JPS61240691A - Light source - Google Patents

Abstract

PURPOSE:To enable the oscillation mode of a semiconductor laser to be stably changed from the single vertical mode to the multiple mode, by returning a part of light beams emitted from the semiconductor laser to the light-emitting face of the semiconductor laser by means of a partially reflecting mirror. CONSTITUTION:In the present light source employing a semiconductor laser, a partially reflecting mirror 13 having a flat plate shape is arranged at a predetermined angle such that a part of light beams from a lens 1 is transmitted by the mirror while the other part of the light beams is returned thereby to the lens 12 along a path parallel with the original light path. Further, the amount of light collected by the lens 12 and returned to the light-emitting end face of the semiconductor laser chip 10 is set so as to be sufficient to change the oscillation mode from the single vertical oscillation mode to the stable multiple mode. Light beams emitted from the light- emitting end face of the semiconductor laser chip 10 oscillating in the single vertical mode are converted into parallel beams by the lens 12 and applied to the partially reflecting mirror 13. The light beams reflected from the mirror 13 are collected by the lens 12 and returned to the light-emitting end face of the semiconductor laser chip 10, whereby the oscillating operation of the semiconductor laser chip 10 is stably changed to the multiple mode.

Description

[Detailed Description of the Invention] [Summary] The present invention provides a light source using a semiconductor laser with a simple structure and a simple structure by returning a part of the emitted light from the semiconductor laser to the light emitting end facet of the semiconductor laser using a partial reflecting mirror. This is a stable multi-mode version of a semiconductor laser that oscillates in a single longitudinal mode.

[Industrial application field]

The present invention relates to a light source using a semiconductor laser, and particularly to a light source that performs stable multimode oscillation.

In general, light generated by single longitudinal mode oscillation has noise due to mode hopping, and the coherence of the light source is good, so in an interference needle such as an optical fiber gyro that propagates light from the same light source in opposite directions, the end face of the optical component is used. Reflected light and backscattered light in the fiber interfere with the signal light and become noise.

Therefore, when such a problem arises, multi-mode light is conventionally used.

[Conventional technology]

Conventionally, as a light source for obtaining multi-mode light, ■ a light source that modulates a semiconductor laser that performs single longitudinal mode oscillation at high frequency (for example, 1983, Fall, Proceedings of the 44th Japan Society of Applied Physics Academic Conference, 26a- (See page 6, ``Low noise and longitudinal mode characteristics of semiconductor lasers by high-frequency superposition'') ■A light source using a superluminescent diode is known.

[Problem that the invention seeks to solve]

However, the light source of ■ is an oscillator for superimposing high frequencies,
This has the disadvantage that the modulator becomes a major loss and the light source itself becomes larger.

Furthermore, the light source (2) is basically unstable and has problems in manufacturing yield, reliability, etc.

An object of the present invention is to use a semiconductor laser that performs normal single-dark blue mode oscillation and to perform stable multi-mode oscillation by simply adding simple parts.

[Means for solving problems]

In order to achieve the above object, the present invention has a structure in which light emitted from a semiconductor laser is extracted to the outside through a partial reflection mirror, and the amount of light reflected by the partial reflection mirror and returned to the light emitting end face of the semiconductor laser is The oscillation mode of the semiconductor laser is set to an amount that changes the oscillation mode from a single longitudinal mode to a stable multimode.

In a preferred embodiment of the present invention, the reflecting surface of the partially reflecting mirror is a flat surface, and the emitted light from the light emitting end face of the semiconductor laser is collimated between the semiconductor laser and the partially reflecting mirror. A lens is disposed to send light to the partially reflecting mirror.

[Focus of the invention]

As part of the development and research of the optical fiber gyro, the present inventor investigated the influence of return light from a semiconductor laser using a measurement system as shown in FIG. 2, for example.

In FIG. 2, 1 is a semiconductor laser that performs single longitudinal mode oscillation, and its emitted light is converted into parallel light by a lens 2.
The light is incident on the half mirror 3. The light incident on the half mirror 3 passes through the half mirror 3 and enters the optical fiber 5 through the lens, and is partially reflected by the half mirror 3 and enters the reflecting plate 6.

Further, the light incident on the reflection plate 6 enters the half mirror 3 through the same optical path as the original light, and the light reflected by the half mirror 3 is converged by the lens 2 and returns to the light emitting end face of the semiconductor laser 1. It is configured.

The light incident on the optical fiber 5 is taken into the optical spectrum analyzer 7, where the spectrum is measured.

The measured spectrum is then recorded on paper by an X-y recorder 8 connected to the analyzer 7.

In the measurement system shown in FIG. 2, the inventor first measured the spectrum using a glass plate with low reflectance as the reflector 6, and a spectrum indicating multimode was observed. It was confirmed that it constantly changes and is not stable. FIGS. 3(a) to 3(d) show different spectra observed at that time.

Next, when the spectrum was measured using a total reflection mirror as the reflection plate 6, a spectrum indicating multimode as shown in FIG. 4, for example, was observed, and the spectrum remained constant during the measurement.

There is no doubt that such a difference in results is due to a difference in the reflectance of the reflecting plate 6, and in turn, due to the amount of light returning to the semiconductor laser.

Therefore, the inventor continued to observe the spectrum while changing the reflectance of the reflector 6, and found that the spectrum indicating multimode becomes stable when the reflectance of the reflector 6 exceeds a certain value. It was confirmed.

The present invention has been made with attention to these points,
Examples will be described below.

〔Example〕

FIG. 1 is an explanatory diagram of the configuration of an embodiment of the present invention, in which 10 is a semiconductor laser chip that performs single longitudinal mode oscillation;
Fixed on 1. A lens 12 that converts the light emitted from the semiconductor laser chip 10 into parallel light is disposed in front of the light emitting end face of the semiconductor laser chip 10.
A partial reflecting mirror 13 that reflects part of the light is disposed on the opposite side of the second semiconductor laser chip 11.

In this embodiment, the partial reflecting mirror 13 has a flat plate shape, and is mounted at a predetermined angle so that it transmits the light from the lens 12 and partially reflects it back to the lens 12 in parallel with the original optical path. ing. In addition, the reflectance of the partial reflecting mirror 13 is such that the amount of light that is reflected by the mirror, converged by the lens 12, and returned to the light emitting end face of the semiconductor laser chip 10 changes the oscillation mode from a single longitudinal mode to a stable multi-mode. The amount is set to be sufficient for Since such a lower limit value of reflectance differs between the two types of semiconductor lasers, it is desirable to set it for each semiconductor laser.

In particular, the light taken out from the partial reflecting mirror 13
The reflectance of the partial reflecting mirror 13 is adjusted so that the semiconductor laser chip 10 stably becomes multi-mode when the partial reflecting mirror 13 does not return to the normal state, that is, when there is nothing on the opposite side of the partial reflecting mirror 13 from the lens 12. If you set , partial reflector 1
It is not affected by reflection at the end face of the lens or optical fiber that occurs when the light from 3'#- is guided to the optical fiber via a lens or the like.

Since this embodiment has the above-described configuration, the light emitted from the light emitting end face of the semiconductor laser chip 10 is converted into parallel light by the lens 12 and enters the partial reflection mirror 13, and the light reflected by the partial reflection mirror 13 is The light is focused by the lens 12 and returned to the light emitting end face of the semiconductor laser chip 10, and the oscillation of the semiconductor laser chip 10 is stabilized and made multi-mode. In addition,
The light transmitted through the partially reflecting mirror 13 is used as the output light of the light source.

In the above embodiment, the lens 12 is provided between the semiconductor laser chip 10 and the partial reflection mirror I3, but this is done by reducing the reflectance of the partial reflection mirror 13 as much as possible to increase the output light and to ensure sufficient return light. The lens 12 can be omitted in a system in which a reduction in output light is allowed.

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to use a semiconductor laser that performs normal single longitudinal mode oscillation and to perform stable multi-mode oscillation by simply adding a simple component such as a partial reflecting mirror. I can do it.

[Brief explanation of drawings]

Figure 1 is a configuration diagram of an embodiment of the present invention, Figure 2 is a configuration diagram of a measurement system used to examine the influence of return light from a semiconductor laser, and Figure 3 is a reflection plate in the measurement system of Figure 2. Figure 4 is a diagram showing the different states of the spectrum obtained when a glass plate with a low reflectance is used as the reflectance plate 6. FIG. 3 is a diagram showing the state of the obtained spectrum.

Claims (2)

[Claims] (1) It has a structure in which the emitted light from the semiconductor laser is extracted to the outside via a partial reflection mirror, and the amount of light reflected by the partial reflection mirror and returned to the light emitting end facet of the semiconductor laser is determined by the oscillation of the semiconductor laser. A light source characterized in that the amount is set to change the mode from a single longitudinal mode to a stable multimode. (2) In the light source according to claim 1, the reflecting surface of the partially reflecting mirror is a flat surface, and the light emitted from the light emitting end face of the semiconductor laser is disposed between the semiconductor laser and the partially reflecting mirror. A light source comprising a lens that collimates the light and sends the parallelized light to the partial reflecting mirror.