Second-Harmonic and Sum-Frequency Generation in Hybrid GaSe–SiN Waveguide

Silicon nitride (SiN) photonic platform offers ultralow linear and nonlinear propagation losses, wide optical transmission window, and CMOS-compatible fabrication processes, making it ideal for photonic integrated circuits with linear and nonlinear functions. However, SiN inherently lacks second-order nonlinear optical response (χ⁽²⁾) due to the centrosymmetry, which precludes χ⁽²⁾ processes such as second-harmonic generation (SHG) and sum-frequency generation (SFG). Here, we demonstrate a hybrid GaSe–SiN photonic platform that overcomes this intrinsic limitation and enables efficient second-order nonlinearities. By employing mode phase-matching and GaSe’s strong χ⁽²⁾, we achieve an SHG efficiency of 0.06%/W in straight GaSe–SiN waveguides with the pump of a continuous-wave laser. To further showcase the platform’s capability, an on-chip single-shot autocorrelator is realized based on SHG traces from the hybrid GaSe–SiN waveguide, enabling precise measurement of ultrashort pulse widths and the group refractive index of the waveguide mode. A hybrid GaSe–SiN microring resonator (MRR) is further fabricated, which presents resonance modes with quality factor of 3.6 × 10³. The resonance enhancement of the MRR promises efficient SHG and SFG with efficiency of 5300%/W and 2580%/W, respectively, corresponding to an effective χ⁽²⁾ around 5.7 pm/V. With fast development of wafer-scale growth and integration of two-dimensional materials, including χ⁽²⁾-enabled GaSe and InSe, the demonstrated platform promises high-efficiency χ⁽²⁾-processes in CMOS-compatible SiN photonics for nonlinear optical signal processing and characterizations.