Coupling structure between a semiconductor laser and an optical fiber and coupling method thereof

#The present invention relates to an optical coupling between a semiconductor laser and an optical fiber and, particularly, to a coupling structure for directly coupling a semiconductor laser and an optical fiber without using condenser means such as lens, etc., and a coupling method therefor.

#One of methods for optically coupling an output light of a semiconductor laser to an optical fiber is to use an optical condenser means such as lens, etc., for condensing an output light of the laser and coupling it to the optical fiber. The other method is to place an end face of an optical fiber in close proximity to an output end face of a semiconductor laser to couple an output light of the laser directly to the optical fiber.

#In either method, in order to reduce a coupling loss, the end face of the optical fiber is mirror-polished. This is because the coupling loss is considered as being increased by scattering if there is minute irregularity in the end face of the optical fiber (see, for example, Japanese Patent Application Laid-open No. S61-221705).

#The above mentioned and other objects, features and advantages of the present invention will becomes more apparent from the following detailed description when taken in conjunction with the accompanying drawings, wherein:

#FIG. 1 shows a coupling structure of a semiconductor laser and an optical fiber, according to the present invention;

#FIG. 2 shows a relation between surface roughness of an end face of an optical fiber and a return loss;

#The present invention will be described in detail with reference to the drawings.

#FIG. 1 is a longitudinal cross section of a coupling structure of a semiconductor laser and an optical fiber, according to the present invention. Similarly to the conventional coupling structure, an output light 2 of the semiconductor laser 1 is directly coupled to a core 5 of the optical fiber 4 by arranging an end face 6 of the optical fiber 4 in close proximity to an end face 3 of the semiconductor laser 1. In this embodiment, the semiconductor laser 1 emits light having wavelength of 1.3 .mu.m with emitting angle of 32 degree. Further, the optical fiber used is of a single mode quartz fiber having core diameter of 10 .mu.m.

#The end face 6 of the optical fiber 1 used in the present invention has an average surface roughness Rz in a range from 0.04 .mu.m to 0.06 .mu.m. Incidentally, surface roughness Rz of the conventional mirror-polished end face is in the order of 0.01 .mu.m. Therefore, the surface roughness of the end face in the present invention is larger than that of the mirror-finished end face. Further, the surface roughness of the end face of the present invention is smaller than the wavelength of 1.3 .mu.m of the laser light.