Highly-birefringent elliptical structures

An analysis of isotropic multi-step fiber structures with elliptical geomet ry, in particular, the fiber structures which provide the large value of th e birefringence, is presented. The multi-layer confocal-elliptical fibers c an be analyzed by the exact analytical method with Mathieu function expansi ons. In that group of fibers, the W-profile elliptical fiber provides the l argest value of the birefringence. In order to investigate the three-layer elliptical fibers with layers of any ellipticity we apply the improved poin t-matching method with Mathieu function expansions. It was found that the h ighly-birefringent fibers with hollow layers outside an elliptical core can be suitable for the single-mode single-polarization transmission. Numerica l results are presented for the silica fibers doped GeO2 and F, respectivel y. The results obtained are of the practical value and can be used directly in designing the elliptical fibers with large value of the birefringence.