Widely Tunable Optical Parametric Oscillation and Visible Light Generation in 4H‐SiC Microresonators

Widely separated optical parametric oscillation (OPO) represents a powerful method for coherent wavelength conversion across infrared and visible spectra. While such generation has been demonstrated in material platforms such as silicon nitride and lithium niobate, 4H‐SiC remains unexplored despite offering combined strong second‐order and third‐order nonlinearities with ultralow material loss. Here we demonstrate tunable, widely separated OPO generation in 4H‐SiC microresonators through dispersion engineering. By optimizing the resonator geometry to achieve normal dispersion at telecommunication wavelengths and pumping at around 1550 nm, a pair of signal and idler spanning nearly an octave is generated, which represents the first demonstration of widely separated OPO in 4H‐SiC. The frequency separation is tuned by varying the pump wavelength, with measured signal and idler wavelengths aligning well with phase‐matching predictions. Leveraging the non‐centrosymmetric crystal structure of 4H‐SiC, the generated OPO signal undergoes cascaded second‐harmonic generation (SHG) and sum‐frequency generation (SFG) with the pump, yielding coherent visible light at wavelengths below 700 nm. This cascaded upconversion of widely separated OPO signals represents a novel pathway for visible light generation. These results establish 4H‐SiC as a promising platform for nonlinear wavelength conversion spanning from visible to 2 µm region.