Study on the photosensitivity of birefringent grating in copolymer optical fiber with high concentration

A novel copolymer optical fiber with high azobenzene concentration is reported (more than 3.2 mol %). The orientation process of the preform was fitted with corrected bi-exponential equation. Compared with the doped one, the photosensitivity of this kind of copolymer optical fiber preform is analyzed. The influence of azobenzene concentrations and write conditions on photosensitivity of copolymerized PMMA was analyzed. Then, long-period of 120um birefringent grating was fabricated in the single mode fiber with core refractive index of 1.485 (at wavelength of 1.5um), and relative index difference delta of 0.008. The duty cycle is 50%, and the refractive index change in the exposed area is about 4*10-4 for the ordinary or extraordinary ray.