JPH01181590A - Semiconductor laser module with external resonator - Google Patents

Abstract

PURPOSE:To prevent a feedback light beam from being angularly displaced by arranging a prism on an optical path of a collimated light beam so that an optical transmission surface faces a lens and a reflecting plate. CONSTITUTION:A prism 10 is arranged on an optical path of a collimated light beam in a manner that an optical transmission surface faces a lens 2 and a reflecting plate 5. A light emanating from one end surface of a semiconductor laser 1 is converted by the lens 2 into a collimated light beam which enters the prism 10. The incident light is reflected on a reflecting surface of the prism 10 and emanates from the prism 10. While, the collimated light beam from the lens 2 propagates back and reaches a reflecting plate 3. The light beam reaching the reflecting plate 3 is reflected thereon, and propagates through the same optical path of the light which reaches the reflecting plate 3 through the lens 2 and the prism 10, i.e., recoupled with the semiconductor laser 1 through the prism 2 and the lens 10. Hereby, the feedback light beam is prevented from angularly displaced even when there is produced any angular displacement.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a semiconductor laser module with an external resonator, and particularly relates to an improvement in the external resonator structure.

(Prior Art) Conventionally, as a semiconductor laser module equipped with an external resonator, for example, "A Study on Narrowing the Spectral Linewidth and Frequency Stabilization of an External Cavity Semiconductor Laser," Telecommunications Research Group, 0QE85- 173. 2 is a configuration diagram showing a semiconductor laser device to which a conventional semiconductor laser module is applied. In the figure, 1 is a semiconductor laser (LD), 2. 3.4 is a lens; 5 is a reflecting plate made of, for example, a metal evaporated mirror or a diffraction grating; 6 is a minute displacement element, such as PZT, for adjusting the position of the reflecting plate 5 in the optical axis direction; and 7 is an optical fiber. , the rear end face of the semiconductor laser 1, the lens 2, and the reflection plate 5 constitute an external resonator a.In Fig. 2, the light emitted from the rear end face of the semiconductor laser 1 becomes a parallel light beam at the lens 2, The parallel light beam is reflected by the reflecting plate 5, returns along the same optical path as the parallel light beam from the lens 2, and is coupled to the semiconductor laser 1 via the lens 2.

Such optical feedback phenomenon results in the formation of an external resonator a having a resonator length longer than that of the semiconductor laser 1 itself, and the external resonator a has an optical property of the emitted light of the semiconductor laser 1. Since it is a major factor in determining However, in order to obtain optically stable output light, the optical phase of the external resonator a must match the optical phase of the resonator inside the semiconductor laser 1, and in order to make these optical phases match, In addition, by slightly displacing the position of the reflection plate 5 in the optical axis direction using a minute displacement element 6 attached to the reflection plate 5, the length of the external resonator a was changed to adjust the optical phase.

(Problem to be Solved by the Invention) However, according to the above configuration, when the minute displacement element 6 is operated, the feedback light beam will cause an angular shift when the angular displacement δ shown in FIG. 3 occurs. Become. Therefore, the optical path of the light beam, which is not easily affected by axis misalignment but extremely susceptible to angular misalignment, is significantly shifted, and the amount of light returned to the semiconductor laser 1 is reduced, causing the laser beam to There were problems such as the line width of the emitted light becoming wider and so-called mode hopping occurring.

SUMMARY OF THE INVENTION In view of the above-mentioned problems, an object of the present invention is to prevent the angular shift of the returned light beam from occurring even if an angular displacement occurs.
Therefore, it is an object of the present invention to provide a semiconductor laser module with an external cavity in which the amount of light returned to the semiconductor laser does not decrease and the optical characteristics of the laser emitted light are stable.

(Means for Solving the Problems) In order to achieve the above object, the present invention provides a lens that converts light emitted from one end surface of a semiconductor laser into a parallel light beam, and a lens that reflects the parallel light beam and returns it to the lens. In the semiconductor laser module with an external cavity, the prism is disposed in the optical path of the parallel light beam so that its light transmitting surface faces the lens and the reflector.

(Function) According to the present invention, the light emitted from one end surface of the semiconductor laser is converted into a parallel light beam by the lens, enters the prism, is reflected by the reflective surface of the prism, and is emitted from the prism to become a parallel light beam from the lens. It propagates in the opposite direction and reaches the reflector. The light beam reaching the reflector is reflected and propagates through the lens and prism on the same optical path that reached the reflector, ie, is recombined to the semiconductor laser via the prism and lens.

(Embodiment) FIG. 1 is a configuration diagram showing an embodiment of a semiconductor laser module with an external cavity according to the present invention. Components having the same configuration as the above-mentioned conventional example shown in FIG. 2 are designated by the same reference numerals. represent. That is, 1 is a semiconductor laser (LD), 2 is a lens,
5 is a reflecting plate, for example a metal vapor deposited mirror, and 6 is a minute displacement element, for example PZT.

Reference numeral 10 denotes a prism, which is disposed such that its light transmitting surface 10a faces the lens 2 and the reflecting surface 5a of the reflecting plate 5. A is configured. Further, a minute displacement element 6 for displacing the prism 10 in the optical axis direction is attached to the outside of the intersection of the reflective surfaces of the prism 10, so that the position of the prism 10 in the optical axis direction can be finely adjusted. There is.

In the semiconductor laser module having such a configuration, the light emitted from the rear end face of the semiconductor laser 1 is converted into a parallel light beam by the lens 2, and this parallel light beam is passed through the prism 1.
0, is reflected by the reflective surface 10/b of the prism 10, is further reflected by the reflective surface 10c, and is emitted as a parallel light beam from the transmitting surface 10g in the opposite direction to the parallel light beam and is reflected. Reach board 5. Reflector plate 5
The parallel light beam that has reached is reflected by the reflecting surface 5a and is coupled to the rear end facet of the semiconductor laser 1 again through the same optical path as a return light beam. In this way, from the rear end face of the semiconductor laser 1, the reflection plate 5 is
The external resonator A is functioning with the distance up to the resonator length as the resonator length. In addition, a minute displacement element 6 attached to the prism 10
For example, when the prism 10 is displaced in the optical axis direction by a distance indicated by d in FIG. 1, the resonator length of the external resonator A is displaced by a distance of 2d. Therefore, if the possible displacement length of the micro-displacement element 6 is d', this external resonator A is capable of adjusting the optical phase of the external resonator A and the semiconductor laser 1 within a range of 2d-, which is twice the possible displacement length. It is possible to adjust the optical phase of the internal resonator.

Next, the optical path of the parallel light beam inside the external resonator A when the angular displacement δ occurs in the prism 10 will be explained with reference to FIG. First, when there is no angular displacement as shown by the solid line in FIG. It is reflected and returns to the same optical path, i.e. the optical path■
, are returned to the optical path (2) via the prism 10. here,
As shown by the two-dot chain line in FIG. 4, when an angular displacement δ occurs in the prism 10, the light beam propagating along the optical path ■ propagates through the prism 10 and deviates from the optical path ■.
reaches the reflecting plate 5, and is reflected by the reflecting plate 5. However, the light beams that have passed through the prism 10 are parallel even though their optical paths are different, so the light beam reflected by the reflecting plate 5 is The same optical path as , that is, the optical path ■, and the optical path ■ by transmitting the prism 10
will be returned to. Therefore, even if an angular displacement δ occurs, the transmission surface 10 of the prism 10 is
The optical path up to a coincides with both the outgoing path and the incoming path.

According to this embodiment, the lens 2 of the external resonator A and the reflector 5
By arranging the prism 10 to which the minute displacement element 6 is attached in the optical path, even if an angular displacement occurs in the prism 10 when the minute displacement element 6 is operated, the return light beam reflected by the reflection plate 5 will be prevented. Since there is no angular shift and therefore there is no risk of reducing the amount of light returned to the semiconductor laser 1, it is possible to realize a semiconductor laser device with stable optical characteristics. Further, since the possible displacement length of the external resonator A is twice that of the minute displacement element, a low-cost minute displacement element can be used, and the cost of the device itself can be reduced.

By using a tetrahedral prism with three reflecting surfaces, that is, a corner cube prism, as the prism 10, even if an angular displacement occurs in a direction perpendicular to the angular displacement direction explained in FIG. A similar effect can be obtained, and it is also possible to deal with three-dimensional angular displacement.

In addition, although a metal-deposited mirror is used as an example of a reflecting plate, it is not limited to this. For example, if an interference film mirror is used instead of a metal-deposited mirror, the reflectance of the light beam can be improved, and the diffraction The use of gratings allows wavelength selection of the light beam.

(Effects of the Invention) As explained above, according to the present invention, there is provided a lens that converts light emitted from one end surface of a semiconductor laser into a parallel light beam, and a reflection plate for reflecting the parallel light beam and returning it to the lens. In the semiconductor laser module with an external cavity, a prism is disposed in the optical path of the parallel light beam so that its light transmitting surface faces the lens and the reflecting plate, so that an angular shift may not occur in the returned light beam. There is no. Therefore, since there is no risk of reducing the amount of light returned to the semiconductor laser, it is possible to realize a semiconductor laser device with stable optical characteristics without increasing the spectral line width of the emitted light or causing mode hopping, etc. This has the advantage of greatly improving the reliability of optical communication systems.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of a semiconductor laser module with an external cavity according to the present invention, FIG. 2 is a block diagram of a conventional semiconductor laser device with an external cavity, and FIG. 3 shows the angular displacement of the conventional device. FIG. 4 is a diagram for explaining the optical path of a light beam when angular displacement occurs in the present invention. In the figure, 1... Semiconductor laser (LD), 2... Lens, 5... Reflector, 6... Minute displacement element, 10...
・Prism, A...External resonator. Patent Applicant: Oki Electric Industry Co., Ltd. Agent Patent Attorney: Yoshi 1) Takashi Sei

Claims (1)

[Scope of Claims] A semiconductor laser with an external cavity, comprising a lens that converts light emitted from one end surface of the semiconductor laser into a parallel light beam, and a reflector for reflecting the parallel light beam and returning it to the lens. 1. A semiconductor laser module with an external cavity, characterized in that a prism is disposed in the optical path of the parallel light beam so that a light transmitting surface faces the lens and the reflecting plate.