All-van der Waals microcavities for low-loss nonlinear photonics.

Van der Waals (vdW) materials have emerged as a promising platform for next-generation nanophotonics and optoelectronics. However, employing vdW materials as a core photonic integration platform, rather than as passive or active overlays on conventional silicon-based platforms, remains challenging, leaving their full potential untapped. Here we develop a nanofabrication strategy that enables high-resolution patterning across a broad range of vdW materials, including insulators, semiconductors, ferroelectrics and their heterostructures, and we show that they can be used as the intrinsic platform for low-loss microcavity nonlinear photonic devices such as microdisks, photonic crystals and metasurfaces. We demonstrate vdW microdisk resonators with quality (Q) factors exceeding 106. Such Q factors enable efficient continuous-wave nonlinear optical processes, including second-harmonic generation, sum-frequency generation and optical parametric amplification, with full free-spectral-range thermal tunability. These results position vdW materials as key material building blocks for next-generation integrated photonics and optoelectronics.