JPS6461711A - Optical fiber coupler - Google Patents

Abstract

PURPOSE:To decrease an excessive loss to <=1dB by producing a low-loss polarization maintaining optical fiber coupler by using double-refractive optical fibers which are ordinarily produced and are lower in the refractive index of the stress imparting part than the refractive index of a clad. CONSTITUTION:Two pieces of the double-refractive optical fibers 31, 32 consisting of the core 35, the clad 36 which encloses the core 35 and is lower in the refractive index than the core and the stress imparting parts 37, 38 which are disposed on both opposed sides of the core 35 and have the refractive index lower than the refractive index of the clad 36 and the coefft. of thermal expansion different from the coefft. of thermal expansion of the clad 36 are used. Two pieces of these double-refractive optical fibers 31, 32 are partly longitudinally fusion spliced and stretched to each other by unifying the main axes of polarization of the double-refractive optical fibers, by which the optical fiber coupler is produced. The coupler obtd. in such a manner satisfies the conditions expressed by formula I, where the wavelength of the light to be used is designated as lambda, the refractive index of the clad 36 of the double- refractive optical fibers 31, 32 as (n), the diameter in the major axis direction of the section in the finest part of the fusion spliced and stretched part as (b) and the number pi as pi6.