On-Chip Fabry–Perot Bragg Grating Cavity Enhanced Four-Wave Mixing

Optical microcavity based four-wave mixing (FWM) and its various applications, such as entangled photon pair generation, have been intensively studied in the past few years. Compared to the microring cavities that most researchers have been focusing on, here, we report the generation of FWM photons with Fabry–Perot Bragg grating cavities (FPBG) using the Si₃N₄/SiO₂ platform. By leveraging the large, nonuniform and symmetrical dispersion and tunability of our grating cavity, a unique strategy is established to compensate the strong normal dispersion of the waveguide and phase matching condition is achieved on a thin Si₃N₄ film, which is critical for efficient wavelength conversion. We develop an analytical model to optimize the nonlinear conversion efficiency of FWM, and we also introduce tapered grating in the FPBG to reduce the grating loss from 3.5 dB/cm to 0.36 dB/cm. With a 5.3 dBm pump power, the nonlinear conversion efficiency is characterized to be −37.7 dB. Our work demonstrates that FPBG is a promising on-chip platform for entangled photon pair generation and quantum communication applications.