Characterization of photoinduced birefringence change in optical fiber rocking filters

We investigate the effects of UV exposure on the growth of optical fiber rocking filters written in hydrogen-loaded germanosilicate elliptical core fibers. We find that with increasing exposure, the rocking angle (induced birefringence) increases rapidly then begins to decrease, eventually erasing completely. With further exposure, the rocking angle is seen to increase again, reaching values of 3.5 degrees. This corresponds to a photoinduced birefringence almost four times larger than previously recorded in optical fiber rocking filters. Furthermore, we show that at high UV fluences, the direction of rotation of the birefringent axes is opposite to that at low fluences. (C) 1996 American Institute of Physics.