JPH0465887A - Semiconductor laser - Google Patents

Abstract

PURPOSE:To substantially suppress a TM mode component in a semiconductor laser element without using a polarizer by forming a laser structure in an SCH structure, and forming the optical guide layer of the SCH structure in a multiple quantum well structure. CONSTITUTION:It is known that, when two types of media having different refractive indexes are superposed in a laminar state as seen in optical guide layers 6, 8, double refraction is exhibited. The double refraction can be controlled by the number of multiple quantum wells, thickness Lb of a barrier layer film, thickness Lz of a well layer film, etc. The layers 6, 8 are enclosed in a TE mode under the control of the double refraction, and the guide layers may be realized so as not to enclose in the TM mode, thereby cutting OFF in a laser element of the TM mode. Thus, a mode separation which was difficult since the TE mode and the TM mode are near, can be facilitated by introducing the guide layers exhibiting the double refraction, thereby cutting OFF only the TM mode.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a semiconductor laser, and particularly to a semiconductor laser that can suppress oscillation in a specific mode.

[Conventional technology]

Double heterojunction lasers are typically polarized to TE waves. This can be qualitatively explained as follows.

The TE wave has an electric field component within the plane of the active layer, and the TM wave has an electric field component perpendicular to the plane of the active layer. A light wave traveling through a waveguide can be conceptually considered as a collection of plane waves traveling in a zigzag pattern along the waveguide boundary. When considering the reflectance at a reflective surface, TM waves that have an electric field component perpendicular to the reflective surface have a higher reflection than TE waves that have an electric field component within the reflective surface, as can be seen from the existence of the Brewster angle. rate is low. Therefore, since the reflectance of the TE wave is higher than that of the TM wave, in the threshold gain coefficient gth shown by the following formula, gtb:L threshold gain coefficient α, : internal loss R; end face reflectance L : It can be seen that TE wave laser oscillation occurs with a small gain, that is, with a small current, because the resonator length reflection loss becomes small. T.E.
The intensity ratio of the TE wave and the TM wave is 1:1 in a current range sufficiently smaller than the threshold current, but as stimulated emission increases even below the threshold current, the intensity of the TE wave increases. Above the threshold current, if the optical output is 3mW or more, the TE
In many cases, the component ratio between waves and TM waves is 100:1 or more.

In this way, laser light is normally polarized into TE waves, and TM waves.
Although the acid component is small, when it is necessary to further suppress the TM mode component, a polarizing element such as a polarizer or a mode splitter is placed outside the LD to form a module.

[Problems to be Solved by the Invention] As is clear from the above explanation, in conventional semiconductor lasers, in order to suppress the TM mode component, it is necessary to place a polarizing element outside the laser and make it modular. There was a problem in that fine adjustments such as these were required. Also,
Mode selection signal (TE mode/TM
mode) also depends on the performance of the polarizing element, and is essentially 7
There was a problem that the M mode could not be suppressed.

This invention was made in order to solve the above-mentioned problems, and the purpose is to obtain a semiconductor laser that can essentially suppress the TM mode component within the semiconductor laser element (without using a polarizing element). do.

[Means to solve the problem]

The semiconductor laser device according to the present invention has a laser structure of S
CH(Separate Confinement H
The optical guide layer of the SCH structure has a multi-quantum well structure.

[Effect]

In this invention, since the optical guide layer with the SCH structure is a waveguide with a multiple quantum well structure exhibiting birefringence, the conventional T
Since the E mode and the 7M mode are close to each other, mode separation, which was difficult, becomes easier, and since only the 7M mode can be cut off, the TM acid component of the laser beam can be suppressed.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1(a) is a diagram showing the band structure of the SCH structure of a semiconductor laser according to an embodiment of the present invention, and FIG.
It is a figure showing the refractive index distribution of a CH structure part.

In the figure, 21 is p-type A 12 Ga +-2A
S cladding layer, 22 is p-type A j! yCr a t
-y As s-well layer, 23 is p-type A I
I-X As barrier layer, 24 is GaAs active layer, 2
5 is n-type Al, Gap-, As well layer, 26 is n-type A
l2. Cat-g As barrier layer, 27 is n-type A! !
, zG a r-z A s cladding layer. Also, L is the barrier layer thickness, and L is the well layer thickness. A for each layer! The relationship among the composition ratios x, y, and z is z > x > y.

Further, FIG. 2 is a schematic cross-sectional view of the semiconductor laser according to this embodiment. In the figure, 1 is a p-side electrode, 2 is a p-type A1G
aAs cap layer, 3 is a p-type AfGaAs cladding layer,
4 is an n-type AlGaAs current flock layer, 5 is a p-type Aj!
GaAs cladding layer, 6 is p-type AI Ga As
Multi-quantum well light guide layer, 7 is GaAs active layer, 8 is n
type AffiGaAs multi-quantum well light guide layer, 9 is an n-type AlGaAs cladding layer, 10 is an n-type GaAs substrate, 1
1 is an n-side electrode.

Next, the effect will be explained.

It is known that birefringence is exhibited when two types of media with different refractive indexes are stacked alternately in layers, as seen in the light guide layer of this example. This birefringence is determined by the number of multiple quantum wells, the barrier layer thickness Lb, and the well layer thickness L.
It can be controlled by 2 etc. By controlling the birefringence, it is possible to create an optical guide layer that confines the TE mode but does not confine the 7M mode, thereby making it possible to cut off the 7M mode within the laser element. .

As described above, according to this embodiment, conventionally, the TE mode and 7M
Mode separation, which was difficult due to the proximity of the modes, becomes easier by introducing a light guide layer exhibiting birefringence, and it becomes possible to cut off only the 7M mode.

Note that although a GaAs-based semiconductor was used in the above embodiment, the present invention is also effective even if other semiconductors are used.

Further, in the above embodiments, current confinement is performed using a current blocking layer, but it goes without saying that this method is not the only method for forming narrow stripes in the active region.

〔Effect of the invention〕

As described above, according to the present invention, since the light guide layer of the SCH structure has a multiple quantum well structure, only the TM mode can be cut off by appropriate waveguide structure design, and the TM mode component of the laser light can be cut off. This has the effect of suppressing the

[Brief explanation of drawings]

FIG. 1 shows an SC of a semiconductor laser according to an embodiment of the present invention.
FIG. 2 is a cross-sectional view showing a semiconductor laser according to an embodiment of the present invention. 1 is a p-side electrode, 2 is a p-type AfGaAs camp layer, 3 is a p-type Aj2GaAs cladding layer, and 4 is an n-type Aj2GaA
s barrier layer, 5 is a p-type AlGaAs cladding layer, 6 is a p-type Aj2GaAs multiple quantum well light guide layer, 7 is Ga
As active layer, 8 is n-type A! GaAs multiple quantum well light guide layer, 9 is n-type AffiGaAs cladding layer, 1
0 is an n-type GaAs substrate, 11 is an n-side electrode, 21 is a P-type A
lz Ga1-z As cladding layer, 22 is p-type Al
y Ga + - y A s well layer, 23 is p-type A
f, Ga, -, As barrier layer, 24 is GaAs active layer,
25 is n-type Aj2yGa+, As well layer, 26 is n-type AlXGa, -8As barrier layer, 27 is n-type Aff□G
a, -z As cladding layer, L, barrier layer thickness, +2
is the well layer thickness. Note that the same reference numerals in the figures indicate the same or equivalent parts.

Claims (1)

[Claims] (1) SCH (Separate configuration)
tHetero-structure) structure, wherein the light guide layer of the SCH structure is composed of a multiple quantum well layer, and the oscillation of a specific mode is suppressed by the birefringence exhibited by the multiple quantum well layer. .