We have demonstrated, for the first time, the suppression of cladding mode coupling loss to 0.1 dB in 30-dB fiber Bragg gratings for both nonhydrogenated and hydrogenated fibers. These fibers have also been optimized to give 0.04-dB average splice loss to SMF-28 fiber. The suppression of cladding mode coupling is achieved by accurately characterizing and controlling the photosensitive profile. This low level of cladding mode coupling loss has opened up a new range of broadband applications, previously restricted by the limited free spectral range of fiber Bragg gratings.
Liang Dong, Gang Qi, Marlene Marro, Vikram Bhatia, Lisa L. Hepburn, Martin Swan, Adam Collier, and David L. Weidman, "Suppression of Cladding Mode Coupling Loss in Fiber Bragg Gratings," J. Lightwave Technol. 18, 1583- (2000)