JPS6043679B2 - Semiconductor laser device with coupling circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a semiconductor light emitting device, and more particularly to a semiconductor laser that includes a coupling circuit that facilitates coupling to another light emitting device and further oscillates in a single axis mode.

Semiconductor lasers are expected to be one of the main light sources for optical fiber communications and optical information processing, which have been rapidly developed recently, and efforts are being made to improve their performance, but there are still many deficiencies. . One of them is the problem of oscillation spectrum. That is, in optical information processing using large-capacity, long-distance optical fiber communication, holography, etc., it is desirable that the spectrum of the light source consists of a single wavelength. This is because if the spectrum of the light source contains many wavelength components, when the light propagates over long distances in an optical fiber, the arrival time will differ due to the difference in the refractive index of the optical fiber material for each wavelength. This is because wavelength distortion due to so-called wavelength dispersion (or material dispersion) increases. On the other hand, in holography, the broadening of the spectrum of the light source blurs the output image and degrades the signal-to-noise ratio of the output. In contrast, the oscillation spectrum of conventional semiconductor lasers often consists of several to ten axial modes. Some semiconductor lasers have been developed that emit single-axis mode oscillation when excited with a constant current due to improvements in the stripe structure. It was inevitable that the number of carriers would change to a multi-axis mode. Up to now, as one method for realizing a single-axis mode in a semiconductor laser, a method has been devised in which at least one of the resonator reflectors of the semiconductor laser is replaced with a diffraction grating.

This structure is extremely effective in obtaining single-axis mode oscillation, but because it employs a so-called external resonator structure, it is somewhat less stable than a resonator that uses normal crystal cleavage. Ta. Furthermore, since the emitted beam of a semiconductor laser often has a large divergence angle, it is necessary to use a coupling circuit consisting of an appropriate optical system in order to couple it to another optical system. In conventional semiconductor lasers that obtain single-axis mode oscillation, both the external mirror of the diffraction grating and the coupling circuit must be installed close to the semiconductor laser element, resulting in a complex structure and a large number of components. There were a lot of problems, and manufacturing was somewhat difficult.

An object of the present invention is to provide a single-axis mode oscillation device with a coupling circuit that is simple in structure, easy to manufacture, and stable.

According to the present invention, the semiconductor laser element is installed close to the output end face of at least one of the semiconductor laser elements, has a refractive index that gradually decreases from the center to the periphery in a plane perpendicular to the central axis, and has an internal structure. A single-axis mode oscillation semiconductor laser device with a coupling circuit including a focusing optical transmission body having a diffraction grating is obtained.

The principle of this invention is based on the following fact experimentally discovered by the inventors of this invention.

That is, the oscillation spectrum of a semiconductor laser changes in response to the light emitted from the laser itself. Therefore, if only a small portion of the light emitted from a semiconductor laser is returned to the semiconductor laser using an optical element with wavelength selectivity, the oscillation spectrum can be narrowed. In other words, the semiconductor laser itself is oscillated by a stable resonator made by, for example, cleavage, and by partially feeding back the emitted light to it using a diffraction grating, etc., the oscillation spectrum is made into a single-axis mode. be able to. By doing so, stability can be improved compared to a conventional single-axis mode oscillation semiconductor laser in which a diffraction grating is provided externally as one of the resonator reflectors. Furthermore, in this invention, the diffraction grating is formed integrally with the coupling circuit made of the speed-concentrating light transmitter whose refractive index gradually decreases from the center to the periphery. Compared to conventional devices in which both feedback circuits for uniaxial mode are installed separately, the number of parts is small, the structure is simple, and manufacturing is easy. Please refer to the drawings below. A detailed description of the invention will be given below. FIG. 1 is a perspective view of a first embodiment of the invention, and FIG. 2 is a sectional view thereof.

A'GaAs-GaAs-AeGa made by the usual well-known liquid phase growth method and with a cavity formed by cleavage.
A semiconductor laser element 1 having an As double heterostructure is fixed to a heat sink 2 by metal fusion. The speed-concentrating optical transmitter 3 installed close to one cavity end face 20 of the semiconductor laser device 1 is provided with a refractive index distribution that gradually decreases from the central axis 30 toward the periphery. Its central axis 3
A diffraction grating 10 is formed approximately at the center in the 0 direction, making an angle of 70 degrees with the central axis 30. In this example,
A convergent light transmitter 3 is manufactured by imparting the above-mentioned refractive index distribution to a glass round rod using the ion exchange method, and a plastic film is applied to the surface polished at 70 degrees with respect to the central axis 30. After forming a periodic structure by a method combining laser beam interference and etching, a dielectric film with a reflectance of about 20% was deposited to form the diffraction grating 10, and another light-collecting light beam fabricated in the same manner. The transmission body was glued. The length of the convergent light transmitter 3 in the direction of the central axis 30 was selected to be approximately 1/2 of the meandering pitch of the light beam incident from one end surface with an axis offset. By doing this, a real image of the object on one end surface is formed on the other end surface, as is well known as the light beam conversion effect of a condensing light transmission body. That is, in this embodiment, by bringing the incident end face 21 of the converging light transmitting member 3 close to one resonator end face 20 of the semiconductor laser element 1, the output end face 22 of the equivalent converging light transmitting member 3 is A resonator end face 20 is formed at the position. Therefore, by placing the end of the optical fiber 5 close thereto, the light beam 40 emitted from the semiconductor laser element 1 can be efficiently coupled to the optical fiber 5. At this time, a specific wavelength component of the emitted light beam 40 is fed back to the semiconductor laser device 1 by the diffraction grating 10, and the axial mode is unified by the wavelength-selective optical feedback. In other words, the focusing optical transmission body 3 having the diffraction grating 10 inside functions not only as a coupling circuit to the optical fiber but also as a feedback circuit for creating a single-axis mode at the same time. Compared to other devices, the number of parts was small, the structure was simple, and manufacturing was relatively easy. Moreover, since the resonator of the semiconductor laser element 1 is made of a stable material such as a crystal cleavage plane,
It was more stable than conventional devices using external resonators.
FIG. 3 shows a sectional view of a second embodiment of the invention.

A convergent optical transmitter 3'' having a diffraction grating 10 inside is installed close to one resonator end face 20 of the semiconductor laser element 1 fixed to the heat sink 2, and is further placed close to the output end face 22 of the convergent optical transmitter 3'' to transmit light. The end of the fiber 5 is installed.In this embodiment, the diffraction grating 1' is formed in a plane substantially perpendicular to the central axis 3' of the focusing optical transmission body 3', and the semiconductor laser element 1 and the optical fiber 5 to its central axis 3'
It was installed in a position shifted from the The method of manufacturing the convergent optical transmitter 3'' and the diffraction grating 1'' is as described in the first embodiment.The semiconductor laser element 1 is aligned with respect to the central axis 30'' of the convergent optical transmitter 3'' By staggered installation, it was possible to make the emitted light beam 4' enter the diffraction grating 1' at an appropriate angle, and by returning only the light of the desired wavelength, it was possible to unify the axial mode. Furthermore, since the light beam 4' meandered through the convergent light transmission body 3', the light that passed through the diffraction grating 1' could be coupled to the optical fiber 5, which was installed with its axis shifted. In this embodiment, since the surface forming the diffraction grating 1' is almost perpendicular to the central axis 3', it is easier to polish the surface of the convergent light transmitter and fabricate the diffraction grating than in the first embodiment. It was hot. This invention can be modified in several ways in addition to the basic embodiment described above.

First, in the embodiment, the length of the convergent optical transmission bodies 3, 3'' was selected to be approximately 1/2 of the meandering pitch, but it is not limited to this. In other words, this length is a half-integer multiple of the meandering pitch. Almost the same effect as described in the embodiment can be achieved even by using a convergent optical transmission body with an additional length.
Focusing light conduits with lengths shorter than /2 can also be used. In that case, it is necessary to provide an appropriate distance between the semiconductor laser element 1 and the optical fiber 5. Of course, a transparent material may be inserted into this gap. In addition, in the embodiment, materials with almost the same characteristics were used as the focusing optical transmission materials sandwiching the diffraction gratings 10 and 1', but they do not have to be the same, and for example, the degree of change in the refractive index distribution Two speed-concentrating optical transmission bodies with different speeds may be used. By doing so, the emitted beam diameter of the semiconductor laser muncture 1 can be appropriately converted, and the beam can be coupled to the optical fiber 5 more efficiently. The position of the diffraction gratings 10, 1' is not limited to the longitudinal center of the converging light transmitter, but it is preferable to place it at a portion of the convergent light transmitter where the diameter of the light beam is large and the beams are almost parallel. . By doing so, the diffraction grating 1
0,1' is sufficiently reflected, and the diffraction grating 10
, 1', the influence of partial defects etc. is reduced. Further, in the embodiment, a focusing optical transmission body 3 including a diffraction grating 10, 1',
3'' was used as a coupling circuit to the optical fiber 5, but it is also possible to install other optical elements, such as a photodetector, at the position of this optical fiber 5 and use it as a coupling circuit to those optical elements. Needless to say, it can be done.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of a first embodiment of the invention, FIG. 2 is a sectional view thereof, and FIG. 3 is a sectional view of a second embodiment of the invention. In the figure, 1 is a semiconductor laser element, 2 is a heat sink, 3, 3'' is a speed-concentrating optical transmission body, 5 is an optical fiber, 1
0 and 1' are the diffraction gratings, 20 is the end face of the semiconductor laser element 1, 21 and 22 are the end faces of the convergent optical transmission body 3, 30 and 3' are the central axes, and 40 and 4' are the light beams, respectively. .

Claims (1)

[Claims] 1. A semiconductor laser element, which is installed close to at least one of its output end faces, has an entrance/exit end face substantially perpendicular to the central axis, and has a refractive index gradually increasing from the center toward the periphery in a plane perpendicular to the central axis. 1. A semiconductor laser device with a coupling circuit, comprising: a converging light transmitting member having a decreasing velocity; and a diffraction grating disposed inside the converging light transmitting member in a plane crossing the central axis.