JP2528821B2 - Optical information processing device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser driving device using a high-frequency oscillator for reducing laser noise of a semiconductor laser, and particularly to a semiconductor laser pulse oscillation such as recording or erasing. The present invention relates to a semiconductor laser drive device.

[Background of the Invention]

Semiconductor lasers are often used as light sources for optical information processing devices such as optical disks and optical printers. recent years,
Lateral mode control technology for semiconductor lasers has been developed, and many of them have a fundamental lateral mode oscillation and a uniform longitudinal mode oscillation. However, this improves the coherence, and conversely, when it is incorporated into the device, when the light emitted from the semiconductor laser is reflected from the end surface of the optical component or the disk surface and returns to the laser again, it is called feedback noise. The problem of occurring has arisen. This noise is due to the fact that the light with good coherence interferes with the emitted light and the reflected light, and the oscillation longitudinal mode of the laser becomes unstable due to jumping or multiple longitudinal mode oscillation. . Instability of the oscillation longitudinal mode is also induced by temperature change. That is, the wavelength of the single longitudinal mode oscillation shifts due to a temperature change, and not only continuously shifts, but also discretely jumps and shifts. Noise occurs during this mode jump. These noises are signal S / N in optical communication and optical disk.
Cause deterioration.

As a method for reducing these noises, as disclosed in Japanese Examined Patent Publication No. 59-9086, it is considered that a laser driving circuit is provided with a high-frequency oscillator and the laser is subjected to high-frequency modulation. However, this method was only intended to reduce the laser noise in the case of DC drive in which continuous high frequency modulation is performed.

[Object of the Invention]

It is an object of the present invention to provide a laser driving device which is effective not only when reproducing information but also when recording and erasing information.

[Outline of Invention]

The basic idea of the present invention is to drive at high frequency only during playback,
High-frequency driving is stopped in the recording mode and the erasing mode. The semiconductor laser performs recording / erasing at the rated maximum output, and if the high-frequency weight is applied in this state, the rated output will be exceeded, and the life of the laser itself will be adversely affected. Sometimes the high frequency drive is stopped.

Example of Invention

An embodiment of the present invention will be described below with reference to FIG. This is a case where it is applied to a magneto-optical disk device, in which the light emitted from the semiconductor laser 1 is condensed by a coupling lens 7 and collimated into a beam split 8 and a galvano mirror.
9, After passing through the aperture lens 10, the aperture is focused as a spot of about 1 μm on the disk 11 on which the magneto-optical recording film is formed. As the magneto-optical recording film, there are amorphous compounds of transition metals and rare earth metals, such as Tb-Fe and Tb-Fe-Co, which form a perpendicular magnetic film in which the magnetization is oriented in the direction perpendicular to the plane. When this film is irradiated with high-power laser light, heat is generated and the temperature rises, and when the temperature reaches the Curie temperature, the magnetization disappears. At this time, when a magnetic field is applied as an external magnetic field by the electromagnetic coil 12, only the temperature-increased portion is magnetized in that direction, and information recording is executed when the magnetization direction is opposite to the surrounding magnetization direction. Information is erased. The signal reproduction utilizes the Kerr effect in which the angle of optical rotation is different when the linearly polarized light incident on the film is reflected depending on the direction of magnetization. When the optical rotation angle is θ _K , for example, if it is + θ _K for upward magnetization, −θ _K for downward magnetization.
Becomes This optical rotation angle is called the Kerr rotation angle, and although it differs depending on the composition of the recording film and the disk structure, it has a very small point of about 0.35 degrees. The Kerr rotation angle that is this signal component is included in the light reflected from the disk 11, and the focusing lens 10,
After passing through the galvanometer mirror 9, the beam splitter 8 separates the optical path, and then passes through the lens 13 and the beam splitter 14 separates the optical system into a servo system and a signal detection system. Servo system is a lens
It is composed of 15 and photodetector 16. The AF system, which is well known in the past, uses the astigmatism method, and the TR system uses the diffraction differential method to position the optical spot on the disk (the drive circuit is not shown). The signal detection system is a λ / 2 plate 17 (λ is a semiconductor laser wavelength), a polarization beam splitter 18 divides the light amount into two equal parts, and the output of the photodetectors 19 and 20 is differentially differentiated by a differential amplifier 23. Then, a magneto-optical signal is obtained. This method has an effect of reducing noise such as laser noise and disk noise caused by fluctuations in light amount. The sum of the outputs of the two photodetectors 19 and 20 is obtained by an adder 24, which detects the reflected light amount of the disk, and is used for detecting the address information or the like which is recorded beforehand in the form of unevenness on the disk. . The detected magneto-optical signal and address information signal are input to the controller 5.

The configuration and operation of the controller 5 will be described with reference to FIG. The magneto-optical signal obtained from the differential amplifier 23 and the address information signal obtained from the adder 24 are analog switches 51.
In the above, the address signal is switched by using the timing from the mark detection circuit 52 to which the address information signal is input, and the information signal with the address information is obtained. This information signal is digitized by the pulse conversion circuit 53, and a VFO (Variable Frequency Oscillator) circuit for generating a read timing clock in the demodulation circuit 55.
The information data and address data are read based on the clock from 54 and input to the microprocessor 56 for recognition.
Next, the information data and the address data sent from the microprocessor 56 are modulated (for example, 2-7 modulated) after the timing is adjusted by the modulation circuit 57, and the automatic power control circuit 6
Is input to A sequence circuit 58, which controls the sequence of the apparatus, generates a mode signal for recording, reproducing, and erasing in response to a command from the microprocessor 56, generates an automatic power control circuit 6 for performing laser drive signal generation and automatic power control, and a laser It is input to the high-frequency transmission circuit 22 provided in the drive circuit 2. The automatic power control circuit 6 sends a laser drive signal (DC + pulse drive) to the drive circuit 2 and receives a control signal from the monitoring photodetector of the semiconductor laser 1 to perform automatic power control.

Next, high frequency driving of the semiconductor laser will be described with reference to FIG. The semiconductor laser 1 is driven by the drive circuit 2.
Laser chip 3 in semiconductor laser 1 and photo detector 4 for monitoring
The laser chip 3 is connected to the drive line 31, and the monitoring photodetector 4 is connected to the detection line 41. The drive circuit 2 is composed of a driver amplifier 21 that normally drives the laser chip 3 and a high frequency oscillation circuit 22, and the output line of the driver amplifier 21 and the output line of the high frequency oscillation circuit 22 are directly connected through a capacitor C to form a drive line 31. The driver amplifier 21 outputs a pulse from the host controller 5 during recording and erasing, and oscillates the pulse in response to the pulse. Figure 4,
A recording mode, a reproducing mode and an erasing mode in the magneto-optical disk will be described with reference to FIG. FIG. 4 shows the waveform in each mode. (A) remains in is the mode signal a "L" playback mode, while the information data signals b is "L", the driver amplifier output C is I _R (mA), high-frequency oscillator output d remains turned ON, The laser drive current wavelength e is the sum of the driver amplifier output C and the high frequency oscillation circuit output d, and the high frequency weight is continuously performed. (B) is a recording mode, the mode signal a becomes "H" for each sector for recording in sector units, the information data signal b generates a data pulse in the sector period, and the driver output C shows the current during reproduction. The wavelength becomes the weight of I _R by the information data I _W , and the high frequency oscillator output d outputs the mode signal a (O for each sector.
N) makes the wavelength oscillate only when the mode signal a is “L”, and the laser drive wavelength e is the sum of the driver output C and the high frequency oscillator output d. It will be heavy.
(C) is an erasing mode, the information data b has no data pulse and is "H" in the sector as compared with the recording mode of (B), and other operations are the same.

FIG. 5 shows a laser driving state in each mode and is a reference diagram of FIG. FIG. 6 shows a basic example of the high frequency oscillation circuit 22. Detection line 41 from the photodetector 4 for monitor
Is guided to the automatic power control circuit 6 for laser power, and controls the driver amplifier 21 using the detected control signal to perform power control.

The present invention is based on the Hitachi semiconductor laser HL-8314E (830nm, 30mW
As a result of confirmation using the output), it was found that the relative noise level RIN value could be reduced by about two digits during reproduction, and that no error occurred in the recorded data even when the high frequency weight was stopped during recording and erasing. At this time, the high frequency oscillation frequency was 60 MHz and the current modulation degree was 140 to 160%.

〔The invention's effect〕

As described above, according to the present invention, by controlling the high frequency weight at the time of recording, reproducing and erasing, there is an effect that the laser noise at the time of recording, reproducing and erasing can be reduced.

[Brief description of drawings]

1 to 6 are views for explaining an embodiment of the present invention. 1 ... Semiconductor laser, 2 ... Drive circuit, 3 ... Laser chip, 4 ... Monitor photodetector, 5 ... Controller,
6 ... Automatic power control circuit, 22 ... High frequency oscillation circuit.

Claims (2)

(57) [Claims] 1. A semiconductor laser, driving means for driving the semiconductor laser, control means for controlling the driving means, an optical system for guiding the emitted light of the semiconductor laser onto a recording medium, and returning from the recording medium. In an optical information processing apparatus which has a light detecting means for detecting light and a signal reproducing system for forming a signal based on the output of the light detecting means, and which optically records and reproduces information, the driving means comprises: The control means has a modulation means for modulating the semiconductor laser and a high-frequency oscillation means connected between the modulation means and the semiconductor laser via a capacitor, and the control means controls a state of recording, erasing or reproducing of information. When the mode signal forming means for obtaining the indicated mode signal is provided and the mode signal indicates recording or erasing of information, the application of the high frequency current to the semiconductor laser by the high frequency oscillating means is stopped. Optical information processing apparatus, characterized in that. 2. The optical information processing apparatus according to claim 1, wherein the mode signal forming means is a sequence circuit for generating a mode signal indicating each of recording, reproducing and erasing states of information. .