Fiber Pigtailed On-Chip Mid-infrared Difference Frequency Generation in Silicon

Omega Optics will develop a fiber-coupled platform in strained silicon-on-sapphire (SoS) for tunable difference frequency generation in midwave infrared (MIR) with tunable continuous wave sources in the near-infrared (NIR). Stress exerted by silicon nitride on underlying silicon induces second-order nonlinear susceptibility. NIR light is coupled into silicon and MWIR light is coupled out of silicon using extensively demonstrated sub-wavelength grating couplers in both NIR and MWIR. Preliminary modal phase matched designs between pump, signal and idler indicates the potential to achieve conversion efficiency greater than 0.1W-1 with second-order nonlinear susceptibility ~10pm/V in a 1cm long silicon waveguide on sapphire. Experimentally demonstrated sub-1dB/cm propagation loss at NIR pump and signal wavelengths, ~2dB/cm propagation losses in MWIR idler wavelengths in silicon waveguides, together with less than 2.5dB insertion loss in fiber-chip polarization selective grating coupling allow high efficiency power conversion. Two-photon absorption (TPA) and in particular, TPA induced free carrier absorption (FCA), significant at MWIR will be controlled by experimentally demonstrated p-i-n geometries that reduce the silicon free carrier lifetime from nano-seconds to pico-seconds. Fabrication induced effects on coherence and geometries to achieve quasi phase matching will also be investigated, relative merits and demerits compared for implementation in Phase II.