JPH0430760B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a semiconductor laser device used as a light source for optical information processing.

(Conventional structure and its problems) Semiconductor lasers have many excellent features such as being small, highly efficient, and can be directly modulated by drive current, and have recently been used for optical communication and optical information processing. It has come to be used as a light source.

In order to use it for these purposes, it is necessary that fluctuations in optical output, that is, optical intensity noise, be small. In particular, it is important that light intensity noise is small when the own light is reflected and returned when coupled with an optical system. Furthermore, in order to obtain a minute spot narrowed down to the diffraction limit with a simple lens configuration, the light source is required to have little astigmatism.

Conventional semiconductor lasers, such as the V-groove narrow stripe type semiconductor laser shown in FIG. Since it is a wave type, the oscillation spectrum becomes multi-mode, and noise is small even when there is return light. However, in a gain waveguide laser, the equiphase surface of light inside the resonator is a curved surface, so astigmatism occurs. That is, a difference occurs in the position of the beam waist in the direction parallel to and perpendicular to the joint surface, and the astigmatism difference becomes several tens of μm. In FIG. 1, 1 is an n-type GaAs substrate, 2 is an n-type Al _x Ga _1-x As cladding layer, 3 is a P-type Al _y Ga _1-y As active layer, and 4 is a p-type Al _z
Ga _1-z As clad layer, 5 is n-type Al _u Ga _1-u As layer,
6 is an n-type GaAs layer, 7 is a Zn diffusion region, 8 is a p-side electrode, and 9 is an n-side electrode.

Next, Channeled Substrate as shown in Figure 2
In a planar (CSP) type semiconductor laser, the transverse mode is determined by the effective refractive index distribution formed by absorption of light in the substrate on both sides of the groove. Therefore, the equal phase plane inside the resonator is a plane, and the astigmatism difference is within a few μm, causing almost no problem. However, the oscillation spectrum becomes a single mode, and when there is return light, the noise becomes extremely large, which is a practical obstacle.

(Object of the Invention) In view of the above drawbacks, the present invention provides a semiconductor laser device that has low noise even when there is return light and has a small astigmatism difference.

(Structure of the Invention) In order to achieve this object, the semiconductor laser device of the present invention is provided with two parts that extend from one cavity end face in a direction perpendicular to this end face, are interrupted midway, and are connected to a flat part.
Two parallel ridges are formed on a GaAs substrate.
Al _x Ga _1-x As to fill the gap between the two ridges.
Form a cladding layer, and then sequentially at least Al _y
The structure includes a Ga _1-y As active layer and an Al _z Ga _1-z As cladding layer.

With this configuration, one of the resonators is of the refractive index waveguide type and the other of the resonator is of the gain waveguide type. Therefore, a beam with a flat equiphase surface and no astigmatism is emitted from the index-guided end face.
The spectrum has a high mixing rate of spontaneous emission light into the laser mode in the gain waveguide section, resulting in longitudinal multi-mode oscillation, achieving low-noise operation with small optical intensity fluctuations even in the presence of return light. will be done.

(Description of Examples) Examples of the present invention will be described below with reference to the drawings. FIG. 3 shows a GaAs substrate for constructing a semiconductor laser device in an embodiment of the present invention, and 1a and 1b are two parallel ridges formed on the plane of the substrate, and these ridges are As shown in the figure, it extends from one end surface of the substrate 1 in a direction perpendicular to this end surface, and is interrupted in the middle to be connected to a flat portion. FIG. 4 shows that an n-type Al _x Ga _1-x As cladding layer 2 is formed on the GaAs substrate shown in FIG. 3 so as to fill the groove between the two ridges 1a and 1b, and then p-type Al _y Ga _{1 -y} As active layer 3, p-type Al _z Ga _1-z As
FIG.
1 is a cross-sectional view parallel to the resonator end face on the side where the substrate has a ridge, and FIG.

Next, the operation of the semiconductor laser configured as above will be explained. n-type in contact with p-side electrode 8
The Zn diffusion region 7 of the GaAs cap layer 6 is p-type, and current is injected from there. In the part of the GaAs substrate 1 on the cavity end face side where there are two parallel ridges, the propagation destination generated in the active layer 3 is absorbed by the GaAs in the ridge part, and therefore the propagation occurs in the groove part between the ridges. The effective refractive index for light is higher than the upper portions of the ridges on both sides, forming a refractive index waveguide mechanism. Therefore, in this region, the transverse mode is stabilized, the equiphase plane becomes a plane, and the astigmatism difference of the output beam is within several μm, which is a level that poses no problem in practice. On the other hand, on the side where the board has no ridges,
Since the GaAs substrate is flat and the n-type Al _x Ga _1-x As cladding layer 2 is sufficiently thick, there is no absorption by the substrate, and the transverse mode is caused by the gain distribution formed by the injection carriers. As a result, the gain waveguide mechanism is defined as follows, the rate of spontaneous emission light being mixed into the laser mode increases, and the oscillation longitudinal mode becomes multi-mode.

In this way, within one resonator, a refractive index waveguide mechanism is provided near the output end face of one light to eliminate the astigmatism difference, and a gain waveguide mechanism in the other resonator section provides multi-mode longitudinal mode. ,
Even when there is a return destination, low-noise operation with small fluctuations can be achieved. FIG. 6 is an example of the longitudinal mode spectrum when the optical output of this example is 3 mW.
FIG. 6a shows the results of measuring changes in S/N with temperature in the semiconductor laser device of this example, with the optical output constant (3 mW) and the light feedback rate set at 0.5%.
(Noise frequency 2MHz, bandwidth 300kHz) Similar measurement results of the conventional CSP type laser shown in Fig. 2 are shown in Fig. 6b, but the S/N is significantly higher than that shown in Fig. 6b.
It can be seen that the results have improved.

(Effects of the Invention) As described above, the present invention provides a semiconductor laser substrate with two parallel ridges that are interrupted in the middle, and on which an active layer sandwiched between cladding layers is formed. As a result, it is possible to provide a semiconductor laser that has small astigmatism and operates with low noise even in the presence of return light.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a V-groove narrow stripe type semiconductor laser, FIG. 2 is a sectional view of a CSP type semiconductor laser, FIG. 3 is a perspective view showing an example of the shape of a semiconductor substrate of a semiconductor laser according to the present invention, and FIG. 4 1 shows an embodiment of the semiconductor laser device of the present invention, in which figure a is a cross-sectional view parallel to the resonator end face near the resonator end face, and figure b is a cross-sectional view parallel to the resonator end face at the center of the resonator. ,
FIG. 5 is a diagram showing an example of a longitudinal mode spectrum of an embodiment of the present invention, and FIG. 6 is a diagram showing an example of a longitudinal mode spectrum of an embodiment of the present invention.
It is a figure which shows the temperature change a of N, and the temperature change b of S/N of a conventional example. 1...n-type GaAs substrate, 1a, 1b...ridge,,
2...n-type Al _x Ga _1-x As cladding layer, 3...p-type Al _y
Ga _1-y As active layer, 4... p-type Al _z Ga _1-z As clad layer, 6... n-type GaAs layer, 7... Zn diffusion region, 8... p
side electrode, 9...n side electrode.

Claims (1)

[Claims] 1. _Al Form a Ga _1-x As cladding layer, and then sequentially at least Al _y Ga _1-y
A semiconductor laser device comprising an As active layer and an Al _z Ga _1-z As cladding layer.