Sum and difference frequency generation as diagnostics for leaky eigenmodes in two-dimensional photonic crystal waveguides

Abstract

We experimentally demonstrate how sum frequency generation (SFG) and difference frequency generation (DFG) of 150fs pulses can be enhanced and serve as diagnostics for leaky eigenmodes in a two-dimensional GaAs photonic crystal waveguide. SFG at 795nm is obtained in reflection from s-polarized 1900nm and p-polarized 1360nm pulses, with both input beams coupled to leaky eigenmodes; the SFG is enhanced by >350× compared to that from an untextured GaAs surface. We are able to detect Drude induced subnanometer blueshifts of the SFG, corresponding to refractive index changes of ⩽10−3. DFG of 1360nm light obtained in reflection from s-polarized 1900nm and p-polarized 793nm pulses displays an enhancement of >500× via three different leaky eigenmodes. As the 793nm beam polarization is varied from p polarized to right and left circularly polarized, the DFG remains essentially linearly polarized but with a reduced, albeit different, intensity for right and left circularly polarized 795nm pulses. Futhermore, the plane of polarization also rotates by different amounts for the left and right circularly polarized light, demonstrating interference of the components generated by s- and p-polarized 793nm pulses. Overall, our results demonstrate how enhanced DFG and SFG from leaky eigenmodes can be used to characterize their properties more precisely than linear optical techniques.