JPS63318790A - Semiconductor laser array - Google Patents

Abstract

PURPOSE:To obtain a semiconductor laser array emitting a single beam from an end surface by a method wherein a plurality of laser resonators are arranged in a relation of position where a discontinuous phase of pi/2 is produced to the cycle of the arrangement near the center of that arrangement. CONSTITUTION:Plural number of laser resonators, which are arranged parallel and cyclically and oscillate with internal light interfering each other, are provided on the same semiconductor substrate. In such semiconductor laser array, plural laser resonators are arranged in a relation where phase discontinuity of pi/2 is produced to the cycle of the arrangement near the center of the arrangement. For example, a long and slender section with a cycle of A and parallel is provided on an n-type clad layer 1 out of a layer structure made by an n-type clad layer 1, an active layer 2, and a p-type clad layer 3, and the width of the discontinuous projecting section is made 1/4 of the cycle, that is, phase of pi/2. Thus, when the width of the projecting section and the gap of the projecting section are the equal, the width of the projecting section at the middle of the arrangement or the gap between the projecting sections is made 1.5 times.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a semiconductor laser light source with high output and sharp directivity. INDUSTRIAL APPLICABILITY The present invention is suitable for use as a light source for optical communication, optical storage and reproduction, optical calculation, and other applications.

[Conventional technology]

Semiconductor lasers are small, lightweight, highly reliable, and can be easily oscillated by current injection.
It has already been used in the field of optical transmission and the storage and reproduction of information using optical disks. However, in order to expand the scope of application to longer distance optical transmission, writable optical disks, and other fields, It is necessary to improve the output power, which is currently about 10 mV, by more than an order of magnitude.In order to obtain such a high output power, it is necessary to arrange a large number of semiconductor lasers in parallel and periodically, and to A phase-locked semiconductor laser array has been proposed in which the laser beams are mutually coupled to generate oscillation. By using such a semiconductor laser array, a high output optical output with sharp directivity can be obtained.

FIG. 4 shows a perspective view of a first conventional semiconductor laser array. This semiconductor laser array is called a refractive index modulation type.

This semiconductor laser array has a layered structure including an n-type cladding layer 1, an active layer 2, and an n-type cladding layer 3. n
The mold cladding layer 3 is provided with parallel and periodically elongated convex portions. Here, for convenience of explanation, the direction in which the convex portions are arranged is referred to as the X direction, the direction in which the layered structure is formed is referred to as the X direction, and the length direction of the convex portions is referred to as two directions.

FIG. 5 shows the refractive index period of this semiconductor laser array.

The convex portion provided in the n-type cladding layer 3 changes the refractive index of a region in the vicinity thereof, spatially modulating the refractive index in a direction perpendicular to the optical axis, that is, in the X direction. This refractive index change defines the light emitting region in the active layer 2 and defines the individual laser resonators.

In addition, the arrangement of the convex portions allows the light propagating through each region to
A plurality of laser resonators are set to oscillate in synchronization by interfering with each other in the directions.

When this semiconductor laser array is operated, each laser resonator oscillates in synchronization with each other and outputs light in two directions. At this time, since the phases of the emitted light from each laser resonator match, the emitted light from the semiconductor laser array exhibits sharp directivity.

FIG. 6 shows the end face structure of a second conventional semiconductor laser array. In addition to the refractive index modulation type described above, a gain modulation type is known as a distributed feedback type semiconductor laser array. The conventional example shown in FIG. 6 is a gain modulation type semiconductor laser array.

A gain modulation type semiconductor laser array has an n-type cladding layer 1
, is similar to the refractive index modulation type in that it has a layer structure consisting of an active layer 2 and an n-type cladding layer 3, but the n-type cladding layer 1
On the surface of the electrode 6, instead of convex portions, electrodes 6 are arranged at regular intervals and in parallel. By injecting a bias current from this electrode 6 into the active layer 2 formed on the negative plane, the gain is modulated. Therefore, the light emitting region 4 is defined by the electrode 6 .

In the case of the gain modulation type as well, the far field pattern becomes bimodal as in the refractive index modulation type.

FIG. 7 shows a far-field image of a conventional refractive index modulated semiconductor laser array.

A phase-locked semiconductor laser array generally exhibits a bimodal far-field pattern. There are several theoretical interpretations, one of which is the theory of a laterally distributed feedback semiconductor laser by Suemne et al. of the Faculty of Engineering, Hiroshima University. This theory is described in Room Temperature Operation of a Transverse Distributed Feedback Cavity Laser, Electronics Letters, Vol. 18, 1982, p. 745 ('Room
Tempera-ture operation of
a transverse-distributed
-feedback cavity 1aser”,
Electronics Letters.

Vol, 18.1982. p, 745). According to this theory, if the spatial period of the laser resonator is A1 and the wavelength in vacuum of the light oscillated within this laser resonator is A, then the angle θ of the emitted beam is For lines, that is, two directions, it is given by θ=±5in-' (λ/2A). In this direction, a component of the wave number vector of light propagating in the laser resonator in a direction perpendicular to the optical axis satisfies the Bragg condition due to the periodic refractive index distribution.

[Problem that the invention seeks to solve]

An object of the present invention is to provide a semiconductor laser array that emits a single beam from an end face.

[Means for solving problems]

The semiconductor laser array of the present invention is a semiconductor laser array including a plurality of laser resonators arranged in parallel and periodically on the same semiconductor substrate and whose internal light interferes with each other to oscillate. is characterized by being arranged in a positional relationship such that a phase discontinuity of approximately π/2 occurs in the period of the array near the center of the array.

[For production]

The theory of Suemne et al. described above is equivalent to the theory for the oscillation spectrum of a normal distributed feedback semiconductor laser in which the refractive index has periodicity in the optical axis direction.

The difference is whether it appears as a spatial spectrum or a temporal spectrum.

It is known that the spectrum of a typical distributed feedback semiconductor laser becomes bimodal when reflection from the laser cavity end face can be ignored. In order to make such an oscillation spectrum unimodal, a method of making the phase of periodic modulation of the refractive index discontinuous has been proposed, and an actual device has been prototyped.

For example, Utaka et al. of KDD Research Institute, ``Study of oscillation characteristics of DFB laser with λ/4 shift grating'',
At the IEICE General Conference 1017 in 1981, a distributed feedback semiconductor laser in which the phase of the diffraction grating is antisymmetrical and shifted by an amount equivalent to 1/4 of the tube wavelength near the center of the DFB region was discovered to have a Bragg wavelength. It is explained that oscillation occurs only when Then, such a λ/4 shift DFB
Lasers are already at a stage where they can be put into practical use.

On the other hand, the present invention applies a method of unifying the oscillation spectrum by matching it to the Bragg wavelength due to the equipolarization of the spatial spectrum and the temporal spectrum. This will give you a uniform beam.

〔Example〕

FIG. 1 shows a perspective view of a semiconductor laser array according to a first embodiment of the present invention, and FIG. 2 shows an output end face.

This semiconductor laser array has a layered structure including an n-type rad layer 1, an active layer 2, and an n-type cladding layer 3, as in the conventional example. The n-type cladding layer 3 is provided with elongated parallel convex portions with a period Δ, but the difference from the conventional example is that the periodicity of the convex portions is discontinuous at the center. Although the electrode is not shown, it is a front electrode.

The width of the discontinuity of the convex portion is 174 to its period, i.e. π
/2 phase. When the width of the protrusions and the interval between the protrusions are equal, the width of the protrusion at the center of the array or the interval between the protrusions is set to 1.
Multiply by 5.

Here, for the sake of explanation, a coordinate system similar to that of the conventional example will be used. That is, the direction in which the convex portions are arranged is the X direction, the direction in which the layered structure is formed is the X direction, and the length direction of the convex portions is the two directions.

The convex portion provided in the n-type cladding layer 3 changes the refractive index of a region in the vicinity thereof, spatially modulating the refractive index in a direction perpendicular to the optical axis, that is, in the X direction. This refractive index change defines the light emitting region 4 in the active layer 2 and defines the individual laser resonators.

In addition, the arrangement of the convex portions allows the light propagating through each region to
A plurality of laser resonators are set to oscillate in synchronization by interfering with each other in the directions.

Each laser resonator oscillates in synchronization with each other and outputs light from the light emitting region 4 in two directions. Since the phases of the emitted light from each laser resonator match with each other, the emitted light from the semiconductor laser array exhibits sharp directivity. At this time, since the periodicity of the laser resonator has a phase shift of π/2 at the center, unimodal output light is obtained.

When controlling the oscillation spectrum of a typical distributed feedback semiconductor laser, it is necessary to consider reflected light from the laser end facet. However, in the case of a laser array, the light emitting region 4
There is no need to consider reflected light because light is absorbed outside the .

FIG. 3 shows an end face of a semiconductor laser device according to a second embodiment of the present invention. In this embodiment, the present invention is implemented using a quantum well type semiconductor laser array.

This semiconductor laser array has a layered structure consisting of an n-type cladding layer 1, an active layer 2' having a quantum well structure, and an n-type cladding layer 3, which is disordered by impurity diffusion to define a light emitting region 4. A region 5 is provided. The disordered region 5 is formed such that the period of the arrangement of the light emitting regions 4 is shifted by 174 of the period A at the center of the arrangement, that is, the phase is shifted by π/2.

In this embodiment, the widths of the light emitting regions 4 and the intervals therebetween (the widths of the disordered regions 50) are equal, and the width of the central light emitting region 4' is 1.5 times the width of the other light emitting regions. The present invention can be similarly practiced even when the widths of the light-emitting regions 4 and the intervals therebetween are different, and the present invention can be similarly practiced even when the intervals between the light-emitting regions 4 are widened instead of the width of the light-emitting regions 4'.

The present invention can be applied to a gain modulation type semiconductor laser array, but since loss occurs between the light emitting regions 4, it is difficult to control the beam shape.

In the above embodiments, an example in which the convex portions or disordered regions 5 are provided in the n-type rad layer l has been described on the premise that an n-type substrate is used. It can be implemented similarly.

〔Effect of the invention〕

As explained above, the semiconductor laser array of the present invention has
It can emit a single output beam at high power. The semiconductor laser array of the present invention has optical communication including air propagation,
In addition to writing on optical disks or magneto-optical disks, the present invention can be used as a light source device for optical processing devices, a laser scalpel for shaping, a light source for laser display, and so on.

[Brief explanation of drawings]

FIG. 1 is a perspective view of a semiconductor laser array according to a first embodiment of the present invention. Figure 2 is a structural diagram of the end face. FIG. 3 is a structural diagram of an end face of a semiconductor laser array according to a second embodiment of the present invention. FIG. 4 is a perspective view of a first conventional semiconductor laser array. FIG. 5 is a diagram showing the refractive index distribution. FIG. 6 is a structural diagram of an end face of a second conventional semiconductor laser array. FIG. 7 is a diagram showing a far-field image of a conventional refractive index modulated semiconductor laser array. 1...n-type cladding layer, 2.2'...active layer, 3.
...p-type cladding layer, 4.4'...light emitting region, 5...
- Disordered region, 6... electrode. Patent Applicant Nippon Telegraph and Telephone Corporation 7/~ Agent Patent Attorney Takashi Ide 1 Figure 1 Embodiment ←^Chi^shi-A→-→・ 2 Figure 1 End face of the 1st embodiment
Figure 3 End face of the second embodiment Figure 4 Conventional example Figure 5 Refractive index distribution Figure 6 Conventional example

Claims (1)

[Claims] (1) In a semiconductor laser array comprising a plurality of laser resonators that are arranged in parallel and periodically on the same semiconductor substrate and emit light by interfering with each other, the laser resonators are A semiconductor laser array characterized in that the semiconductor laser array is arranged in a positional relationship that causes a phase discontinuity of approximately π/2 in the period of the array near the center.