JPS62202582A - Integrated semiconductor laser - Google Patents

Abstract

PURPOSE:To vary equivalent refractive indice Ne, i.e., propagation constants, of respective waveguides and make the waveguide with a larger equivalent refractive index have a smaller propagation loss alpha and obtain a high output light beam by a method wherein a distance between a layer which functions as an absorbing and reflecting element for a guided light and an active layer is gradually varied every one of parallel stripes. CONSTITUTION:A quintuplex-stripe part 14 is an inclined active layer which is formed with an inclination against a current blocking layer 2 so as to make a distance between the active region and the absorbing region (current blocking layer) varied every waveguide. By this injection of a current, the parts of the active layer above the stripe shape trenches 8 are turned into active regions and five elements make oscillation while being coupled with each other. As the larger the distance between the inclined active layer 14 and the current blocking layer 2, the smaller the influence of absorption and reflection of the layer 2 in the region where a P-type AlGaAs lower cladding layer 3 is relatively thin, an equivalent refractive index Ne is large and a propagation loss alpha is small. By the effect that light converges into the part where an equivalent refractive index Ne is large, the shape of the light distribution of a basic array mode is biased to the left and the propagation loss alpha becomes smaller toward the left side. In other words, the mode gain to the basic array mode becomes larger than the mode gain to a higher degree mode so that the lateral mode of the integrated laser can be controlled to be the basic mode.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an integrated semiconductor laser (hereinafter simply referred to as an integrated laser), and relates to transverse mode control thereof.

[Conventional technology]

FIG. 4(a) shows an example of a conventional integrated laser, which has a structure in which five so-called internal stripe lasers are arranged in parallel. A laser similar to that shown in FIG. 4 differs in that it has a waveguide layer without a current blocking layer, but is described in, for example, the document ^ρp1. Phys, Lett.

43 pp. 1096-1098''.

In the figure, 1 is a p-GaAs substrate, 2 is an n-GaA substrate
s current blocking layer, 3 is p-A ff1GaAs lower cladding layer, 4 is p-Aj! To Ga8S activity, 5 is n-A/!
GaAs upper cladding layer, 6 is an n-side electrode, 7 is a p-side electrode,
Reference numeral 8 denotes a striped groove penetrating the current blocking layer 2 .

Next, the operation will be explained. When a positive voltage is applied to the p-electrode 7 and a negative voltage is applied to the n-electrode 6, current flows through the striped grooves 8 and is injected into the active layer 4 above the grooves. When the injection is increased, population inversion of carriers occurs in the upper part of the groove in the active layer 4 (active region), and light emission occurs due to stimulated emission. The light thus generated is guided along the stripes, and oscillates due to amplification and feedback effects similar to those of a normal semiconductor laser. Figure 4 (bl, (C1 is the equivalent refractive index Ne in the lateral direction and the propagation loss α for guided light, respectively)
These distributions form equivalent and parallel waveguides in the active layer 4 on the five grooves 8.

The integrated laser in question here is a phase-locked laser in which each element oscillates at the same wavelength while maintaining a constant phase relationship due to the interaction of guided light in the plurality of waveguides. For this purpose, the interval between each element (stripe) is narrowed to about several μm to achieve optical coupling. This type of laser has the advantage that the output can be increased by increasing the area of the entire light emitting group while maintaining optical coherence.

[Problem that the invention seeks to solve]

Conventional integrated lasers are composed of five elements (waveguides, paths) equivalently, so the difference in propagation constant of the eigenmodes (array modes) of the five integrated lasers as a whole is small, and The mode gain for the fundamental mode in which all waveguides are in phase is not necessarily high. For this reason,
There was a drawback that the transverse mode was not controlled to the fundamental mode, and the output beam had a bimodal or complicated shape. Furthermore, in order to block higher-order modes with the conventional structure, there is a problem in that microfabrication is required to make the width and spacing of the stripes 1 μm or less.

This invention was made to solve the above problems, and by controlling the array mode of the integrated laser to the fundamental mode, the output beam is controlled to be a single peak with a narrow half width in the horizontal direction. The purpose of this study is to obtain an integrated laser with high optical output.

[Means for solving problems]

The integrated laser according to the present invention absorbs and absorbs guided light.
By gradually changing the distance between the layer that acts as a reflector and the active layer for each stripe arranged in parallel, the equivalent refractive index Ne of each waveguide, that is, the propagation constant, is changed, and the waveguide with a larger equivalent refractive index has a higher propagation rate. This is designed to reduce the loss α.

[Effect]

In this invention, since each waveguide has a different propagation constant as a single unit, the difference in the propagation constant of each array mode when integrated becomes large, and the stripe interval at which higher-order modes are blocked becomes large. Further, since the propagation loss for the fundamental mode is the smallest, even if there is no difference in the injection current, the mode gain of the fundamental mode is the largest, and the transverse mode of oscillation is controlled to the fundamental mode.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. 1st
In the figure, the same reference numerals as in FIG. 4 indicate the same or corresponding parts. 11 is made of p -GaAs (l OO) with a plane orientation tilted perpendicular to the stripe from the (100) plane.
The off-substrate 14 is a slanted active layer which is formed in five series of stripes and is inclined with respect to the current blocking layer 2, and the interval between the active region and the absorption region (current blocking layer) in each waveguide is different. be.

A specific method for realizing this structure is as follows.

FIG. 2(a) shows the (100) off-board 11 and stripe 8.
FIG. p-GaAs substrate 1
1 and the current blocking layer 2 have planes that are shifted from the <100> direction to the 011> direction by a small angle θ (5°), and the stripes 8 are parallel to the <011> direction, which is perpendicular to the <011> direction. It is. The figure (bl) is a schematic cross-sectional view of the (011) plane after the lower cladding layer 3 and the graded active layer 14 are grown in liquid phase on the substrate 1 and the current blocking layer 2. 1
00) There is a microscopic step on the surface that deviates from the surface,
Growth occurs when this step moves in the <Ol 1> direction. For this reason, while the grown layer is thin, a relatively large difference in layer thickness occurs on both sides of the stripe portion, and as a result, the active layer in the stripe portion is formed to be inclined. Note that 21 in FIG. 2 indicates a normal line to the substrate 11.

Next, the effects will be explained. By current injection, the active layer located on the striped groove 8 becomes an active region, and the five elements are coupled to each other and oscillate.
This is the same as the conventional example shown in FIG. The difference is the equivalent refractive index Ne and propagation loss α of each element, as shown in Figure 1 (
b) and (C) show the distributions of Ne and α in the lateral direction, corresponding to FIG. When the p-AlGaAs lower cladding layer is thin (<1 μm) to a certain extent, the graded active layer 1
The farther the layer 4 is from the current blocking layer 2, the smaller the influence of absorption and reflection by the layer 2, the larger the equivalent refractive index Ne and the smaller the propagation loss α. The asymmetry of the distributions in Figures 1(b) and 1(C) is based on this effect. When each waveguide is equivalent as in the conventional example, the fundamental array mode has a symmetrical light distribution with the maximum at the center, but the equivalent refractive index N
Due to the effect that light is concentrated in the portion where e is high, the light distribution in the fundamental array mode of this embodiment is biased to the left, and as shown in tc+ in the figure, the propagation loss α is smaller toward the left. That is, the monido gain for the basic array mode is
The transverse mode of the integrated laser can be controlled to the fundamental mode, with the gain greater than the gain for higher-order modes.

Therefore, in this embodiment, higher-order modes can be easily blocked without finely processing the stripe width and spacing as in the conventional method. Furthermore, since fundamental mode oscillation is selected, a light beam with a very narrow horizontal emission angle and high output can be obtained.

In the above example, the p-GaAs substrate was (10
0), a current blocking layer 32 having a thick one side of the multiple stripe portion may be used as shown in FIG. In this case as well, if the lower cladding layer 3, the active layer 14, and the upper cladding layer 5 are sequentially grown on the above structure by liquid phase growth, the active layer 14 tilted on the stripe portion can be formed, and the same effects as in the above embodiment can be achieved.

Further, in each of the above embodiments, the case of an internal stripe type laser in which the layer acting as an absorber also serves as a current blocking layer has been described, but a CS P laser that does not have a current blocking function has been described.
(Channeled-Substrate-Plan
An ar) type laser may also be used, and the same effects as in the above embodiments can be achieved.

〔Effect of the invention〕

As described above, according to the integrated semiconductor laser according to the present invention, the equivalent refractive index of each element, that is, the propagation constant,
Since the structure has different propagation losses, it is easy to block higher-order eigenmodes, and since the fundamental mode oscillation is selected, a high-output optical beam with a very narrow horizontal emission angle can be obtained. It has the effect of

[Brief explanation of drawings]

FIG. 1(a) is a cross-sectional front view of an integrated semiconductor laser according to an embodiment of the present invention, and FIGS. 1(b) and 1(C) are perspective views showing a method of manufacturing the integrated semiconductor laser according to the embodiment. , FIG. 3 is a cross-sectional front view for explaining another manufacturing method, FIG. 4(a) is a cross-sectional front view of a conventional integrated semiconductor laser, FIG. 4(b), (C ) are diagrams showing the equivalent refractive index distribution and propagation loss distribution of the laser, respectively. 11... (100) off-substrate, 14... graded active layer, 2.32... current blocking layer (absorption layer). Note that the same reference numerals in the figures indicate the same or equivalent parts. Applicant: Director of the Agency of Industrial Science and Technology Todoroki Datsu Figure 1 (C) Figure 2 (b) Figure 3 32: πノ, 茫 MJI: See Figure 4 procedural amendment (voluntary) Showa//2016/-2/2011 Noyu Day

Claims (4)

[Claims] (1) In a phase-locked integrated semiconductor laser in which two or more waveguides are provided adjacently, each waveguide has a propagation constant corresponding to a fundamental mode when viewed as a mutually different single unit, and the propagation constant is An integrated semiconductor laser is characterized in that the higher the waveguide, the lower the propagation loss. (2) The integrated circuit according to claim 1, wherein the active layer is formed at an angle with respect to the absorption layer so that the distance between the active region and the absorption region in each waveguide is different. type semiconductor laser. (3) The tilted active layer is formed by liquid phase growth on a {100} off-substrate having a plane orientation that deviates from {100} by a small angle in the direction of rotation around the waveguide direction. An integrated semiconductor laser according to claim 2, characterized in that: (4) The inclined active layer is formed by liquid phase growth on an absorption layer having a difference in layer thickness on both sides of the plurality of waveguides. Integrated semiconductor laser.