Analysis of ultra refraction properties in strong index contrast slab photonic crystals

This paper deals with the theoretical analysis of ultra refraction properties of slab photonic crystals. Strong angular dispersions induced by wavelength variations have been experimentally observed near the Γ-M and Γ-K directions around λ = 1320 nm with negative and positive signs, respectively. An interpretation of these phenomena using three-dimensional plane wave method (3D-PWM) and finite-difference time-domain (3D-FDTD) calculations is presented. Equifrequency surfaces are obtained from PWM calculations and group velocities of Bloch waves excited in the patterned medium are predicted as a function of the incident wave wavelength and wavevector orientation. FDTD calculations have been performed to evaluate the influence of the finite size of the structure and to estimate the photonic crystal coupling losses for various configurations. This theoretical approach allows identifying Bloch waves responsible for the observed properties.