OPTICAL FIBER COUPLER AND OPTICAL FIBER FOR OPTICAL FIBER COUPLER

摘要

PROBLEM TO BE SOLVED: To provide an optical fiber coupler whose excessive loss is sufficiently reduced. SOLUTION: Optical fibers 10 and 20 used for the optical fiber coupler 1 have a specific refractive index differenceΔn(r)<=Δnpeak [1-(r/a)3], where (r) is a radial distance from the center of the optical axis, An(r) is the specific refractive index difference at positions (r) in core parts 10a and 20a based upon the refractive indexes of clad parts 10a and 20b provided around the core parts 10a and 20a, and (a) is a core radius, providing that the specific refractive indexΔn(r) has a peak valueΔnpeak at a position rpeak . Further, the refractive indexes of the clad parts 10b and 20b gradually decrease radially outwards.