Ge2Sb2Te5-based nanocavity metasurface for enhancement of third harmonic generation

The third-order nonlinear processes in nanophotonic devices may have great potentials for developing ultra-compact nonlinear optical sources, ultrafast optical switches and modulators, etc. It is known that the performance of the nonlinear nanophotonic devices strongly relies on the optical resonances and the selection of appropriate nonlinear materials. Here, we demonstrate that the third harmonic generations (THG) can be greatly enhanced at subwavelength scale by incorporating alpha-Ge2Sb2Te5 (alpha-GST) into the nanocavity metasurface. Under pumping of a near-infrared femtosecond laser, the THG from the nanocavity metasurface is similar to 50 times stronger than that from the bare GST planar film. In addition, the nanocavity metasurface also provides a powerful platform for characterizing the third-order nonlinear susceptibility of the active medium in the cavity. We expect that the GST-based nanocavity metasurface could open new routes for achieving high efficiency nonlinear nanophotonic devices.