Investigation on the confinement loss of index-guided photonic crystal fibers in the visible spectrum

This paper presents a comparative study of confinement ability of two 4-ring hexagonal lattice index-guided PCFs with different air-hole spacing (pitch) in the visible spectrum. The structure of PCF is designed and analyzed by using the Finite Element Method (FEM) with anisotropic perfectly matched layers. From analysis and comparison of the two optimized PCF structures, it can be investigated that the confinement loss is very low in the structure designed with d/Λ=0.5 and Λ=1.4 μm, where the light is single mode and confined in the core for the visible region (400-700) nm. A low confinement loss and low birefringence of the order of 10^-3 and 10^-4 respectively are obtained for this PCF. Also the effective area is found to be nearly 2-3 μm² and non-linearity co-efficient as 198-82 km^-1w^-1 respectively in the desired spectrum. This extremely high confinement ability in the visible range and non-linearity makes it promising for non-linear and sensing applications.