Complex rhombus lattice photonic crystals for broadband all-angle self-collimation

Abstract

In this paper, we discuss two-dimensional photonic crystals of complexrhombus lattice structures to enable broadband, ‘all-angle’ light collimation.The proposed structures are made of complex elliptical dielectric rods (ε = 12) embedded in an air background. Based on the equi-frequency contours (EFCs) calculated bythe plane wave expansion method (PWEM), these structures show a wide range of open, nearlyflat EFCs, with the maximum angular deviation from the primary collimating direction less than2°. The broadest relative range of these open, nearly flat EFCs found is 17% of a chosencentral wavelength. For a sample element centered at 1550 nm, this range coverswavelengths from 1429 to 1695 nm; the devices can be scaled to cover alternativewavelength ranges. These structures could benefit applications that require a broadoperating wavelength range. Potential applications include collimating beam combiners,multiplexers and solar light collectors.