Quasi-Phase-Matched Four-Wave Mixing Enabled by Grating-Assisted Coupling in a Hybrid Silicon Waveguide

Phase matching must be performed to realize four-wave mixing (FWM) in a silicon waveguide, which is challenging when a signal wavelength is highly deviated from an idler wavelength. To solve this problem, quasi-phase-matching (QPM) based on grating-assisted directional coupling (GADC) in a hybrid structure is theoretically investigated. The proposed system consists of a silicon strip with periodic width modulation as the grating and a silicon nitride strip that is vertically aligned to the silicon strip. GADC occurs between the TES mode (mainly confined in the silicon strip) and TEN mode (mainly confined in the silicon nitride strip) at an idler wavelength. This phenomenon compensates for the phase mismatch occurring in FWM among the TES modes at the pump, signal, and idler wavelengths. Results of analysis of the hybrid structure show that the TES and TEN modes at an idler wavelength of 2.1177 mu m are efficiently generated with the TES modes at a pump wavelength of 1.58 mu m and signal wavelength of 1.2601 mu m. Moreover, the signal TES mode can be efficiently implemented with the pump TES mode and idler TEN mode. Owing to the GADC characteristics, the conversion bandwidth of the signal is 0.8 nm; however, the signal wavelength can be thermally tuned, with a temperature change of 50 degrees C corresponding to a signal wavelength change of 3.6 nm. The hybrid structure with the GADC-based QPM can be used to generate and detect mid-infrared light with well-developed O-band and L-band devices.