Photorefractive polarization couplers in elliptical core fibres

Photorefractive polarization couplers written internally in germanium-doped elliptical core fibers at 488, 514, and 532 nm are reported. Complete power transfer between the orthogonal polarization modes of the fiber was achieved for couplers written at 514 and 488 nm, respectively. It is shown that the couplers are nonuniform in length because of the high photoinduced attenuation and also due to two-photon absorption. Polarization coupling of higher order modes is also demonstrated at shorter wavelengths where their polarization beat lengths match the polarization beat length of the fundamental mode at which the coupler was written.<>