JPS59182591A - Photo feedback type semiconductor laser device - Google Patents

Abstract

PURPOSE:To prevent the effect by reflection noises on a laser by contriving to make the vertical mode of the laser single by a method wherein the center of the position of laser oscillation and the center of the position of reflected light are put in proximity without coincidence, in the feedback of the laser emitted light. CONSTITUTION:The emitted light 6 from the active layer 5 of a semiconductor laser chip 1 is made parallel by means of a collimating lens 2, reflected by a reflection optical element 3 such as a mirror and a diffraction grating, turned to a converged light 7 by means of the collimator 2, and then fed back to the resonance end surface 9 of the laser chip 1. The semiconductor laser device is brought to a strong vertical single mode by converging a reflected light region 11 to an oscillation region 10 at this surface 9, and thus putting the luminous center and the reflected light center in arrangement in the neighborhood without coincidence. The emitted light 8 from the other end of the laser chip 1 is introduced to an optical fiber 4 and then made as the light source for optical communication, and accordingly the effect of reflection noises on the laser is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a semiconductor laser device used as a light source for optical communications, optical sensors, various optical sensors, and the like.

Conventional configuration and its problems When using a semiconductor laser as a light source for optical communication, for example, when coupling a semiconductor laser and a fiber, a part of the emitted light from the semiconductor laser returns to the semiconductor laser by reflection from the fiber end face. This is considered to be the cause of instability of the oscillation characteristics of the semiconductor laser and an increase in noise. Therefore, isolators are currently used to prevent the light from returning to the semiconductor laser.

That is, in the field of optical communications, the light returned to the semiconductor laser is considered unnecessary. Furthermore, when considering optical discs as a field of use for semiconductor laser music, it has been pointed out that noise increases when reflected light from the optical disk surface is fed back to the semiconductor laser. However, there is a method that actively uses the returned light as a self-coupling effect, but even with this method, the returned light to the semiconductor laser is unstable, so the oscillation characteristics of the semiconductor laser are also unstable, and the S/N is low. The ratio is poor and has not reached the practical level.

As mentioned above, conventionally, when the laser light emitted from the semiconductor laser returns to the semiconductor laser as return light, it is thought that the oscillation characteristics become unstable and the noise increases, so the return light is effectively controlled. It is not clear how to use it.

Purpose of the Invention The present invention aims to unify a stable longitudinal moat of the semiconductor laser when a part of the emitted light from the semiconductor laser is returned to the semiconductor laser as return light, and to reduce reflection noise to the semiconductor laser. SUMMARY OF THE INVENTION It is an object of the present invention to provide an optical feedback type semiconductor laser which is not affected by the effects of In addition to focusing and returning light, the center of the light emission position of the laser and the center of the position of the reflected light are brought close to each other without having to coincide with each other, thereby unifying the longitudinal mode of the semiconductor laser and suppressing reflection noise due to the reflected reinjected light. In addition, by making the optical path length of the output end of the semiconductor laser and the reflective optical element approximately an integral multiple of the optical path length of the natural resonator of the semiconductor laser, the single-longitudinal mode is stabilized. - To provide a semiconductor laser device that oscillates in a longitudinal mode and oscillates with low noise.

DESCRIPTION OF THE EMBODIMENTS FIG. 1 shows an embodiment 1j of an optical feedback type semiconductor device according to the present invention. Reference numeral 1 indicates a semiconductor laser chip, and schematically represents an active layer 6 within the laser.

The emitted light 6 to the right side of the laser is made parallel by the collimating lens 2, reflected by the reflection optical element 3 such as a mirror 2 diffraction grating, enters the collimating lens 2VC again, becomes a focused light 7, and is focused on the semiconductor laser chip 1. The center of the reflected light is set to be near the emission center of the semiconductor laser tip 1 on the resonator end face 9 .

The positional relationship between the light emission center and the reflected light center on the resonator end face 9 is shown in FIG. FIG. 2 is a drawing of the resonator end face viewed from the direction of the emission of light from the semiconductor laser tip 1, and the resonator end face 9 is normally parallel to the cleavage plane.Light emitting region 1
0 is shown with solid diagonal lines, and the reflected light offshore center 11 is shown with dotted diagonal lines. By converging the reflected light in this manner and arranging the emission center and the reflected light center close to each other without making them coincide, the semiconductor laser exhibits a strong longitudinal single mode property and becomes a laser beam with less noise. Also, so-called reflection noise is suppressed. (Proceedings of the 1967 National Conference of the Institute of Electronics and Communication Engineers, Optical and Radio Division, Proceedings 266, “Reflected light return position dependence of semiconductor lasers”).

Returning to FIG. 1, the emitted light 8 from the other end of the semiconductor device having such a structure can be guided to the optical fiber 4 to be used as an optical communication moonlight source. At this time, considering the oscillation conditions of the semiconductor laser, the oscillation wavelength of the semiconductor laser without a reflective optical element is λ, and the resonator length is λ.

When the refractive index is η, the longitudinal mode spacing △/1 is △λ1;λ
2/ (2n -L) ・Old---(
*). When there is a reflective optical element, if the distance between the resonator end face of the semiconductor laser and the reflective optical element is L', the longitudinal mode interval due to this external resonator is Δno.

is Δpe, -λ/(2L')...
・(2) becomes. This relationship is shown in FIG. Figure 3 shows
When the natural longitudinal mode spacing Δλ1 of the semiconductor laser and the longitudinal mode spacing Δλ2 of the external cavity are very close to each other and the wavelength λ. Indicates the case where both match. The horizontal axis is the wavelength. The solid line shows the eigenmode of the semiconductor laser, and the dotted line shows the external resonance mode. At this time, the semiconductor laser has a wavelength of λ. This results in oscillation with a strong single moat.

The wavelength interval at which these two modes overlap is the least common multiple of ΔA1 and Δλ2, and if Δλ1 and Δλ2 are approximately equal, the wavelength interval at which these two modes overlap becomes narrower. Therefore, the oscillation wavelength of such a semiconductor laser has a very strong single-mode property.0 Also, to achieve this, if the external cavity spacing L' is approximately equal to the effective cavity length (nxL) of the semiconductor laser, then good. Here, the refractive index n of the semiconductor laser is
is about 3 to 4, and the resonator length is 0.2 to 0.4 mm.
Therefore, the external resonator length needs to be about 0.6 to 1.6 cylinders.

A second embodiment of the present invention is shown in FIG. Note that elements common to those in FIG. 1 are given the same number. In this method, a spherical mirror 12 is used as an external reflective optical element. By slightly shifting the output optical axis of the semiconductor laser and the optical axis of this spherical mirror, the reflected light 13 is focused on the resonator end face 9 of the semiconductor laser at a position slightly shifted from the emission center. . In this method, compared to the method using lenses and mirrors mentioned earlier, the mirror and lens are integrated, so
The feature is that the distance from the semiconductor laser to the reflective optical element can be shortened. Also, the radius of this spherical reflective mirror is
Since this system is an imaging system, the optical path length is approximately r, so the variation is approximately 0.3 to 0.7 mm. In addition, in order to correct aberrations, it is preferable to use an aspherical surface rather than a spherical surface, but even a spherical surface poses a major problem (f y u ). It also has the effect of suppressing so-called reflection noise.

In addition, when used as a light source for photonics, the instability of semiconductor laser characteristics due to light reflected from the disk is also reduced.

Effects of the Invention According to the present invention, it is possible to obtain a semiconductor laser device in which strong unity of the semiconductor laser longitudinal mode is stably obtained, there is no reflection noise, and the influence of reflected light is small.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an optical feedback semiconductor laser device according to an embodiment of the present invention, FIG. 2 is a diagram showing a light emitting region and a reflecting region at the end face of the semiconductor laser tenop in FIG. 1, and FIG. 3 is a diagram showing the same as in FIG. 1. FIG. 4 is a diagram showing the configuration of an optical spiral semiconductor laser device according to a different embodiment of the present invention. 1... Semiconductor laser tinop, 2... ... Collimating lens, 3... Reflective optical element, 4...
...Optical fiber, 5...Active layer, 6...
... Outgoing light, 7... Focused light, 8... Outgoing light.

Claims (2)

[Claims] (1) comprising a semiconductor laser and a reflective optical element that focuses and reflects at least a portion of the laser light emitted from the semiconductor laser onto a resonator end face of the semiconductor laser, the center of the light emission position of the semiconductor laser; The center of the position of the reflected light from the reflective optical element is arranged close to each other without coinciding with each other, and the optical path length between the semiconductor laser and the reflective optical element is approximately an integral multiple of the optical path length of the natural resonator of the semiconductor laser. Optical feedback semiconductor laser device. (2) The optical feedback semiconductor laser device according to claim 1, characterized in that a hemispherical reflecting mirror is used as the reflecting optical element.