JPS6315564B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a coupler that efficiently injects light from a semiconductor laser into an optical fiber.

Conventionally, various couplers have been proposed in order to effectively inject light from a semiconductor laser into a fiber. If the total amount of light emitted from the semiconductor laser is P _T and the amount of light injected into the fiber therein is P _F , then the closer the coupling efficiency K expressed by P _F /P _T is to 1, the better the coupler will be. However, in conventional couplers, as K approaches 1, the fiber injection surface into which light is injected and the amount of light reflected back through the fiber from the outside also increase proportionately. For this reason,
This reflected light makes the oscillation of the semiconductor laser, which is the light source, extremely unstable, and in some cases, oscillation becomes impossible.

The object of the invention is to provide a semiconductor laser coupler which eliminates the above-mentioned drawbacks. That is,
SUMMARY OF THE INVENTION It is an object of the present invention to provide a semiconductor laser coupler that prevents not only return light reflected at the end face of an optical fiber, but also light reflected at the proximal end of the optical fiber and returned through the cladding of the optical fiber. According to the present invention, it is possible to obtain a semiconductor laser coupler that eliminates the influence of reflection by using two types of anti-reflection pieces and a single mode fiber.

Next, the present invention will be explained in detail using the figures.

FIG. 1 is a diagram showing the configuration of a conventional coupler. A coupler 10 includes a semiconductor laser diode 11 having electrodes 12 and 13, and a rod lens 1 for condensing the emitted beam from the diode 11 to one point.
4 and an optical fiber 15 into which light from the lens 14 is injected. As shown in the figure, the light emitted from the semiconductor laser diode 11 is
The light is focused on one point by the rod lens 14. By fixing the end face of the optical fiber 15 at the focal point, most of the light from the diode 11 is injected into the optical fiber 15, resulting in an effective amount of light propagating within the optical fiber. The optical fiber 15 is assumed to be a multimode fiber, and the diameter of the effective area indicated by diagonal lines in FIG. 1 is usually 50 μ to 100 μ. An optical connector is attached to the other end of the fiber 15 for connection to external fibers or other components and devices. However, a coupler having such a configuration has a drawback that the reflected light generated at the injection surface of the optical fiber 15 on the semiconductor laser diode 11 side returns to the semiconductor laser diode 11, making the diode unusable. To avoid this, optical fiber 15
Although it is conceivable to form an anti-reflection film on the injection surface of the fiber 15, since the outer diameter of the fiber 15 is generally 1 mm or less, formation of such a film is impossible in terms of manufacturing. On the other hand, as a structure for preventing the above-mentioned reflection, there is a structure in which the position of the fiber injection surface is shifted back and forth with respect to the lens 14, as shown in FIG.
Although this configuration can reduce the effect of reflection on the fiber injection surface, it is possible to reduce the position of the fiber injection surface by
As shown in the figure, since the position is shifted by l1 or l2 from the optimum position, the coupling efficiency K deteriorates. Furthermore, the influence of the reflected light returning from the other end of the optical fiber 15 is not reduced at all. Furthermore, in FIG. 2, if a single mode fiber is used instead of the optical fiber 15, the coupling efficiency will be less than 0.05, which is completely impractical.

FIG. 3 is a diagram showing an embodiment of the present invention.
This embodiment is characterized by using a light shielding plate 31 made of a non-reflective material having light passage holes, an anti-reflection glass plate 32 and a single mode optical fiber 34 instead of the conventional multi-mode optical fiber 15. It is said that First, a non-reflective film is formed on both ends of the rotary lens 14. Further, an anti-reflection film for preventing reflection of light from the lens 14 is formed on the lens-side surface of the anti-reflection glass plate 32. The single mode fiber 34 and the antireflection glass plate 32 having the same refractive index as the fiber 34 are the fiber 34.
Since it is adhesively fixed by an optical matching material having the same refractive index as that of , no reflection occurs. Also, the reflection caused by the connection (optical connector or fixed connection) at the other end of the single mode fiber 34 is
Since the effective diameter of the single mode fiber 34 is extremely small, 5μ to 10μ, the amount of light that reaches the light emitting surface of the semiconductor laser diode 11 through the effective optical path of the fiber 34 is minute, so it has no effect on the diode 11. I won't give it. However, the amount that reaches the light emitting surface of the semiconductor laser diode 11 through the ineffective portion (cladding), which is a high-loss portion of the fiber 34, is ignored if the length to the connection point at the other end of the optical fiber 34 is short. Can not. The light shielding plate 31 is provided for this purpose, and prevents externally reflected light that has passed through the inactive portion of the optical fiber 34 from reaching the light emitting surface of the semiconductor laser diode 11.

Incidentally, a non-reflective film is formed on the surface 31a of the reflected light blocking plate 31 corresponding to the lens 14, or the material of the light blocking plate 31 itself is made of a non-reflective material.
Reflection of light from the lens 14 is prevented.

As described above, since the semiconductor laser coupler according to the present invention does not include a reflection generation element, stable oscillation of the laser diode can be connected. The coupling efficiency of the coupler according to the present invention can be expected to be about 0.2. Furthermore, even if a multimode fiber with an effective diameter of 50μ to 100μ is connected to the other end of the optical fiber 34 fixed to the coupler, the effective diameter is sufficiently larger than the effective diameter of the single mode optical fiber 34. The loss is minimal. Therefore, the semiconductor laser coupler according to the present invention has not much difference in coupling efficiency from the conventional one, has complete anti-reflection measures, and can connect both multimode fiber and single mode fiber with almost the same loss. It has great advantages such as versatility.

[Brief explanation of the drawing]

1 and 2 are diagrams showing a conventional coupler,
FIG. 3 is a diagram showing an embodiment of the present invention. In FIG. 3, 31... light shielding plate, 32... antireflection glass plate, 34... single mode optical fiber, 3
3...An optical alignment material for adhesively fixing the antireflection glass plate 32 and the single mode fiber 34.

Claims (1)

[Claims] 1 A semiconductor laser, a lens that focuses light from this laser, a single mode optical fiber through which light from this lens is incident on the core, and a single mode optical fiber that is attached to the light input end face of this fiber and that is attached to the light input end face to prevent reflection at the light input end face. and a light-shielding plate disposed on an end surface of the glass plate on the lens side and having a hole through which light emitted from the lens passes and blocks light other than the emitted light. combiner.