JPH0376287A - Broad area laser - Google Patents

Abstract

PURPOSE:To obtain a broad area laser controllable in oscillation lateral mode and excellent in mass productivity by a method wherein an equivalent refractive index in a direction parallel to a PN junction is so set as to decrease in steps starting from the center of an optical waveguide toward its ends. CONSTITUTION:Equivalent refractive indexes of regions are so set as to satisfy a formula, region C<region B<region A. As mentioned above, if an equivalent refractive index is so set as to decrease in steps starting from the center of an optical waveguide toward its ends, induced light is liable to collect at the center of the optical waveguide and a filament oscillation can be prevented. In the region C, light induced in an active layer oozes out slightly to a cap layer 7 and absorbed. When the thickness t1 of a clad layer 6 provided under the cap layer 7 is equal to 0.4mum or below, the region C increases in light absorption to increase an oscillation threshold and to decrease an external differential quantum effect. On the other hand, if t1 is larger than 0.7mum, light is prevented from reaching the cap layer 7 and there is no substantial difference between the region C and the region B. Therefore, it is desirable that t1 is set to satisfy a formula, 0.4mum<=t1<=0.7mum.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a semiconductor laser having a light emission width of several tens to several hundreds of micrometers and used for optical information processing, laser processing, and the like.

BACKGROUND OF THE INVENTION As the field of application of the above-mentioned semiconductor lasers has expanded, the demand for higher output semiconductor lasers has increased in recent years. Semiconductor laser arrays and broad area lasers are currently known as devices capable of producing watt-class optical output.

The former method shortens the distance between waveguides, installs many waveguides in parallel, couples laser light between adjacent waveguides, and synchronizes the positions of all waveguides to achieve high output. This is what we aim to do.

However, such a configuration has problems in that the far field pattern often has two peaks and the manufacturing process becomes complicated.

On the other hand, in the latter case, the waveguide width is widened to several tens to hundreds of micrometers, and the light emitting area of the laser emitting end face is increased to achieve high output. Since it has such a simple structure, it has the advantage that the manufacturing process can be simplified compared to the former.

However, since the oscillation transverse mode is multi-mode or filament oscillation, there is a problem that light cannot be focused on a small spot. Therefore, in terms of applications, it has been limited to use as an energy source.

Therefore, it is necessary to control the oscillation transverse mode of a broad area laser.
1 (fundamental mode), it has been proposed to provide a high reflection portion at the center of the front end face (Laser Society Research Group Report RTM-88-25).

However, since such a structure requires microfabrication on the end face, it becomes difficult to manufacture and has a problem in that it lacks mass productivity.

The present invention has been made in view of the current situation, and it is an object of the present invention to provide a broad area laser that enables control of the oscillation transverse mode and is excellent in mass production.

° In order to achieve the above-mentioned object, the present invention provides a broad area laser having a large waveguide width, in which the equivalent refractive index of the pn junction and the horizontal direction is stepped from the center of the waveguide toward both ends. It is characterized by being formed to be small.

The present invention also provides a broad area laser in which a cladding layer is formed on an active layer of a waveguide, in which the active layer is located approximately 0°4 to 0.7 μm above the cladding layer, excluding the central portion of the waveguide. The present invention is characterized in that a semiconductor layer is formed which is of a conductivity type that allows current injection and has a large absorption coefficient for the oscillation wavelength.

Furthermore, the present invention is characterized in that, in a broad area laser having a large waveguide width, the amount of carriers injected into the center of the waveguide is larger than the amount of carriers injected at both ends.

Since conventional broad area lasers do not have a difference in refractive index in the direction parallel to the pn junction within the waveguide, many transverse modes are generated in addition to the fundamental transverse mode, as shown in Figure 4. This results in so-called multi-mode oscillation, or filamentary oscillation due to slight irregularities in composition or film thickness.

However, if the equivalent refractive index decreases stepwise from the center of the waveguide toward both ends as in the first invention, the generated light will not gather at the center of the waveguide, as shown in FIG. It is possible to prevent breakage and filament oscillation.

Further, according to the second invention, oscillation due to the fundamental transverse mode is likely to occur for the reasons described below.

That is, the m-th transverse mode gain is generally expressed by the following equation (1), but as shown in Figure 1, the optical intensity of the higher-order mode has a large peak in the region closer to the end than in the center of the waveguide. ing.

1s (y): Light intensity in the active layer in the horizontal direction with respect to the junction In this case, as in the second invention, a large absorption coefficient with respect to the oscillation wavelength is provided at a portion at a predetermined distance from the active layer at the end of the waveguide. If a semiconductor layer is provided, part of the light generated in the region near both ends of the waveguide will be absorbed by the semiconductor material. Therefore, as shown in FIG. 3, since the gain is suppressed in these regions, the mode gain of the higher-order mode becomes smaller than that of the fundamental mode, and oscillation due to the fundamental transverse mode is more likely to occur.

If the amount of carrier injection into the central portion of the waveguide is larger than that in other regions as in the third aspect of the invention, the amount of current flowing into the central portion of the waveguide will be large and oscillation will occur more easily. Moreover, at this time,
As shown in FIG. 4 above, there is a peak of light intensity in the fundamental transverse mode at the center of the waveguide. Therefore, according to the third invention, the fundamental transverse mode is in a state where it is most likely to oscillate.

An embodiment of the direct-operation member of the present invention will be described below with reference to FIG.

As shown in Figure 1, n-type GaAs with (100) plane orientation
On the surface of the substrate 1 consisting of
a, ssA j! 41. Cladding layer consisting of 41AS (Se-doped, n-5XIO"(:II-')
2 and 0.08 μm thick Gas, weA le,
An active layer (non-doped) 3 made of ohAs and a thickness of 0
．． A cladding layer (Zn doped, p-2X10"3-
”) 4 are formed in this order. On a part of the cladding layer 4, p-type Gas, ?oA II o, x5A
A light guide layer [Zn doped, p=2xlon value 3] 5 is formed of p-type Ga.
A cladding layer consisting of (Zn doped, p wr 2
XIO"cs-co] 6 is provided. This cladding layer 6 has a thickness (t
g -2゜0/Jm) is the thickness of the edge in the figure (t+-0,4
μm>. On the cladding layer 6 is a cap layer (Zn doped, 1) made of p-type GaAs with a thickness of 0.5 μm.
” ) 7 is formed, and an insulating layer 8 that is exposed to Si 02 is provided in a portion of the cap layer 7 other than the current injection portion. A front electrode 9 is provided on the surface opposite to the camp layer 7, and a back electrode 10 is formed on the back surface of the substrate 1.

Note that the light guide layer 5 in the cladding layer 6 and the cap layer 7
A Zn diffusion region 11 is formed in which the carrier concentration is increased by Zn diffusion, and this Zn
The depth of the diffusion region 11 is 0.5 to 0.7 μm at the bottom of the tank.

In addition, in the above embodiment, the current injection width (the width of the area where the slot layer 8 is not provided) WI is 150 μm, and the width of the area where the craft layer 6 is raised (the width of the area where absorption loss is small) W2 is 90 μm 1 light guide layer 5
The width W of the portion corresponding to is 25 μm.

Furthermore, as the epitaxial crystal growth method of the example, the MO-CVD method and the MB2 method, which have good thin thickness uniformity, were used, and in addition, the device was manufactured using photolithography technology.

According to this embodiment, the equipolarized refractive index is as follows: Region C (thin portion of the cladding layer 6), Region B (thick portion of the cladding layer 6, without the optical guide layer 5), Region A (light guide layer 5), (parts where layer 5 is provided). If the equipolarized refractive index decreases stepwise from the center of the waveguide toward both ends, the generated light will gather at the center of the waveguide and break up, and filament oscillation can be prevented. .

Further, in the region C, light generated in the active layer 3 slightly seeps into the cap layer 7 and is absorbed. Here, the thickness h of the cladding layer 6 provided under the camp layer 7 is set to 0°4 μm in the above example, but if it is made smaller than this, the light absorption in the region C will increase and the oscillation threshold will be exceeded. while leading to an increase in the value and a decrease in the external differential quantum effect.
When 1° is larger than 0.7 μm, the light passes through the cap layer 7.
, and there is virtually no difference from region B. therefore,
It is preferable that t is 0.4 μm or more and 0.7 μm or less.

Further, in region A, light confinement in the active layer is poor, but by providing the Zn diffusion region 11, it is possible to prevent the gain in region A from decreasing and to create a high carrier injection state. This makes it easier to oscillate in the region A where the peak of the fundamental transverse mode exists, making it easier for the fundamental transverse mode to oscillate in the broad area laser.

The thickness of the optical guide layer 5 is determined by taking into account the difference in refractive index between regions A and B, the cant-off conditions for higher-order modes of the vertical transverse mode, etc. It is desirable that the thickness be 0.4 μm.

Moreover, in this example, GaAj! Although the explanation has been given using an As-based DH laser as an example, the invention is not limited to this, and InG
It can also be applied to semiconductor lasers made of other materials such as aAsPp-based and InGaAsP-based, and semiconductor lasers with quantum well structure and SCH structure.

As described above, according to the present invention, it is possible to obtain an optical output of several hundred to several thousand mW, and it is also possible to control the transverse mode. Therefore, since a high-output laser beam can be focused on a single point using a lens or the like, it is possible to apply the present invention to a wide range of fields such as microfabrication using lasers and optical information processing.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing a broad area laser according to an embodiment of the present invention, and FIG. 2 is a cross-sectional view showing a broad area laser according to an embodiment of the present invention.
A graph showing the refractive index distribution in the n-junction and the horizontal direction, FIG. 3 is a graph showing the absorption loss and gain distribution of the laser of the present invention, and FIG. 4 is a graph showing the transverse mode distribution of the conventional broad area laser. be. 1... Substrate, 2... Clad layer, 3... Active layer,
4... Cladding layer, 5... Light guide layer, 6... Cladding layer, 7... Cap layer, 8... Insulating layer, 9.
10... Electrode, 11... Zn diffusion N region. Figure 1 Figure 2 Position y

Claims (3)

[Claims] (1) A broad area laser with a large waveguide width, characterized in that the equivalent refractive index of the pn junction in the horizontal direction decreases stepwise from the center of the waveguide toward both ends. Broad area laser. (2) In a broad area laser in which a cladding layer is formed on the active layer of the waveguide, about 0.4% from the cladding layer excluding the central part of the waveguide.
A broad area laser characterized in that a semiconductor layer is formed at a position ~0.7 μm above the active layer, the semiconductor layer having a conductivity type that allows current injection into the active layer and having a large absorption coefficient with respect to the oscillation wavelength. (3) A broad area laser having a large waveguide width, characterized in that the amount of carriers injected into the center of the waveguide is larger than the amount of carriers injected into both sides.