JPS5987888A - Semiconductor laser element - Google Patents

Abstract

PURPOSE:To prevent any noise from increasing and to improve the combination of semiconductor laser element of a gain waveguide mechanism with an optical system by a method wherein the thickness of active layer of a crystal layer for operating laser deposited on an internal stripe for current strangulation the width of which becomes wider near an end of a resonator and narrower inside the resonator. CONSTITUTION:A current confining layer 2 is grown in a GaAs substrate 1 to form a stripe groove by one time photoetching process. Next when a P type clad layer 23 is epitaxially grown, the surface of the layer 3 is flattened in the region with stripe width of W2 while the same surface is dented in the region with stripe width of W1 because more P-GaAlAs is needed to bury the stripe groove in the region with wider stripe width of W1. In such a constitution, the refractive index difference in the lateral direction is larger to focus a laser beam on a spot with fine diameter not exceeding 1mum near an end of a resonator while the laser beam is enlarged up to 3-4mum in the lateral direction due to smaller refractive index difference in the same direction inside the resonator.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a semiconductor laser device that reduces interference noise due to returned light.

<Prior Art> Conventionally, when a semiconductor laser device is used as a light source for a disk information processing device, it is used in a video disk.

When coupled to an optical system such as an audio disc, the return light of the output laser light due to reflection from the disc surface may be re-injected into the semiconductor laser element, and the solid line in Figure 7 may occur due to interference of the re-incoming light with the output light. As shown in Figure 1, the linearity between the injected current and the optical output decreases, and as shown in the solid line No. 1 in Figure 1, the noise of the output light increases, so that it may become impossible to put it into practical use. As a means to solve this problem, the current injection width, that is, the stripe width, has been changed from the usual 70~/j
Attempts have been made to narrow the carrier diffusion length in the active layer to about 2 to 1.mu.m compared to .mu.m in order to avoid the occurrence of distortion or an increase in return optical noise. In such a semiconductor laser, the light distribution of the laser is determined by the gain distribution, but since the cavity volume is small, the involvement of the spontaneous emission laser mode becomes large, and the injection current density is large, so the gain spectral width is is expanded, oscillates in a multi-axis mode, and the influence of re-incident light is reduced by this multi-axis mode oscillation.

However, the gain guided i! The semiconductor laser element of the structure is
Since the near-field image changes due to the injection current or changes over time, the coupling with the optical system becomes unstable and the astigmatism is large, resulting in a disadvantage that the coupling efficiency with the optical system such as a lens decreases.

<Purpose of the Invention> The FUJIJ fundamentally solves the above-mentioned drawbacks of conventional semiconductor laser devices, and has a refractive index waveguide mechanism and longitudinal multi-mode oscillation, which reduces the increase in noise. It is an object of the present invention to provide a new semiconductor laser device for nails, which can prevent the above problems and improve the coupling state between the semiconductor laser device of the gain waveguide mechanism and the optical system.

<Embodiment> FIG. 3 is a cross-sectional configuration diagram in the resonator length direction of a semiconductor laser device showing an embodiment of the present invention.

n- to control the current path on/on the P-GaAs substrate
Current confinement layer made of GaAs, 2.1)-GaAI
P-type cladding layer made of As3. p or n-GaAIA
The active layer consists of S (or GaAs).

An n-type rad layer made of n-GaAIAS! , n
- A cap layer B made of GaAs is sequentially laminated by liquid phase epitaxial growth. Note that 7 and ♂ in the figure are respective end faces of the resonator. The thickness of the current confinement layer is O
After being deposited on a GaAs substrate 1, striped grooves are etched from the surface to a depth of about 1 μm from the surface to the GaAs substrate/substrate layer to form a current path.

GaAs substrate/substrate method, P-side electrode made of u-Zn, cap layer Z with Au-Ge-Ni-
An n-side electrode made of Au is formed by vapor deposition. Since the region where the current confinement layer is interposed is connected with opposite polarity, no current flows, and only the striped groove portion from which the current confinement layer has been removed serves as a current path.

-Bl is a plane view showing the cross-sectional structure inside the resonator.

Inside the resonator, the width Wl of the stripe groove formed in the current confinement layer J is 2 μm, and the length of the stripe groove having the width WI is 20 μm. Under the influence of the stripe grooves, the active layer on the end face of the resonator assumes a plano-convex shape or a crescent shape directly above the stripe grooves. On the other hand, inside the resonator, the width W2 of the stripe groove formed in the current confinement layer is μ
m, and the length is set to θθμm. Note that the center line of the stripe groove matches the end face of the resonator internally. The active layer in this portion is flattened and is not affected by the shape of the stripe groove.

FIG. 2 is a perspective view showing the shape of a GaAs substrate/substrate method confinement layer grown and striped grooves formed by seven photo-etching steps.

When the P-type cladding layer 3 is epitaxially grown in the state shown in the figure, the upper surface of the P-type cladding layer 3 becomes flat in the stripe width W2 region, and a depression is formed in the upper surface in the stripe width W1 region.

This is because the groove width is wider in the stripe width W1 region, and therefore more P-GaAIAs is required to fill this groove portion. Therefore, the active layer grown on this P-type cladding layer 3 becomes as shown in FIGS. 7 and 5 depending on the top surface shape of the P-type cladding layer 3. With such a structure, although the resonator ends, the difference in refractive index in the lateral direction becomes small inside the resonator, so that light spreads by 3 to 1 μm in the lateral direction.

In this device, a P-type cladding layer 3. For example, the respective mixed crystal ratios x r Y , z of the active layer (g) and the n-type cladding layer (j) are as follows: The cladding layer 3 is made asymmetrical as shown in FIG. This makes it difficult for light to leak to the substrate side, so that the difference in refractive index in the lateral direction becomes sufficiently small, and the laser is guided by the gain like a normal electrode stripe laser, resulting in longitudinal multimode oscillation. However, the resonator end face is
Since the thickness of the active layer changes in the lateral direction, the wave is guided by the refractive index, so that the beam waste end faces coincide and no astigmatism appears.

FIG. 7 is a characteristic diagram showing the current-light output characteristics of the semiconductor laser device shown in FIG. 3. FIG. 2 is a spectrum diagram of the semiconductor laser confectionery shown in FIG. 3.

The semiconductor laser shown in FIG. 3 has a DC output / j m W
It oscillates in longitudinal multimode up to
It was below.

<Effects of the Invention> As detailed above, according to the present invention, longitudinal multi-mode oscillation is achieved, and injection current vs. light output characteristics with good linearity and less influence by return light from the laser end face/\ can be obtained. Moreover, it is possible to obtain stable output light with small astigmatism, high coupling efficiency with the optical system, and a near-field image that does not change due to injection current, changes over time, etc.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the injection current versus light output characteristic of a conventional semiconductor laser device. The solid line is the characteristic curve when there is 14 human incident light, and the broken line is the characteristic curve when there is no re-incident light. Figure 2 shows a conventional semiconductor laser device! It is a 1f sound characteristic diagram. Curve 1□ is a characteristic curve when there is re-incident light, and curve No. 2 is a characteristic curve when there is no re-incident light. FIG. 3 is a cross-sectional view of the structure of a semiconductor laser device showing an embodiment of the present invention. The second figure is a sectional view taken along the line A-A in FIG. FIG. 5 is a sectional view taken along line BB in FIG. 3. FIG. 2 is a detailed perspective view of essential parts showing the substrate structure of the semiconductor laser device shown in FIG. 3. FIG. FIG. 7 is a characteristic diagram showing the current versus optical output characteristics of the semiconductor laser device shown in FIG. 3. FIG. 2 is a spectrum diagram of the semiconductor laser device shown in FIG. 3. K...GaAs substrate, C...Current confinement layer, 3.
...P-type cladding layer, Ri...active layer, j...n
mold cladding layer, 2... cap layer, 76. ?・・・
・Resonator end face. 171 Patent Attorneys Aihiko Fukushi (other names) Ren Figure θ

Claims (1)

[Claims] l Has an internal stripe groove in which the stripe width is wide near the cavity end face and becomes narrower inside the cavity, and the active layer thickness of the crystal layer for laser operation deposited on the stripe groove is A semiconductor laser device characterized in that it is formed thick near the end face.