the data is obtained.
It is characterized by performing reproduction processing of data recorded on a magneto-optical recording medium.

Also, in synchronization with the output of the pulse current, a reproduction signal representing data read from the magneto-optical disk is sampled, and the value of the reproduction signal obtained by sampling is used to reproduce the data recorded on the magneto-optical recording medium. It is preferable to do this.

According to the present invention, when reproducing data recorded on a magneto-optical recording medium, a laser diode drive current and a pulse current of a predetermined period are outputted to obtain a servo signal, and these currents are added. ing. This added current is used as a drive signal for the laser diode, and the laser
The light reflected from the magneto-optical recording medium generated by the light emitted from the diode is read to obtain a reproduction signal representing recorded data.

This reproduction signal is sampled in synchronization with the output of the pulse current, and the obtained sampling value is used to perform reproduction and reproduction processing of the recorded data, including digital signal processing such as digitization and encoding.

Embodiment FIG. 1 is a block diagram showing a reproducing apparatus for a magneto-optical recording medium 1, such as a magneto-optical disk. Figures 2 and 3 show the recording pits of the magneto-optical recording medium, the reproduction laser beam, and the reproduction RF signal; Figure 2 shows the pit length recording;
The figures each show pit position records.

The reproducing device includes a sampling clock pulse generation circuit 11 that outputs sampling clock pulses of a predetermined period. The output of this sampling clock pulse generation circuit 11 is controlled by the controller IO. The output of the sampling clock pulse generation circuit 11 is APC (＾automatic power
rControl ) circuit 12. Addition circuit 14, first
delay circuit 31 and second delay circuit 32, respectively.

The optical head 20 includes a monitor photodiode 21,
A reproduction photodiode 2 that receives reflected light from a laser diode 22 and a magneto-optical disk (path shown)
3 is included. A laser beam for reproducing recorded data is emitted by the laser diode 22 and is irradiated onto the magneto-optical disk. The reflected light of the laser beam for reproducing recorded data from the magneto-optical disk is received by the reproducing photodiode 23 and output as a reproducing RF signal. The monitoring photodiode 21 monitors the emitted laser light so that the amount of light emitted from the laser diode 22 is constant. A signal representing the amount of emitted light received by the monitor photodiode 21 is given to the APC circuit 12.

The APC circuit 12 includes a reference voltage generation circuit 13, and the reference voltage generation circuit 13 generates a reference voltage. The APC circuit 12 inputs the output signal of the monitor photodiode 21 and compares it with the reference voltage output from the reference voltage generation circuit 13, so that the output signal of the laser diode 22 is always constant. 22 drive currents are output. This drive current provides DC incident light for obtaining servo signals.

In the reproduction operation of the reproduction apparatus shown in FIG. 1, the sampling clock pulse output from the sampling clock pulse generation circuit 11 is added to the output signal of the APC circuit 12. At the time when the sampling clock pulse is added, the amount of light emitted from the laser diode 22 becomes stronger. For this reason, the monitor photodiode 21
The amount of light received by the laser diode 22 also increases, and the APC circuit 12 outputs a drive current that suppresses the amount of light emitted from the laser diode 22. Therefore, when applying the sampling clock pulse to the laser diode 22, the APC circuit 1
The function of the APC circuit 12 is temporarily stopped so that the laser diode drive current correction according to 2 is not performed.

The output of the APC circuit 12 is given to an adder circuit 14. An adder circuit 14 adds the drive current output from the APC circuit 12 and the sampling clock pulse output from the sampling clock pulse generation circuit 11. The output of adder circuit 14 is provided to laser diode 22 as a drive current. This drive current outputs sampling clock pulses as shown in Figures 2 and 3, whether the magneto-optical disk is recording the pit length as shown in Figure 2 or recording the bit position as shown in Figure 3. When the sampling clock pulse is output, it becomes a large value, and when the sampling clock pulse is not output, it becomes a drive current to obtain a servo signal set by the reference voltage. A laser beam for reproducing recorded data corresponding to this drive current is emitted from the laser diode 22. As shown in FIGS. 2 and 3, the laser beam for reproducing recorded data is sampled into the laser beam A generated by the drive current output from the APC circuit 12.
The laser beam B generated by the clock pulse is superimposed.

A laser beam for reproducing recorded data emitted from the laser diode 22 is irradiated onto the magneto-optical disk.

The reflected light is received by the reproduction photodiode 23. The output of the reproduction photodiode 23 is sent to the preamplifier circuit 1.
After being amplified in step 5, it is applied to a sample and hold circuit 16 as a reproduced RF signal. The polarity of the reproduced RF signal is reversed due to the Kerr effect in areas other than the portion where recording bits are formed on the magneto-optical disk. Also, since the laser diode 22 is driven by adding the sampling clock pulse to the reference voltage, the amplitude of the reproduced RF signal at the time the sampling clock or pulse is output is more prominent than at other times. It becomes.

Since the reproduced RF signal is delayed by the reproduction photodiode 23 and the preamplifier circuit 15, the first delay circuit 31 delays the input sampling clock pulse according to the amount of delay and outputs the input sampling clock pulse to the sample halt circuit. 16. The sample and hold circuit 16 is the first delay circuit 3
The input reproduced RF signal is sampled and held at the timing of the output of the device. Therefore, the sample and hold circuit 16 holds the value of the reproduced RF signal at the time when eight sampling clock pulses are applied (this data is used as sampling data).

The output of the sample and hold circuit 16 is given to an analog/digital (A/D) conversion circuit 17.

The second delay circuit 32 delays the input sampling clock pulse in accordance with the amount of delay in the sample and hold circuit 16 and the amount of delay in the first delay circuit 31, and outputs A.
/D conversion circuit 17. Also, the second delay circuit 32
The output of the A/D converter circuit 17 provides the timing of A/D conversion of the A/D converter circuit 17, and the A/D converter circuit 17 receives the output of the second delay circuit 32, so that the output is output from the sample-and-hold circuit 16. Convert sampled data to digital values.

Digitized sampling data.

The data is provided to buffer memory 18 and temporarily stored under the control of controller IO. The sampled data is then read from buffer memory 18 and provided to controller 10. The sampling data is encoded by the controller 10, output as encoded data, and given to the decoder 19.

The signal is then demodulated by the decoder 19 and output as demodulated data representing the recording on the magneto-optical disk.

In the above-mentioned reproducing device, the magnitude of the sampling clock pulse superimposed on the drive current of the APC circuit 12 is such that even if these two types of pulses are added together and given to the drive current to the laser diode, Needless to say, the size is set so that the recording pits of the magneto-optical disk will not be damaged by the emitted reproduction laser beam.

Effects of the Invention According to the present invention, when reproducing data recorded on a magneto-optical disk, the laser diode is driven by adding a pulse current of a predetermined period to the drive current of the laser diode for obtaining a servo signal. The laser diode output increases only when a sampling clock pulse is output. Therefore, even if data is recorded at high density by narrowing the recording pit interval, the temperature of the recording medium will not rise and the Kerr rotation angle will not decrease, making it possible to obtain a reflection signal of a recording medium with high intensity. I can do it. Furthermore, since the light emitted from the laser diode is not uniformly large but becomes large only when a pulse is output, it is also possible to prevent damage to the recording pits caused by increasing the laser power.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a magneto-optical disk reproducing device.
FIGS. 2 and 3 show the relationship between recording pits, reproduction laser beams, and reproduction RF signals, with FIG. 2 showing pit length recording and FIG. 3 showing pit position recording, respectively. 11...Sampling clock pulse generation circuit. 12...APC circuit. 14...Addition circuit. 1B...Sample/hold circuit. 22...Laser diode. that's all

Claims (2)

[Claims] (1) When reproducing data recorded on a magneto-optical recording medium, output a drive current for a laser diode to obtain a servo signal, output a pulse current with a predetermined period, and output the drive current and the pulse current at a predetermined period. The added drive current and pulse current are applied to a laser diode as a drive current for reproduction, and the reflected light generated by irradiating the output light of the laser diode to the magneto-optical recording medium is read. 1. A method for reproducing a magneto-optical recording medium, comprising: obtaining a reproduction signal representing data, and performing reproduction processing of data recorded on the magneto-optical recording medium. (2) Data recorded on the magneto-optical recording medium by sampling a reproduction signal representing data read from the magneto-optical recording medium in synchronization with the output of the pulse current, and using the value of the reproduction signal obtained by sampling. 1. A method for reproducing a magneto-optical recording medium, comprising performing a reproducing process.