Photoinduced polarisation couplers in elliptical core optical fibres written using 532 and 266 nm sources

The writing of photoinduced polarisation couplers in elliptically cored singlemode fibres by the internal method at 532 nm and by the external point-by-point method at 266 nm is reported, providing a direct comparison of the photoinduced birefringence at these wavelengths. The possibility of writing narrow linewidth couplers in short sections of elliptical-core fibres operating at low values of normalised frequency is also demonstrated.