BIREFRINGENCE GRATING WITHIN A SINGLE MODE POLYMER OPTICAL FIBRE WITH PHOTOSENSITIVE CORE OF AZOBENZENE COPOLYMER

A single mode optical fibre with a core of azobenzene-containing copolymer instead of doped polymer was fabricated. A 120 m long-period birefringence grating with a 50 % duty cycle has been successfully written within the core of the fibre with 532 nm laser by a mask method. Under polarized microphotography, the grating was observed when the optical axis was set at 45 ° with the direction of the first polarizing lens of the polarization microscope. Although birefringence decayed gradually when writing laser was turned off, a permanent change of refractive index as much as 7.0 10-4 still has been observed in the material, which ensures the stability of written birefringence grating