JPH0430759B2 - - 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 capable of direct modulation by drive current, and have recently been used in optical communications and optical information. It has come to be used as a light source for processing.

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. In order to obtain a minute spot narrowed down to the diffraction limit with a simpler 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 several μm.
Within this range, there is almost no problem. However, the oscillation spectrum becomes a single mode, and when there is return light, the noise becomes very large, which is a practical obstacle.

(Object of the Invention) In view of the above drawbacks, it is an object of the present invention to provide 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 has two parallel ridges protruding on a plane, and a semiconductor laser device is provided on a GaAs substrate in which these ridges are interrupted at the center in the longitudinal direction. Then, an Al _x Ga _1-x As cladding layer, an Al _y Ga _1-y As active layer, and an Al _z Ga _1-z As cladding layer were sequentially formed to fill the groove formed between the two ridges. It is structured as follows.

With this configuration, the resonator is of the refractive index waveguide type near the end face, and the gain waveguide type is in the center of the cavity, thereby creating an intermediate state between the gain waveguide type and the refractive index waveguide type. This makes it possible to realize a semiconductor laser having multiple longitudinal modes and a relatively small astigmatism difference.

(Description of Examples) Examples of the present invention will be described below with reference to the drawings. FIG. 3 shows an n-type laser beam for configuring a semiconductor laser device according to an embodiment of the present invention.
This figure shows a GaAs substrate, and 1a and 1b are two parallel ridges formed on the plane of the substrate, and these ridges are interrupted at the center in the longitudinal direction as shown. FIG. 4 shows that an n-type Al _x Ga _1-x As cladding layer 2 is formed on the n-type 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
A semiconductor laser is shown in which an As cladding layer 4, an n-type GaAs layer 6, a p-side electrode 8 are formed, and an n-side electrode 9 is formed on the bottom surface of the substrate. Fig. 3b shows a cross-sectional view parallel to the resonator end face at the center of the resonator.

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 layer 6 is p-type, and current is injected from there. on the resonator end face side
In a part of the GaAs substrate 1 with two parallel ridges, the propagating light generated in the active layer 3 is absorbed by the GaAs in the ridge part, and therefore the effective refractive index for the propagating light in the groove part between the ridges is is higher than the tops 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, in the center of the resonator, GaAs
Since the 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 defined by the gain distribution formed by the injection carriers. This results in a gain waveguide mechanism in which the rate of spontaneous emission light 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 light output end face to eliminate astigmatism difference, and a gain waveguide mechanism inside converts the longitudinal mode into multiple modes, and the returned light It is possible to achieve low-noise operation with small fluctuations even when there is a problem. FIG. 6 is an example of the longitudinal mode spectrum when the optical output of this example is 3 mW. Figure 6a shows the semiconductor laser device of this example with a constant optical output (3 mW), a light feedback rate of 0.5%, and an S/N ratio of 0.5%.
These are the results of measuring temperature changes. (Noise frequency
2MHz, bandwidth 300kHz) Similar measurement results for the conventional CSP type laser shown in Fig. 2 are shown in Fig. 6b, and it can be seen that the S/N is significantly improved compared to this.

(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. Thus, 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.
FIG. 6 is a diagram showing a temperature change a of N and a temperature change b of S/N of a conventional example. 1, 6...n-type GaAs substrate, 1a, 1b...ridge, 2...n-type Al _x Ga _1-x As clad layer, 3...p-type
Al _y Ga _1-y As active layer, 4... p-type Al _z Ga _1-z As cladding layer, 7... Zn diffusion region, 8... p-side electrode, n-side electrode.

Claims (1)

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