JPS6353989A - Semiconductor device - Google Patents

Abstract

PURPOSE:To vary an oscillation wavelength of a semiconductor laser easily while maintaining the state of longitudinal simple mode oscillation thereof by a construction wherein a laminate of a number of specific fundamental units is employed for a part of the structure of a semiconductor laser active layer or a semiconductor laser resonator. CONSTITUTION:A fundamental unit is prepared by laminating five layers of first thin films 1-1 and third thin films 1-3 and by laminating five layers of fourth thin films 1-4 and second thin films 1-2 in such a manner that the film 1-1 and the film 1-4 contact with each other. The refractive index of the films 1-1 and 1-3 is set to be slightly larger than 3. 4, while the refractive index of the films 1-2 and 1-4 is set to be slightly smaller than 3.4. The peak wavelength of a stimulated emission gain of the films 1-1, 1-2, 1-3 and 1-4 is about 1. 3 mum. The stimulated emission gains of a section (a) and a section (b) are made to differ from each other. The fundamental unit thus prepared is employed for a part of the structure of a semiconductor laser active layer or a semiconductor laser resonator. This construction enables the easy variation of an oscillation wavelength of a semiconductor laser.

Description

[Detailed description of the invention] Distributed feedback (DFB) lasers, which are essential for industrial applications and large-capacity optical communications,
The present invention relates to a distributed reflection type (DBR) laser.

2. Prior Art Currently, semiconductor lasers that have an optical periodic structure in their resonator structure, such as DBR lasers and DFB lasers, have become common as semiconductor lasers that can achieve stable longitudinal single mode oscillation (optical Communication device engineering, written by Hiroo Yonezu,
Published by Kogaku Tosho (Reference).

Furthermore, as shown in FIG. 3, a surface-emitting DBR laser has been proposed, which has an optical periodic structure composed of a semiconductor multilayer reflective film 3-1, and an active layer 3-2 and a cladding layer 3-3 laminated on top of the optical periodic structure. (IEICE technical research report 0QE84-
127).

Conventionally, there are two types of optical periodic structures applied to semiconductor lasers: a single-period structure and a single-period structure in which the phase is shifted by wavelength A at the center of the periodic structure. These optical periodic structures are highly effective in realizing stable longitudinal single mode oscillation. In particular, in semiconductor lasers for long wavelength communications,
The effect is remarkable, and normal longitudinal multimode oscillation is suppressed.

Furthermore, even during high-speed modulation, longitudinal single mode oscillation is achieved.

Problems to be Solved by the Invention Although the optical periodic structure conventionally used in semiconductor lasers as described above is highly effective in achieving stable longitudinal single mode oscillation, this structure does not allow longitudinal single mode oscillation. It has been impossible to significantly change the oscillation wavelength while maintaining the oscillation wavelength.

The present invention provides a semiconductor laser having an optical periodic structure that allows the oscillation wavelength to be easily changed while maintaining a longitudinal single mode oscillation state.

Means for Solving the Problems The present invention provides four types of semiconductor thin films, the refractive index of which is approximately equal to the product of the refractive index and the film thickness, and the refractive index of the first thin film and the second thin film, and the refractive index of the third thin film and the third thin film. The refractive index of each of the four thin films is equal, and at the same time, the absorption coefficient of the first thin film and the third thin film or the gain due to stimulated emission, and the absorption coefficient of the second thin film or the optical gain due to stimulated emission due to stimulated emission. The first thin film and the third thin film are stacked alternately so that the total number of layers is an odd number, and the second thin film and the fourth thin film are stacked so that they are in contact with layers with unequal refractive index. A basic unit is a multilayer film in which thin films are alternately stacked so that the total number of layers is equal to the first thin film and the fourth thin film, and a large number of stacked films is used as a semiconductor laser active layer or , the above two problems are solved by using it as a part of the semiconductor laser resonator structure.

Function When the multilayer film according to the present invention is used as a semiconductor laser active layer or a part of a semiconductor laser resonator structure, the oscillation mode is mainly in the first mode described in the claims. a second thin film;
Third. It is determined by the periodic structure due to the refractive index difference between the fourth thin film and the fourth thin film, and longitudinal single mode oscillation is realized. 1st
．． The third thin film is stacked in an odd number of layers, and the second thin film is laminated in an odd number of layers. If there is no difference in absorption coefficient or stimulated emission gain between the stacked odd number of fourth thin films, the transmittance spectrum of this multilayer film, which is closely related to the oscillation mode, will be approximately symmetrical around the oscillation wavelength. . On the other hand, if there is a difference, asymmetry appears in the transmittance spectrum due to interaction between the periodic structure of refractive index difference and the periodic structure of absorption coefficient difference or stimulated emission gain difference. By controlling the magnitude of the difference in absorption coefficient or stimulated emission gain, the degree of asymmetry in the transmittance spectrum can be greatly changed. Since the transmittance spectrum and the oscillation mode are closely related, the appearance of asymmetry in the transmittance spectrum and the change in the degree of asymmetry will cause the wavelength of the oscillation mode to slightly shift from the wavelength determined by the periodic refractive index structure. shift. Even in this case, since the oscillation mode is mainly determined by the periodic refractive index structure, the longitudinal single mode oscillation state remains maintained.

Embodiment FIG. 1 is a conceptual diagram of an embodiment of the present invention. Five layers of the first thin film 1-1 and the third thin film 1-3 are laminated, and the first thin film 1
Six layers of the fourth thin film and the second thin film are laminated so that -1 and fourth thin film 1-4 are in contact with each other, and 110 layers are laminated using this as a basic unit. For example, the refractive index of the first and third thin films is set to 3.
Slightly larger than 4, 2nd. The refractive index of the fourth thin film is 3,4
InG4ASP is slightly smaller. The peak wavelength of stimulated emission gain of each thin film is about 1.3 μm. The film thickness is 0.0956 μm, which corresponds to the A wavelength of 1.3 μm light in the 1nGaAsP thin film. This film thickness control of culmness is fully possible by molecular beam epitaxy and organometallic vapor phase epitaxy.

The stimulated emission gain in the part A in the figure and the mouth part is different. The stimulated emission gain is controlled by injection current or electric field into the A part and the mouth part, and the difference in stimulated emission gain between the A part and the mouth part is controlled.

If this multilayer film is used in the active layer of a semiconductor laser, the fundamental oscillation mode is mainly determined by the refractive index periodic structure, and is 1.3
The oscillation mode is near μm. By changing the stimulated emission gain difference between the A part and the mouth part, the wavelength of the oscillation mode shifts. When the difference in stimulated emission gain is about the same as the threshold average stimulated emission gain, the oscillation wavelength changes by about 0.5%, that is, by about 5 degrees, compared to the case where there is no difference in stimulated emission gain. At this time, the longitudinal single mode oscillation state is maintained.

FIG. 2 is a conceptual cross-sectional view of an active layer portion of an embodiment of a semiconductor laser using the semiconductor multilayer film according to the present invention as an active layer. The multilayer film 3-1 in the figure is made of two types of n-type InGILA with slightly different mixed crystal ratios and refractive indexes, and both of which have peaks of stimulated emission gain at about 1.3 pm! This is a semiconductor multilayer film in which 110 P thin films are alternately laminated. The refractive index of each is approximately 3
．． 4, but slightly different, the film thickness is 0,0, which corresponds to the A wavelength in the InG2 LASP thin film of 1.3 pm light.
It is 956 μm. Film thickness control to this degree is fully possible by molecular beam epitaxy and metal organic vapor phase epitaxy.

A p-type region 2-2 is formed in a part of this multilayer film by impurity diffusion or the like. The multilayer film portion where the boundary region 2-4 between the n-type region 2-3 and the p-type region 2-2 is 2-1 becomes the active layer 2-6. When two types of injection currents with different magnitudes are alternately injected into the active layer composed of this multilayer film every 6 layers, regions with different stimulated emission gains are formed every 5 layers, as shown in Figure 1. Structures are formed in 2-4. A semiconductor laser having this structure oscillates in a stable longitudinal single mode at about 1.3 μm. The difference in stimulated emission gain in the 2-4 region is
When the difference is about % of the threshold average stimulated emission gain, the oscillation wavelength changes by about 0.5%, that is, about 50, compared to the case where there is no difference in the stimulated emission gain. At this time, the longitudinal single mode oscillation state is maintained.

Effects of the Invention If the semiconductor multilayer film according to the present invention is used, the oscillation wavelength of the semiconductor laser can be easily changed while maintaining the longitudinal single mode oscillation state of the semiconductor laser, resulting in a tunable longitudinal single mode semiconductor laser. can be realized. This multilayer film is
It is applicable not only to semiconductor lasers but also to various optical devices.

[Brief explanation of drawings]

FIG. 1 is a conceptual diagram of a semiconductor device according to an embodiment of the present invention, FIG. 2 is a schematic cross-sectional view of a surface-emitting semiconductor laser using a semiconductor multilayer film, and FIG. 3 is a side cross-sectional view of a conventional semiconductor laser. be. 1-1...First thin film, 1-2...Second thin film, 1-3...Third thin film, 1-4...
...Fourth thin film, 2-1...Multilayer film, 2-
2...3-1 p region of multilayer film, 2-3...
...3-1 n region of multilayer film, 2-6... active layer, 2-6... cladding layer, 2-7...
cladding layer. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
figure

Claims (1)

[Claims] The refractive index of the first thin film and the second thin film and the refractive index of the third thin film and the fourth thin film of the four types of semiconductor thin films having substantially the same value multiplied by the refractive index and the film thickness are respectively equal, and The first thin film and the third thin film have the same absorption coefficient or light gain due to stimulated emission, and the second thin film and the fourth thin film have the same absorption coefficient or light gain due to stimulated emission. The first thin film and the third thin film are alternately laminated so that the total number of layers is an odd number, and the second thin film and the fourth thin film are alternately stacked so that they are in contact with layers having unequal refractive index. A semiconductor device characterized in that a basic unit is a multilayer film laminated so that the total number of layers is equal to the lamination of the first thin film and the third thin film, and a large number of these basic units are laminated.