Broadband mid-infrared generation by difference-frequency generation in strongly dispersive Bragg reflection waveguides

Abstract

We present a novel scheme for generation of broadband mid-infrared (mid-IR) radiation using a quasiphase-matched difference-frequency-generation (DFG) process in a planar high index core symmetric Bragg reflection waveguide (BRW) geometry based on GaN/AlxGa1−xN system. By suitably tailoring the dispersion properties of the BRW so as to maintain the phase-matching condition over a broad range of pump wavelengths, we show that the pump acceptance bandwidth could be enhanced by nine to ten times for a DFG process. This manifests into a broadband mid-IR difference-frequency idler with greater than 280 nm bandwidth close to 4.35 μm wavelength. Since the design presented here exploits the dispersive features of the BRW; we can shift the broadband characteristics to any desired region of the mid-IR spectrum within the constraints imposed by transparency and nonlinearity of the constituent materials. The design also facilitates pumping by standard high-power solid-state laser sources.