High-Efficiency Second-Harmonic and Sum-Frequency Generation ina Silicon Nitride Microring Integrated with Few-Layer GaSe

A silicon nitride (SiN) photonics platform hasattributes of ultra-low linear and nonlinear propagation losses andCMOS-compatible fabrication processes, promising large-scalemultifunctional photonic circuits. However, the centrosymmetricnature of SiN inhibits second-order nonlinear optical responses inits photonics platform, which is desirable for developing efficientnonlinear active devices. Here, we demonstrate high-efficiencysecond-order nonlinear processes in the SiN photonics platform byintegrating a few-layer GaSeflake on a SiN microring resonator.With the pump of microwatt continuous-wave lasers, second-harmonic generation and sum-frequency generation with theconversion efficiencies of 849%/W and 123%/W, respectively, areachieved, which benefitfromGaSe's ultrahigh second-ordernonlinear susceptibility, resonance-enhanced GaSe-light interaction, and phase-matching condition satisfied by the modeengineering. Combining with the easy integration, the GaSe-assisted high-efficiency second-order nonlinear processes offer a newroute to enriching the already strong functionality of the SiN photonics platform in nonlinear optics.