JPS58196630A - Semiconductor laser device - Google Patents

Abstract

PURPOSE:To eliminate the noises included in a laser output within a signal band of an optical disk, by providing a series resonance circuit having a resonance frequency within a signal band of the optical disk in parallel to a semiconductor laser element which is driven with a fixed level of optical output. CONSTITUTION:An LCR series resonance circuit 14 which functions as a noise filter circuit is set in parallel to a semiconductor laser 11 which is driven by a constant optical output driving circuit 13. Then the resonance frequency fO is set at the center frequency of the signal band of an optical disk. The impedance of the filter circuit 14 is sufficiently reduced with the frequency fO, and therefore both ends of the laser 11 are short-circuited. As a result, the component near the frequency fO is quickly reduced and elminated among the noise type optical output fluctuations due to the light returned from the optical disk.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a semiconductor laser driven with constant light output and used as a light source for a readout pickup of an optical disk. In particular, the present invention relates to a drive circuit that reduces noise caused by the semiconductor laser itself within the frequency range of a pit signal band recorded on an optical disk.

A conventional example of a driving circuit for a semiconductor laser used in an optical disk reading pickup is shown in FIG. The light emitted backward from the laser element 11 is received by the light receiving element 12,
Control is performed by the power supply 13 so that the first output is constant. The light emitted forward is focused on the optical disk surface 3 by the pickup optical system 2, and the reflected light is detected by the light receiving element 26.

Note that 21, 24, and 25 are lenses, a 23Fi polarizing prism 22, and a λ/4 wavelength plate.

In this system, a few percent of the light reflected from the disk surface
Nearby light may return to the semiconductor laser, and the effect of this feedback light causes noise-like optical output fluctuations in the laser light that is supposed to be in a constant output circuit. The portion of the signal spectrum component of this noise that overlaps with the frequency band of the signal recorded on the optical disk has a direct negative effect on the reading and error rate.

In a semiconductor laser, fluctuations in optical output always cause fluctuations in current due to the stimulated emission effect, so it is possible to suppress noise in optical output using an electric circuit. According to this idea, a constant light output circuit that follows the light at high speed is effective in removing noise, but in reality, such a system is prone to failure and is difficult to put into practical use. The present invention solves all miscellaneous
It is based on the idea of adding an electric circuit to the drive circuit that reduces noise within the signal frequency band rather than eliminating V.

An object of the present invention is to provide a laser drive circuit that reduces noise within the band of a signal recorded on an optical disk among noise components included in the optical output of a semiconductor laser.

Figure 2 shows the noise-reduced laser drive device (first stage) of the present invention.
(corresponding to 1 in the figure). A feature of the present invention is that an LCR series resonant circuit 14 as a noise filter circuit is inserted in parallel with the semiconductor laser element 11.

The resonant frequency f (lFi) of this resonant circuit is matched to the center frequency of the signal band of the optical disc. Filter circuit 1
The impedance of No. 4 becomes sufficiently small at the frequency f0, and both ends of the laser are short-circuited. In this case, among the noisy optical output fluctuations generated by the return light from the optical disk, the components around frequency 10 are the current fluctuations associated with the optical output fluctuations.
Although the laser light output generated from the circuit in Figure 2 contains noise components, the noise components within the signal band of the optical diode 2 are significantly reduced, so there is no reduction in the S/N ratio. However, the error rate does not worsen.

The resonance frequency fo Fi at this time is given by, and L and C are calculated from the properties of the semiconductor laser as follows (3).

. -1, eh. □11 r,: Life time of laser injected carriers τ,: Life time of photons in the resonator 111: Laser bias current Iib: Threshold current value of the laser.

The present invention can reduce miscellaneous T with such a simple electric circuit, can be easily applied to the application of semiconductor lasers to optical disks, and has great practical effects.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing a conventional semiconductor laser drive circuit for an optical disk reading pickup, and FIG. 2 is a semiconductor laser drive circuit according to the present invention aimed at reducing noise. DESCRIPTION OF SYMBOLS 1... Laser drive circuit, 2... Optical pickup optical system, optical prism, 26... Light-receiving confectionery, 31... Bit. Jin! Agent Patent Attorney Usude Rishin',""7'1"7'￥i 1 Figure 2 Figure 1

Claims (1)

[Claims] 1. In a semiconductor laser device driven with a constant first output power used for reading recording signals from an optical disk, a series resonant circuit having a resonant frequency within the signal band of the optical disk is provided in the semiconductor laser element and in parallel. Features of the semiconductor laser device.