JPS63236388A - Semiconductor laser device - Google Patents

Abstract

PURPOSE:To prevent noises almost completely from generating even it a mode hopping occurs by a method wherein a current inlet is rendered narrower than a current trapped in lateral mode by refractive index. CONSTITUTION:A current, which is injected into a active layer 4 through a V groove provided on a mesa 10, is trapped by use of an GaAs current block layer 2 on a substrate 1 side. An electrode 8 is formed on a n-GaAs layer 6 through the intermediary of a SiO2 film 7 and kept only in contact with the layer 6 at the point above the V groove, wherefore a current is effectively constricted. Namely, a current injection is performed more narrowly than a current trapped by refractive index. Thereby, an oscillator mode spectrum oscillates in plural modes. And, when a laser with a refractive wave guide structure is operated in a gain wave guide manner by concentrating a current, a saturable absorber is horizontally formed in the junction of a active layer, which effect causes a light output to vary by a few GHz in frequency. By this effect, each mode gets broader in spectrum width. Even it a temperature of a semiconductor laser changes, a stable noise property could 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 utilizes a light emission phenomenon caused by band-to-band transition of a GaAs semiconductor, and forms a resonator using a crystal plane. 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 into 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 refractive index.

Since the waveguide mechanism of the active transverse mode approaches gain waveguide from refractive index waveguide, higher-order modes intervene in the transverse mode, which causes oscillation in multiple resonator modes. Then,
Even if mode hopping occurs, the laser oscillation wavelength is equivalent to continuously changing as a whole, and almost no noise is generated.Embodiment FIG. 1 shows a semiconductor laser device according to an embodiment of the present invention. A structural diagram is shown. To confine the current injected into the active layer 4, an n-GaAs current blocking layer 2 is used on the substrate 1 side, and the current is injected through a V-groove 12 formed on the mesa 1o. Further, an electrode 8 is formed on the n-GaAs layer 6 by a SiO2 film 7.
However, only the position above the groove is in contact with layer 6,
It is designed to increase the effect of current constriction. That is, the current injection width is narrower than the 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 horizontally 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 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, it is possible to realize a semiconductor laser device that does not generate any noise due to mode hopping, which has significant 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-GALA! ! Board, 2...
・n-Gamus current blocking layer, 3...P
-GaAlAs cladding layer, 4...GaAJA
s active layer, 6...n-GaAlAs cladding layer, 6...n-GILA5! contact layer,
7...5102 film, 8...MuGeH
i electrode, 9... mu Zn electrode, 1o...
・Mesa, 11...Ridge, 12...V
Mizo 0 Name of agent Patent attorney Toshio Nakao and 1 other person/-
P-wide tAs base plate 2. J ---7'L-(拉AS scrap, 3-r-cra, Al25s71t 4.-trade'7-ttAlAs layer S ---7t -Crct-AIAs layer'7--Si
θ? Membrane 8- LLcreNi'fL") Fixq---hat
Lzn end k 10- Mesa 2nd drawing length (false) 3rd figure 0 20 4o 6゜1 and (
°0)

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, a P-n heterojunction is formed on the semiconductor layer, an insulating film having an opening at a position corresponding to the V-shaped groove is formed on the top layer, and an electrode metal is formed on the uppermost layer. A semiconductor laser device, wherein the semiconductor laser device is in contact with the uppermost layer through the opening.