TAPERED OPTICAL FIBER GRATING DEVICE INCLUDING VARIABLE REFRACTIVE INDEX COATING FOR CORRECTING WAVEGUIDE CHARACTERISTIC OF BASIC MODE

摘要

PROBLEM TO BE SOLVED: To permit regulation or turning in order to supply different spectrum molding characteristics by enclosing the tapered region of a fiber with a coating in order to change the spectral molding characteristics of gratings, thereby correcting the effective waveguide refractive index of the basic mode of the fiber. SOLUTION: The fiber 12 includes the tapered region 18 including a portion 20 of the smallest outside diameter and two tapered thermal insulating portions 22. The tapered region 18 within the region of the gratings is covered by the coating 26 of a variable refractive index material. The tapered region 18 executes operation free from loss to introduce the portion where the basic mode cannot be disregarded to the coating 26 enclosing cladding 16 when light passes the tapered region 18. The coating 26 may be used to selectively correct the effective waveguide refractive index of the basic mode when the basic mode expands to the outside of the cladding 16. As a result, the turning or regulation of the optical spectrum molding characteristics of the grating is made possible.