In this paper, the difference of core-mode effective refractive indices (RIs) and the long-period fiber grating (LPFG) resonant wavelength in an uniaxial-crystal fiber resulted from two fiber analysis models were demonstrated and analyzed. The two models are two-layered medium model which is normally used for conventional single-mode optical communications fiber and three-layered medium model. Using Transfer Matrix Method (TMM) based on Coupled-Mode Theory (CMT), the different dispersion properties of chirped long-period fiber gratings (CLPFG) calculated by both models were compared. The result shows that the difference of the core-mode effective RIs is significant especially when the cladding radius and cladding mode order are small, which indicates the limitation of the two-layer model, and that reducing the cladding radius and increasing the cladding mode order can improve the CLPFG dispersion compensation capability effectively. This paper provides guidance to the design and accurate analysis of CLPFG based dispersion compensator (DC).

A dual-core photonic crystal fiber (PCF) with high birefringence, short coupling length and broadband flat dispersion is proposed in the paper. The symmetry of the original symmetric structure composed of hexagonally distributed air holes is distorted by replacing the innermost 12 air holes with 6 elliptical air holes. The characteristics of the dual-core PCF such as birefringence, coupling length and chromatic dispersion are analyzed by tuning its structural parameters. The results demonstrated that the dual-core PCF exhibits simultaneously a birefringence of up to 10-2, a coupling length of 68.178 for the x-polarization and 74.825 for the y-polarization, and a broadband flat dispersion ranging from 1.1 to 1.6. The novel dual-core PCF may find applications in polarization-maintaining fibers and fiber-based polarization beam splitters/couplers with broadband flat dispersion.