Silicate photonic crystal fibers with rectangular lattice and elliptical holes

Abstract

ABSTRACT In this paper we report on progress in optimization of the ma terial and structure of photonic crystal fibers for use as an element of fiber sensor of strain and temperature. The fabricated photonic structures consist of elliptical-like holes ordered in rectangular lattice. The rectangular lattice is applied to obtain global asymmetry of photonic structure with two-fold geometry and to create birefringence of fiber. Elliptical air holes allows to increase birefringence in the structure up to the order of 10 –2 for wavelength of 1.55 P m, theoretically. Additionally, rectangular lattice gives a better control of elliptical air holes uniformity during fabricating process. For fabrication of the fibers we use NC21 boro-silicate glass. Use of high quality glass allows omitting problem s with very high attenuation of the previously fabricated highly birefringent photonic crystal fibers made of SK222 glass. With full vector plane-wave expansion method an influence of structure parameters such as ellipticity of air holes and aspect ratio of rectangular lattice on birefringence and modal properties of the fiber is studied. In this paper we present optimization of the fiber structure design, which takes into account technological limits of fabrication of elliptical holes in fibers. Theoretical birefringence is compared with experimental measurements. Experimental results already obtained allows to predict birefringence at the order of 10 –3 for wavelength of 1.55 P m for optimized photonic cladding of the fibers. Keywords: birefringence, photonic crystal fibers, microstructured fibers, polarimetric sensors