JPH05875B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Technical Field> The present invention relates to a semiconductor laser device in which interference noise due to returned light is reduced.

<Prior art> Conventionally, when a semiconductor laser device is used as a light source for a disk information processing device,
When coupled with an optical system such as an audio disk, the return light of the output laser beam due to reflection from the disk surface may be re-injected into the semiconductor laser element. The linearity between the injected current and the optical output decreases as shown by , and the noise of the output light increases as shown by the solid line ₁ in FIG. 2, so that it may become impossible to put it into practical use. As a means of solving this problem, the current injection width, that is, the stripe width, was
Attempts have been made to narrow the distance from 15 μm to about the carrier diffusion length in the active layer, that is, about 2 to 4 μm, in order to avoid the occurrence of distortion or increase in return optical noise.
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 The beam is enlarged and oscillated in a multi-axis mode, and the influence of re-incident light is reduced by this multi-axis mode oscillation.

However, the near-field image of semiconductor laser elements 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. This results in disadvantages such as reduced coupling efficiency with the optical system.

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

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

A current confinement layer 2 made of n-GaAs for controlling the current path on a p-GaAs substrate 1, a p-
p-type cladding layer 3 made of GaAlAs, p or n-
Active layer 4 made of GaAlAs (or GaAs), n-
n-type cladding layer 5 made of GaAlAs, n-GaAs
A cap layer 6 consisting of the following is sequentially laminated by a liquid phase epitaxial growth method. Note that 7 and 8 in the figure are respective end faces of the resonator. The thickness of the current confinement layer 2 is approximately 0.8 μm, and after being deposited on the GaAs substrate 1, striped grooves are formed from the surface as described later.
Etching is performed to a depth of approximately 1 μm until reaching the GaAs substrate 1 to form a current path. The GaAs substrate 1 has a P-side electrode made of Au-Zn and a cap layer 6.
An n-side electrode made of Au-Ge-Ni-Au is formed by vapor deposition. 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 end portion of the resonator. Also, Figure 5 is B of Figure 3.
-B is a cross-sectional view showing the cross-sectional structure inside the resonator.

At the end of the resonator, the width W ₁ of the stripe groove formed in the current confinement layer 2 is 6 μm, and the length of the stripe groove with the width W ₁ is 20 μm. 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 W ₂ of the stripe groove formed in the current confinement layer 2 is 4 μm, and the length is
It is set to 200μm. 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 photo-etching 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 region of stripe width W ₂ , and a depression is formed on the upper surface in the region of stripe width W ₁ . be done.
This is because the groove width is wider in the stripe width W ₁ area, so the p-GaAlAs required to fill this groove part is
This is due to an increase in Therefore, the active layer 4 grown on the p-type cladding layer 3 has a shape as shown in FIGS. 4 and 5, depending on the top surface shape of the p-type cladding layer 3. With this structure, the active layer 4 is formed convexly into the stripe groove at the cavity end face, so the difference in refractive index in the lateral direction is large, and the light beam has a very small diameter of 1 μm or less. Although the light is focused on a spot, the difference in refractive index in the lateral direction becomes small inside the resonator, so the light is
Spreads 4μm.

In this device, the respective mixed crystal ratios x, y, and z of the p-type cladding layer 3, active layer 4, and n-type cladding layer 5 are as follows: x=0.50 (p-type cladding layer) y=0.15 (active layer) z= 0.45 (n-type cladding layer), and the mixed crystal ratio of the p-type cladding layer 3 is set to be asymmetric. 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 as in a normal electrode stripe laser, the light is guided by the gain, resulting in longitudinal multimode oscillation. However, at the resonator end face, since the thickness of the active layer changes in the lateral direction, the waves are guided by the refractive index, and therefore the beam waists coincide at 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 shown in Figure 3 oscillates in longitudinal multimode up to a DC output of 15 mW, and has no astigmatism.
It was less than 5 μm.

<Effects of the Invention> As detailed above, according to the present invention, longitudinal multi-mode oscillation is achieved, and injection current versus light output characteristics with good linearity are obtained with less influence by light returning to the laser end face. Furthermore, 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 the drawing]

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 re-incident light, and the broken line is the characteristic curve when there is no re-incident light. FIG. 2 is a noise characteristic diagram of a conventional semiconductor laser device. Curve ₁ is when there is re-incoming light,
Curve 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. Figure 4 is A-A of Figure 3.
FIG. FIG. 5 is a sectional view taken along line BB in FIG. 3. FIG. 6 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. 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...n-type cladding layer, 6...cap layer, 7, 8...resonator end face.

Claims (1)

[Claims] 1 It has an internal stripe groove for current pinching in which the stripe width is wide near the cavity end face and narrower in the inside of the cavity, and the active layer of the crystal layer for laser operation deposited on the stripe groove is It is formed flat inside the cavity and convexly into the stripe groove near the cavity end face, so that the lateral refractive index difference at the cavity end face is larger than that inside the cavity. A semiconductor laser device.