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.
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