LONG-CYCLE- FIBER GRATING DEVICE

摘要

PROBLEM TO BE SOLVED: To improve stability to a temperature change by specifying the effective refractive index of the clad layer of the core of an optical fiber and a speed change with respect to the temperature, thereby forming a long period grating formed with the core having the perturbations of the refractive index. SOLUTION: The core 11 of the optical fiber 10 has a plurality of perturbations 15 of the refractive index arranged at periodic intervals, by which the long period grating 14 of a central wavelength λp is formed. The clad layer 12 enclosing the core 11 has the effective refractive index smaller than the effective refractive index of a core waveguide mode and the average change rate with respect to the temp. has the value sufficiently approximate to the average change rate with respect to the temp. of the core 11. Further, the change rate with respect to the temp. of the central wavelength λp is specified to <=4nm/100 deg.C. The clad layer is preferably a composite clad layer consisting of a first part 12 adjacent to the core 11 and having the refractive index lower than the refractive index of the core 11 and the second part 13 adjacent to the first part 12 and having the refractive index higher than the refractive index of the first part 12.