Birefringence relaxation in photosensitive polymer optical fiber preform

The birefringence relaxation of photosensitive polymer optical fiber preform with low azo concentration is analyzed. Instead of bi-exponential function, tri-exponential one is introduced to describe the relaxation process. Three types of relaxation are given considering the movements of chromophores, side chains, and main chains. The conserved birefringence, which depends on the orientation of main chains, is also studied through comparison of three kinds of materials with different interaction between side chain and main chain.