JPS62119743A - Semiconductor laser driving device - Google Patents

Abstract

PURPOSE:To reduce laser noises produced at the time of recording, reproducing, and erasing, by ceasing high-frequency drive under the recording and erasing modes. CONSTITUTION:A semiconductor laser 1 is driven by a driving circuit 2. A laser chip 3 and photodetector 4 for monitor are provided in the semiconductor laser 1 and the laser chip 3 is connected with a driving line 31. The photodetector 4 is connected with a detecting line 41. The driving circuit 2 is composed of a driver amplifier 21 which normally drives the laser chip 3 and high-frequency oscillator circuit 22 and the output line of the driver amplifier 21 and output line of the oscillator circuit 22 are directly coupled with each other through a capacitor C and become the driving line 31. Upon receiving pulses from a host controller 5 at the time of recording and erasing, the driver amplifier 21 makes pulse oscillation in accordance with the pulses.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a semiconductor laser driving device using a high-frequency oscillator that reduces laser noise of a semiconductor laser, and in particular, during pulse oscillation of a semiconductor laser 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. In recent years, with the development of transverse mode control technology for semiconductor lasers, an increasing number of semiconductor lasers are oscillating in a fundamental transverse mode and in a uniform longitudinal mode. However, this improves coherence, and conversely, when it is incorporated into a device, feedback noise occurs when the light emitted from the semiconductor laser is reflected from the end face of the optical component or the disk surface and returns to the laser. A problem has arisen. This noise is caused by the interference of highly coherent light between the emitted light and the reflected light, causing the laser's longitudinal oscillation mode to jump or oscillate in multiple longitudinal modes, making it unstable. . Instability of the oscillation longitudinal mode is also induced by temperature changes. In other words, the temperature changes due to temperature changes. Noise is generated during this mode jump, and these noises are used in optical communications and optical discs.
This causes deterioration of signal S/N.

As a method to reduce these noises,
As described in No. 6, it has been proposed to provide a high frequency oscillator in the laser drive circuit to modulate the laser at high frequency.

However, the purpose of this method was only to reduce laser noise in the case of DC drive in which continuous high-frequency modulation is performed.

[Purpose of the invention]

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

[Summary of the invention]

The basic concept of the present invention is to perform high-frequency driving only during reproduction, and to suspend high-frequency driving during recording mode and erasing mode. Semiconductor lasers record and erase at the maximum rated output, and if 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.
In the present invention, a high frequency oscillator is activated during recording mode and erasing mode.

[Embodiments of the 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, and the light emitted from the semiconductor laser 1 is focused by the coupling lens 7,
Beams brick 8. Galvano mirror 9
, and is narrowed down to a spot of about 1 μm on the disk 11 on which the magneto-optical recording film is formed. The magneto-optical recording film is an amorphous compound of a transition metal and a rare earth metal, such as Tb-Fe.

When irradiated with an output laser beam, heat is generated and the temperature rises, and when it reaches the cue temperature, magnetization disappears. At this time, when a magnetic field is applied by the electromagnetic coil 12 as an external magnetic field, only the part where the temperature has increased will be magnetized in that direction, and when the linearly polarized light incident on the film is reflected in the direction opposite to the surrounding magnetization direction, the angle of rotation will change. Utilizing different Kerr effects.

When the angle of optical rotation is θ, for example, + with respect to the upward direction of magnetization.
If it is θ, then it becomes 10 for the downward direction. This angle of optical rotation is called the Kerr rotation angle, and although it varies depending on the composition of the recording film and the structure of the disk, it is very small, about 0.35 degrees. The Kerr rotation angle that is this signal component is disk 1
It is included in the light reflected from the focusing lens 10. After passing through the gal parts mirror 9 and being separated by the beam splitter 8, the light passes through the lens 13 and is separated by the beam splitter 14 into a servo system and a signal detection system. The servo system is composed of a lens 15 and a photodetector 16, and the AF system, which is well known in the past, uses an astigmatism method, and the TR system uses a diffraction differential method to position a light spot on the disk (the drive circuit is not shown). do not). The signal detection system uses a differential system in which the light intensity is divided into two equal parts using a λ/2 plate 17 (λ is the wavelength of the semiconductor laser) and a polarizing beam splitter 18, and the outputs of the photodetectors 19 and 20 are differentiated using a differential amplifier 23. A magneto-optical signal is obtained. This method has the effect of reducing noise caused by fluctuations in light intensity, such as laser noise and disk noise.

The sum of the outputs of the two photodetectors 19 and 20 is added to the adder 24.
This is obtained by detecting the amount of light reflected from the disc, so it is input in advance in the form of concavities and convexities on the disc.

The configuration and operation of the controller 5 will be explained using FIG. 2. The magneto-optical signal obtained from the differential amplifier 23 and the address information signal obtained from the adder 24 are switched by the analog switch 51 using the timing from the mark detection circuit 52 which inputs the 1st address information signal, and is converted into an information signal with address information. becomes.

This information signal is digitized by a pulse generator 53, and converted into a VF○ (Variable Frequency) signal which generates a timing clock for reading in a demodulator circuit 55.
Information data and address data are read based on the clock from the yOscillator circuit 54 and input to the microprocessor 56 for recognition. Next, the information data and address data sent from the microprocessor 56 are synchronized in timing by a modulation circuit 57.

The signal is modulated (for example, 2-7 modulation) and input to the automatic power control circuit 6. The sequence circuit 58, which controls the sequence of the device, generates recording, playback, and erase mode signals according to commands from the microprocessor 56, and the automatic power control circuit 6, which generates a laser drive signal and performs automatic power control. The automatic power control circuit 6 inputs the laser drive signal (D
Automatic power control is performed in response to a control signal from a monitoring photodetector of the semiconductor laser 1.

Next, high frequency driving of the semiconductor laser will be explained with reference to FIG. The semiconductor laser 1 is driven by a drive circuit 2. Laser chip 3 inside semiconductor laser 1 Monitoring photodetector 4
The laser chip 3 is connected to the drive line 31,
The monitoring photodetector 4 is connected to the detection line 41. The drive circuit 2 consists 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 receives pulses from the host controller 5 during recording and erasing.

Pulse oscillation is performed accordingly. The recording mode, reproduction mode, and erasing mode of the magneto-optical disk will be explained using FIGS. 4 and 5. Figure 4 shows the waveforms in each mode, (A) is the playback mode and the mode signal a
remains “L″’, the information data signal remains “L”,
The driver amplifier output C is In (mA), the high frequency oscillation circuit output d remains ON, and the laser drive current waveform e is the sum of the driver amplifier output C and the high frequency oscillation circuit output d. (B) is the recording mode in which high-frequency weighting is performed, and the mode signal a becomes "H" for each sector to perform sector-by-sector recording, the information data signal is a sector period data pulse, and the driver output C is a waveform in which the information data It is added to the two currents IR during reproduction, and the high frequency oscillator output d is the mode signal af (O
N), the mode signal a becomes a waveform that oscillates only when it is II L '1, and the laser drive waveform e becomes the sum of the driver output C and the high-frequency oscillator output d, and the high-frequency weight is generated only when reading the header signal between sectors. will be done. (C) is the erase mode, and compared to the recording mode of (B), the information data b has no data pulse and is only "HII" in the sector, and the other operations are the same.

Figure 5 shows the laser driving state in each mode, and the fourth
This is a reference diagram of the figure. Further, FIG. 6 shows a basic example of the high frequency oscillation circuit 22. Detection line 4 from monitor photodetector 4
1 is led to an automatic power control circuit 6 for laser power, and controls a driver amplifier 21 using the detected control signal,
Perform power control.

The present invention has been applied to the Hitachi semiconductor laser HL-8314E type (83
The reconfirmed results using a high-frequency device (0nm, 30mW output) show that the relative noise level RIN value can be reduced by about two orders of magnitude during recording, and that errors do not occur in the recorded data even if the high-frequency weight is stopped during recording and erasing. Ta. At this time, the high frequency oscillation frequency was 600 MHz, and the current modulation degree was 140 to 160%.

〔Effect of the invention〕

As described above, according to the present invention, recording is performed by controlling the high frequency weight during recording, reproduction, and erasing.

This has the effect of reducing laser noise during reproduction and erasing.

[Brief explanation of drawings]

1 to 6 are diagrams for explaining the present invention in detail. 1...Semiconductor laser, 2...Drive circuit, 3...Laser chip, 4...Photodetector for monitoring, 5...Controller, $1 Figure 1j Tomi 2 Figure ¥j 3 Kuchi Tomi 5 Figure 104 Figure 5 Power

Claims (1)

[Claims] 1. In a semiconductor laser driving device that uses a semiconductor laser and a high-frequency oscillator to reduce laser noise emitted by the semiconductor laser by driving the semiconductor laser with the high-frequency oscillator, the recording or erasing of information is provided. A semiconductor laser driving device characterized in that driving of the high frequency oscillator is stopped when driving the semiconductor laser with high output pulses. 2. A semiconductor laser driving device according to claim 1, wherein the high frequency driving circuit is controlled using a mode signal representing recording and erasing.