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

We propose a fiber-pigtailed strained silicon platform for tunable difference frequency generation (DFG) in mid-infrared (MIR) with tunable continuous wave near-infrared (NIR) sources. Stress exerted by silicon nitride induces second-order nonlinear susceptibility c(2) on underlying centro-symmetric silicon. NIR light is coupled into silicon and MIR light is coupled out of silicon using sub-wavelength grating couplers respectively. Phase 1 research showed feasibility of low fiber insertion loss and low propagation loss silicon waveguides on the silicon-on-insulator platform at NIR pump and signal and MIR idler wavelengths. Quasi phase matching (QPM) will be employed with periodically patterned strained silicon nitride induced c(2) to generate efficient DFG. Preliminary QPM designs indicates potential to achieve conversion efficiency 11.67%W-1 in periodic tensile strained and 47.15%W-1 in periodic tensile and compressive strained silicon nitride with c(2) ~ 40pm/V in a silicon waveguide of effective length 1.3cm. Periodic DC electric field induced c(2) effects will also be studied. Two-photon absorption (TPA) and particularly TPA induced MIR free carrier absorption will be controlled by experimentally demonstrated p-i-n geometries that reduce silicon free carrier lifetime from nano-seconds to picoseconds. The DFG source will be integrated with previously demonstrated silicon based slotted slow light absorbance sensor for commercialization success.