Fiber Bragg reflectors by single excimer pulse

In-fiber Bragg reflectors produced with coherent, transverse UV illumination promise to be versatile optical elements for spectral selection and distributed sensing. These fiber devices were generated by repetitive exposures to a moderate intensity, frequency-doubled dye laser under holographically stable conditions until sufficient periodic index modulation had accumulated to produce a strong reflection. Fluences in the range of 1000 J/sq cm were delivered over the course of many seconds to minutes to obtain an index modulation depth of about 1 x 10 exp -4. In an alternate approach, we used single about 1 J/sq cm pulses from a line-narrowed KrF excimer to produce gratings with a modulation depth of about 2 x 10 exp -5, and more recently have achieved values above 1 x 10 exp -4. An unanticipated benefit of the single-pulse preparation method appears to be the markedly enhanced thermal stability of the grating structure, as compared to that reported for gratings produced with multiple exposures.