JPH06310801A - Semiconductor laser - Google Patents

Abstract

PURPOSE:To increase the amount of optical feedback in a mode selected from among five transverse modes than that in the other modes and to make it possible to oscillate a semiconductor laser only in the selected mode by a method wherein a diffraction grating is provided only on a part, in which the intensity of light in the selected mode becomes the largest one, of an optical waveguide. CONSTITUTION:A lateral refractive index waveguide 31 and a diffraction grating 32 for optical feedback are formed by etching a guide layer 13. When the width of the optical waveguide 31, the equivalent refractive index of the waveguide 31 and a difference between the lateral refractive indexes of the waveguide 31 are respectively assumed 10mum, 3.3 and 0.005, five transverse modes ranging from 0 order to a fourth order result in existing in this waveguide. In the case where a semiconductor laser is selectively oscillated in the O-order mode, a light intensity distribution in the O-order mode becomes the largest in the center part of the waveguide. As a result, the grating 32 has only to be formed in the center part of the waveguide. Thereby, the laser can be oscillated only in a mode selected from among the modes and a single-mode semiconductor laser using a wider multimode optical waveguide can be realized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser,
In particular, it relates to a high power single mode semiconductor laser.

[0002]

2. Description of the Related Art The following two problems arise when increasing the output of a semiconductor laser. The end face destruction occurs due to the increase in the light density of the end face of the device. The life of the device is shortened due to the increase of light density and current density inside the device.

In order to solve these problems, it is sufficient to widen the light emitting region and reduce the light density and the current density, and a high power semiconductor laser having a wide optical waveguide width is actually manufactured.

[0004]

However, when the waveguide width is widened, the optical waveguide becomes multimode, so that the semiconductor laser oscillates in multimode especially during high-power operation, and when single mode oscillation is required. It becomes a problem.

The present invention has been made in view of the above problems of the prior art, and a semiconductor laser using a multimode optical waveguide in which the waveguide width is widened by changing the gain required for oscillation in each mode. Also in the above, it is an object to provide a high output single mode semiconductor laser by performing single mode oscillation.

[0006]

The structure of the present invention for solving the above-mentioned problems is a semiconductor laser having a multimode optical waveguide whose refractive index is changed in the lateral direction and utilizing optical feedback by a diffraction grating. In the above, by providing the diffraction grating only in a portion where the light intensity of the selected mode is maximum, the amount of optical feedback of the selected mode is made larger than that of the other modes, and oscillation is performed only in the selected mode. It is characterized by

[0007]

According to the present invention, even in a semiconductor laser using a multimode optical waveguide having a wide waveguide width, by providing a diffraction grating only in a portion where the light intensity of the selected mode is maximum, Can only be oscillated by.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings. FIG. 1 is a perspective sectional configuration view showing a semiconductor layer structure, which is an example of a semiconductor laser of the present invention and is a single quantum well distributed feedback laser. In FIG. 1, the semiconductor layer structure is
From the upper side, 11: p-type GaAs cap layer [0.3 μm] 12: p-type Al _0.6 Ga _0.4 As clad layer [1.5 μ
m] 13: p-type Al _0.3 Ga _0.7 As guide layer [30 nm] 14: p-type Al _0.6 Ga _0.4 As carrier block layer [20 nm] 15: undoped Al _X Ga _1-X As (X = 0.6-
0.3) GRIN (graded index) layer [150 nm] 16: undoped GaAs quantum well layer [10 nm] 17: undoped Al _X Ga _1-X As (X = 0.3-)
0.6) GRIN layer [150 nm] 18: n-type Al _0.6 Ga _0.4 As clad layer [1.5 μ
m] 19: n-type GaAs buffer layer [0.5 μm] 20: n-type GaAs substrate.

Further, in FIG. 1, 21: SiO ₂ and 2
2: The ridge structure is provided to limit the current injection region.

Next, FIG. 2 shows an etching shape of the guide layer 13 of FIG. In FIG. 2, the refractive index waveguide 31 in the lateral direction and the diffraction grating 32 for optical feedback are shown in FIG.
Is formed by etching.

In such a structure, assuming that the width of the optical waveguide 31 is 10 μm, the equivalent refractive index is 3.3, and the lateral refractive index difference is 0.005, this waveguide has 0th to 4th order. There will be five transverse modes. The light intensity distribution of these modes is shown in FIG. When the 0th-order mode is selectively oscillated, the light intensity distribution of the 0th-order mode shown in FIG. 3 (a) becomes maximum in the central part of the waveguide, so that as shown in FIG. A lattice may be formed. Here, Table 1 shows the ratio of the coupling coefficient of the diffraction grating of each mode when the width of the diffraction grating formed in the central portion is 4 μm.

[0012]

As shown in Table 1, the structure of FIG.
The coupling coefficient of the next mode can be maximized. As a result, the amount of optical feedback in the 0th-order mode becomes larger than that in the other modes, the oscillation threshold gain in the 0th-order mode decreases, and single-mode oscillation occurs in the 0th-order mode.

Next, when a mode other than the 0th-order mode is selected, similarly, a diffraction grating is formed in a portion where the light intensity distribution of each mode is maximum. For example, when the primary mode is selected, the light intensity distribution in the primary mode shown in FIG.
A diffraction grating may be formed in one part. Each diffraction grating width is 2 μm (the total diffraction grating width is 4 μm because there are two locations)
Table 2 shows the ratio of the coupling coefficient of the diffraction grating for each mode when
Shown in.

[0015]

As shown in Table 2, the coupling coefficient of the first mode can be maximized. As a result, the amount of optical feedback in the first-order mode becomes larger than that in the other modes, the oscillation threshold gain of the first-order mode decreases, and single-mode oscillation occurs in the first-order mode.

Similarly, single mode oscillation is possible even in the second to fourth modes.

Although the distributed feedback laser has been described in the above embodiment, other semiconductor lasers using optical feedback by a diffraction grating such as a distributed reflection laser can be used.

Conventionally, in the case of increasing the output of a semiconductor laser, the optical waveguide width is widened in order to reduce the light density and the current density. In this case, however, a single mode oscillation is obtained because the optical waveguide becomes a multimode optical waveguide. It will be difficult. Therefore, when single mode oscillation is required, the waveguide width cannot be widened, which limits the maximum output.

According to the present invention, even in a semiconductor laser using a multimode optical waveguide having a wide waveguide width, by providing a diffraction grating only in a portion where the light intensity of the selected mode is maximum, only in the selected mode. Can be oscillated. Therefore, a single-mode semiconductor laser using a wider multimode optical waveguide can be realized, and an effect of increasing the output of the single-mode semiconductor laser can be particularly expected.

[0021]

As described above in detail with reference to the embodiments, according to the present invention, even in a semiconductor laser using a multimode optical waveguide having a wide waveguide width, the light intensity of the selected mode is maximum. By providing the diffraction grating only in the portion to be formed, a semiconductor laser capable of oscillating only in the selected mode can be realized.

[Brief description of drawings]

FIG. 1 is a perspective cross-sectional configuration diagram showing a semiconductor layer structure, which is an example of a semiconductor laser of the present invention and exemplifies a single quantum well distributed feedback laser.

FIG. 2 is a diagram showing an etching shape of a guide layer of FIG.

FIG. 3 is a diagram showing a light intensity distribution of each transverse mode.

[Explanation of symbols]

 13 Guide layer 31 Refractive index waveguide 32 Diffraction grating

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Michio Dobashi 2-9-32 Nakamachi, Musashino-shi, Tokyo Yokogawa Electric Co., Ltd.

Claims (1)

[Claims] 1. In a semiconductor laser having a multimode optical waveguide whose refractive index is changed in the lateral direction and utilizing optical feedback by a diffraction grating, the diffraction is performed only in a portion where the light intensity of the selected mode is maximum. A semiconductor laser characterized in that by providing a grating, the amount of optical feedback in the selected mode is made larger than that in other modes, and oscillation is performed only in the selected mode.