Terahertz non-reciprocal transmission in silicon photonic crystal metasurfaces with high-Q quasi-bound states

Non-reciprocal devices can be used to protect terahertz radiation sources and detectors from system echo reflection and noise interference. We propose an asymmetric groove silicon photonic crystal cylindrical metasurface, which generates high-<i>Q</i> quasi-bound states (q-BIC) and enhances nonlinearity. At terahertz wave incident intensity of 0.28 MW/cm², the isolation of the proposed structure reaches 34.28 dB. By studying the transition mechanism of nonlinear metasurfaces from BIC to q-BIC through multi-level decomposition and electromagnetic fields, the influence of structural parameters and terahertz wave incidence angle on achieving non-reciprocal transmission performance of terahertz waves is analyzed. The idea of designing non-reciprocal transmission devices using high-<i>Q</i> q-BIC metasurfaces can be extended to the microwave and optical wave regions.