Refractive-index changes of standard telecommunication fiber through exposure to femtosecond laser pulses at 810 cm

We report on permanent refractive-index changes as great as 6 X 10(-3) in standard fibers on irradiation with tightly focused femtosecond (120-fs) near-IR (lambda = 800-nm) pulses. The refractive-index increase was measured through changes in the transmission spectrum of an UV photowritten Bragg-grating-based Fabry-Perot interferometer. We depict the dependence of the index variation on exposure time. The changes in refractive index can be optimized after a few seconds of irradiation. The measured induced excess loss increases during near-IR exposure. (C) 2001 Optical Society of America.