Strong coupling and ultrafast switching in hybrid epsilon-near-zero-plasmonic metasurfaces

Nonlinear optical materials are crucial for ultrafast all-optical devices, yet traditional materials often exhibit weak nonlinearities and require long interaction lengths, limiting practical applications in high-speed optical systems. Epsilon-near-zero (ENZ) materials with unique linear and nonlinear optical behaviors have opened new avenues for enhancing light-matter interactions in such devices. However, achieving strong coupling and ultrafast switching in hybrid ENZ-plasmonic systems with threefold rotational symmetry remains unreported. This work designs a hybrid ENZ-plasmonic metasurface with periodic gold (Au) nanoarrays and indium tin oxide (ITO) film. We model the ENZ properties with the Drude model and characterize the nonlinear response via the two-temperature model. The proposed structure exhibits a notable Rabi splitting in the transmission spectra, with coupling strength g=0.23. Through changing structural parameters, it is revealed that the lower polariton is influenced by the ITO thickness, while the upper polariton is mainly controlled by the Au thickness. The electric field is significantly enhanced with a 90-fold increase and greatly confined in ENZ ITO. Additionally, the metasurface demonstrates an ultrafast nonlinear response, with a maximum nonlinear refractive index of 6.053cm²GW^-1 at 1566 nm, which is 10³ times greater than the single ITO film. The system achieves an all-optical response time of 222 fs, with dual-wavelength modulation depths of 5.275 dB and 8.417 dB at 1430 nm and 1532 nm, respectively. These results highlight the potential of the ENZ-plasmonic metasurface as an ultrafast all-optical switch, offering a promising platform for future advancements in integrated photonic circuits with applications in next-generation all-optical devices.