Highly reflective polymer fiber Bragg grating and its growth dynamics

Summary form only given. A polymer fiber Bragg grating with reflectivity higher than 99.8% is fabricated by interferometric side exposure of the fiber core to a UV pulse at 325 nm. The linewidth is less than 0.5 nm. Experimental results also show that the behavior of polymer fiber Bragg grating growth versus UV pulse energy is similar to that of silica fiber Bragg gratings. There is also a threshold of pulse energy, above which the induced index modulation increases dramatically. Below the threshold point, the index modulation grows linearly. So for the region when /spl utri/n increases linearly, it is just comparable to type I gratings in silica fiber. When the POF Bragg grating is over-exposed, the transmission rejection level stays the same, while the loss to the lower wavelength increases and the linewidth becomes larger. This is just comparable to type II gratings of silica fiber. Another outstanding feature is that the Bragg wavelength shifts to the blue part of the spectrum in the course of the grating inscription, which indicates that the induced refractive index modulation by POF Bragg grating is negative.