We have demonstrated fast formation [~1500 pulses at ~1 (J/cm2)/pulse] of fiber gratings with highly negative index modulations (~-3 × 10-4). We have found that the maximum negative index modulations that are achieved do not depend on the pulse intensities, although the inverse of the time taken to reach the negative index-modulation maximum varies linearly with the pulse intensities. This prompts us to use a three-energylevel system to model the photosensitivity in boron-doped germanosilicate fiber. All the necessary parameters of the model can be determined from a single growth measurement of the average index change, and the model’s prediction fits well the measured index-modulation growth.
© 1996 Optical Society of America
L. Dong, W. F. Liu, and L. Reekie, "Negative-index gratings formed by a 193-nm excimer laser," Opt. Lett. 21, 2032-2034 (1996)