Properties of polarized laser-induced birefringent gratings in azobenzene-doped poly(methyl methecrylate) optical fibers

Birefringent gratings induced by 532 rim polarized laser in an azobenzene-doped polymethyl methacrylate (PMMA) fibers and blocks were investigated. Significant photo-induced birefringence with about 3.0 x 10(-5) has been observed from the fiber. It was found that there is an intensity threshold, which is 0.29 mW/cm(2) at 532 nm. The birefringence decayed gradually when the writing laser turned off. So the dynamic process of the birefringence was studied. Both the rise and the decay processes of the birefringence include an initial "fast" response mode and a subsequent "slow" response mode. Both the fast response and the slow response become faster with increasing irradiating laser intensity. The birefringence was induced by the combination of the nonlinear absorption, linear absorption and thermal effect. (C) 2002 Elsevier Science B.V. All rights reserved.