JPS5990982A - Semiconductor laser element - Google Patents

Abstract

PURPOSE:To obtain the novel available semiconductor laser element, which prevents the increase of noises while having a gain waveguide mechanism and in which a coupling with an optical system can be improved, by providing a refractive index waveguide mechanism and executing a vertical multi-mode oscillation. CONSTITUTION:A current confining layer 2 consisting of N-GaAs for limiting a current path, a P type clad layer 3 consisting of P-GaAlAs, an active layer 4 and an optical guide layer 5 consisting of P or N-GaAlAs (or GaAs), an N type clad layer 6 consisting of N-GaAlAs, and a cap layer 7 consisting of N-GaAs are laminated on a P-GaAs substrate 1 in succession through a liquid epitaxial growth method. A P side electrode consisting of Au-Zn is evaporated and formed to the GaAs substrate 1 and an N side electrode consisting of Au-Ge-Ni-Au to the cap layer 7. Accordingly, currents do not flow through a region, to which the current confining layer 2 interposes, because it is joined at negative polarity, and only a striped groove section from which the current confining layer 2 is removed functions as a current path.

Description

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

<Prior art> Conventionally, when a semiconductor laser device is used as a light source for a disk device, when coupled with the optical system of a video disk or audio disk, the return light of the output laser beam due to reflection from the disk surface is transmitted to the semiconductor laser device. As a result, the linearity between the injected current and the optical output decreases as shown by the solid line in Fig. 1 due to the interference of the re-incoming light with the output light, and the linearity between the injected current and the optical output decreases as shown by the solid line 11 in Fig. 2. As shown, the noise of the output light may increase, making it impossible to put it into practical use. As a means to solve this problem, the current injection width, that is, the stripe width, is made narrower than the usual 10 to 15 μm, to about the carrier diffusion length in the active layer, that is, about 2 to 4 μm, to prevent the occurrence of distortion or increase in return optical noise. Attempts are being made to avoid it.

In such a semiconductor laser, the optical distribution of the laser is determined by the gain distribution, but since the cavity volume is small, the participation of the spontaneous emission laser mode becomes large, and the injection current density is large, so the gain spectral width is expanded,
The multi-axis mode oscillation reduces the influence of re-incident light.

However, the near-field image of a semiconductor laser element with a gain waveguide mechanism changes due to injection current or changes over time, making the coupling with the optical system unstable and causing large astigmatism, making it difficult to connect with optical systems such as lenses. This results in disadvantages such as reduced coupling efficiency.

<Objective of the Invention> The present invention fundamentally solves the above-mentioned drawbacks of conventional semiconductor laser devices, and has a refractive index waveguide mechanism and longitudinal multi-mode oscillation to reduce noise. It is an object of the present invention to provide a new and useful semiconductor laser device that can prevent the increase in gain and improve the coupling with an optical system in a semiconductor laser device having a gain waveguide mechanism.

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

n to limit the current path on the 1'-GaAs substrate l
- Current confinement layer 2 made of GaAs, P-GaAeA
P-type cladding layer 3 consisting of s) or electron 1-GaA
An active layer 4 and a light guide layer 5 made of eAs (or GaAs), n-GaAj? An n-type cladding layer 6 made of As and a cap layer 7 made of n-GaAs are sequentially laminated by liquid phase epitaxial growth. Note that 8 and 9 in the figure are respective end faces of the laser resonator. The thickness of the current confinement layer 2 is about 0°3 um, and after depositing it on the GaAs substrate 1, a stripe-shaped groove is formed from the surface to the GaAs substrate 1 to a depth of about]/'m as described later.
A current path is formed by etching. Ga
A P-side electrode made of Au--Zn is deposited on the As substrate 1, and an n-side electrode made of Au-Ge-Ni-Au is deposited on the cap layer 7.

Since the region where the current confinement layer 2 is interposed is connected with opposite polarity, no current flows, and only the striped groove portion from which the current confinement layer 2 is removed serves as a current path.

FIG. 4 is a cross-sectional view taken along the line AA in FIG. 3, showing the cross-sectional structure of the resonator end face. Further, FIG. 5 is a sectional view taken along line BB in FIG. 3, showing the sectional structure inside the resonator.

Inside the resonator, the width W1 of the sliver groove formed in the current confinement layer 2 is 6 JLm, and the length of the stripe groove having the width W1 is 20 JLm. Under the influence of the stripe grooves, the active layer 4 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 2 is set to 4 μm, and the length is set to 200 μm. Note that the center line of the stripe groove matches the end face of the resonator internally. The active layer 4 in this portion is flattened and is not affected by the shape of the stripe groove.

FIG. 6 is a perspective view showing a shape in which a current confinement layer 2 is grown on a GaAs substrate 1 and striped grooves are formed in one photoetching process.

When the P-type cladding layer 3 is epitaxially grown in the state shown in FIG. 6, 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, so more P-GaA6As is required to fill this groove portion. Therefore, this P-type cladding layer 3
The active layer grown thereon becomes as shown in FIGS. 4 and 5 depending on the top surface shape of the P-type cladding layer 3. With this structure, there is a large lateral refractive index difference at the cavity end face, and the light beam is focused on a very small diameter spont of 171 m or less, but inside the cavity, the lateral refractive index difference is large. Since the difference becomes smaller, the light spreads by 3 to 4 tim in the horizontal direction.

In the laser device having the above structure, the aluminum alloy ratios a, b, c, and d of the P-type cladding layer 3, the active layer 4, the optical guide layer 5, and the through-type cladding layer 6 are, for example, as follows.

a=0.65...P-type cladding layer +=0.15...active layer c=0.35...light guide layer d=0.45...n-type cladding layer, 2 The mixed crystal ratio of the P-type cladding layer 3 is set large so that the mixed crystal ratio of the two cladding layers is asymmetrical. By doing this, the leaked light from the active layer 4 is generated in the direction of the light guide layer 5, so that it hardly deviates to the substrate side, and the current distribution in the lateral direction is the same as in a normal electrode stripe laser. Since the wave is guided by a gain corresponding to , longitudinal multimode oscillation is performed. However, since the thickness of the active layer changes in the lateral direction at the resonator end face, the wave is guided by the difference in refractive index, and therefore, the beam waste is coincident with the end face, 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. 8 is a spectrum diagram of the semiconductor laser device shown in FIG. 3.

The semiconductor laser device shown in FIG. 3 oscillated in longitudinal multimode up to a DC output of 20 mW, and had an astigmatism of 5/Am or less.

As described in detail above, according to the present invention, longitudinal multi-mode oscillation is achieved, and the injection current versus light output characteristic with good linearity is obtained with less influence of light returning to the laser end face. Moreover, the astigmatism is small and the coupling efficiency with the optical system is good. Furthermore, stable output light can be obtained without changing the near-field image due to injection current or changes over time.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the injection current versus optical output characteristic of a conventional semiconductor relay wire. The solid line is the characteristic curve when there is re-incoming light, and the broken line is the characteristic curve when there is no re-entering light U=1. FIG. 2 is a noise characteristic diagram of a conventional semiconductor laser device. Curve 11 is a characteristic curve when there is re-incident light, and curve 42 is a characteristic curve when there is no re-incident light. FIG. 3 is a cross-sectional view of the structure of a semicircular body->J element showing one embodiment of the present invention. FIG. 4 is a sectional view taken along line A-A in FIG. 3. FIG. 5 is a sectional view taken along line B-B in FIG. 3. 6th
This figure is a detailed perspective view of essential parts showing the substrate structure of the semiconductor laser device shown in FIG. 3. FIG. 7 is a characteristic diagram showing the current versus optical output characteristics of the semiconductor laser device shown in FIG. 3. FIG. 8 is a spectrum diagram of the semiconductor laser device shown in FIG. 3. 1...GaAs substrate, 2...Current confinement layer, 3...
- P-type cladding layer, 4... active layer, 5... light guide layer, 6... n-type cladding layer, 7... Kihe knob layer, 8,
9...Resonator end face. Agent Patent attorney Aihiko Fukushi (and 2 others) Figure 1 Biting Koi' - Yorker 2r Figure 2

Claims (1)

[Claims] 1. The active layer thickness of the crystal layer for laser operation deposited on the stripe groove, which has a partial stripe groove for current confinement where the stripe width is wide near the cavity end face and narrower inside the cavity. What is claimed is: 1. A semiconductor laser device characterized in that a light guide layer is formed thickly near a resonator end face, and a light guide layer is superimposed on an active layer.