JPS63236389A - Semiconductor laser device - Google Patents

Abstract

PURPOSE:To prevent noises almost from generating even if a mode hopping occurs by a method wherein a current injection width is made narrower than a confinement width of a lateral mode due to a refractive index. CONSTITUTION:A current, which is injected into an active layer through a V groove 12 provided on a mesa 10, is confined by use of a n-GaAs current block layer 2 on a substrate 1 side. Zn is diffused into a part of an n-GaAs layer 6 other than a part corresponding to the V groove for the formation of a p-type structure and the part not diffused with Zn is only kept in ohmic contact with an electrode 8 to make a current constriction effective. thereby, an oscillator mode spectrum oscillates in plural modes. And when a laser with a refractive index wave guide structure is operated in a gain wave guide manner by controlling a current, a saturable absorber is formed in junction of the active layer, which effect causes a light output to vary by a few GHz in frequency and also render a spectrum wider in each mode. Furthermore, a stable noise property can be obtained without any excess noises.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a semiconductor laser device used in optical information processing equipment.

2. Description of the Related Art Semiconductor laser devices are small and highly efficient, and are therefore widely used as laser light sources in the field of optical information processing. Particularly in the field of optical discs, which have been significantly developed in recent years, miniaturization of optical pickups for recording and reproducing information is impossible without semiconductor lasers.

Now, a semiconductor laser takes advantage of the light emission phenomenon caused by band-to-band transition in a GaAs semiconductor, and uses crystal planes to form the entire cavity. The spectrum of emission due to interband transitions is wide;
Laser oscillation occurs in the resonator mode at its peak wavelength. The peak wavelength corresponds to the energy gap difference between bands, so if the energy gap changes due to a change in the injection current or a change in the temperature of the crystal, the peak wavelength changes and the laser oscillation wavelength shifts to a different resonator mode. This is called mode hopping. When a semiconductor laser is used in an optical disk device, the laser beam is focused on the disk and its own laser beam returns to the semiconductor laser in order to read information based on the strength of the reflected light (playback signal) from the disk. .

This phenomenon also changes the peak emission wavelength and causes mode hopping. Accompanying this mode hopping phenomenon, the laser oscillation wavelength changes discretely, and the laser light output changes during hopping.

Problems to be Solved by the Invention When the laser light output changes due to mode hopping,
Noise will be mixed into the reproduced signal, causing an error in reading information. Therefore, when using a semiconductor laser to reproduce an optical disk, it is necessary to use a semiconductor laser device in which the fluctuation (noise) of the laser light due to mode hopping is as small as possible. However, since a normal semiconductor laser oscillates in one resonator mode, it generates extremely large noise during mode hopping.

Means for Solving the Problems The semiconductor laser device of the present invention is constructed such that the current injection width is narrower than the transverse mode confinement width due to the total refractive index.

Since the waveguide mechanism of the active transverse mode approaches gain waveguide from refractive index waveguide, a higher-order mode intervenes in the transverse mode, which causes oscillation in a plurality of resonator modes. Then,
Even if mode hopping occurs, the laser oscillation wavelength changes continuously as a whole, and almost no noise occurs.

Embodiment FIG. 1 shows a structural diagram of a semiconductor laser device according to an embodiment of the present invention. In order to confine the current injected into the active layer 4, an n-Ga-S current blocking layer 2 is used on the substrate 1 side, and the current is injected from the 2V groove 12 formed on the mesa 1Q. In addition, in the n-GaAs layer 6, there are
The Zn f is diffused to make it P-type, and ohmic contact can be made with the electrode 8 only in the non-diffused portion to increase the effect of current confinement. That is, the current injection width is narrower than the transverse mode confinement width due to the refractive index.

FIG. 2 shows the resonator mode spectrum. It can be seen that the spectrum oscillates in multiple modes. In addition, when a laser with a refractive index waveguide structure is used as a gain waveguide by narrowing down the current, a saturable absorber is formed in the horizontal direction at the junction of the active layer, and this action increases the optical output at a frequency of several GH2. It sways. This effect widens the spectral width of one mode.

FIG. 3 shows the relative noise intensity (RIM) of the laser beam when the temperature of the semiconductor laser is completely changed.

It can be seen that stable noise characteristics with no excess noise generated are obtained.

Effects of the Invention According to the present invention, a semiconductor laser device that does not generate any noise due to mode hopping can be realized, and has great effects when applied to optical discs and the like.

[Brief explanation of drawings]

FIG. 1 is a structural diagram of a semiconductor laser device of the present invention, FIG. 2 is a diagram showing a spectrum, and FIG. 3 is a diagram showing noise characteristics. 1...P-GaAs substrate, 2...n
-Ga S electric current -172 layer 3...P -Ga
1AS cladding layer, 4...GaA/JAs active layer, 5...n-Ga 5-layer 1ks rad layer, 6
......n-(ram S contact layer, 7...
...Znn diffusion type inversion region (hatched area), 8...
MuuGeNi electrode, 9...Human uZn electrode, 10
...Mesa, 11...Ridge, 12...
...V groove. Name of agent: Patent attorney Toshio Nakao and 1 other person/
---P -Cra, AS board? , 1-71. - cra, AS scrap 3-F-Qa, AlAs fake 4--- cra-AIA s layer a --- Au-cretvi 琶pole q---Ha LLz Kuran pole/Z-V groove 2nd figure λAn - Jhi (Ri 1ri 7t) Fig. 3 Oπ 406θ: 2L degrees ('C)

Claims (1)

[Claims] A semiconductor layer of a conductivity type opposite to the one conductivity type is provided on a semiconductor substrate of one conductivity type having a convex mesa, and a groove is formed in the semiconductor layer at a position directly above the mesa. , there are ridges on both sides thereof, a P-n heterojunction is provided on the semiconductor layer, and the top layer has the opposite conductivity type at a position corresponding to the groove, and the other part has the one conductivity type. A semiconductor laser device characterized by: