Polarization independent focusing of light by gradually modulated annular photonic structure

In this manuscript, we propose the design of an inhomogeneous artificially modeled graded photonic crystal (PC) medium to control and enrich the polarization insensitive focusing ability of light by using annular type all-dielectric materials. To obtain the graded annular PC structure, the lattice spacing along the transverse direction is modulated according to a parabolic function. The inner and outer radii of the annular PCs are optimized to attain frequency response of the graded structure. Even though the frequency responses of the transmission spectrum for different radial parameters exhibit different oscillation patterns for both TE and TM polarizations, optimum radii are determined where overlapping high transmission region is observed. Light focusing characteristics at those overlapping frequency regions are systematically and quantitatively investigated. Polarization insensitive focusing is achieved for bandwidth corresponding to ~6%. The designed structure can be used in integrated nanophotonics as a compact optical element with flat surfaces operating at both polarizations with high power transmission efficiency.