High-Performance and Incident Angle-Tunable Terahertz Sensing Assisted by Bound States in the Continuum

Terahertz (THz) sensing has been attracting interest due to its capabilities for biological fingerprint and medical identification. However, achieving angle-tunable ultrahigh figure-of-merit (FOM) of THz sensing remains challenging due to the difficulty in realizing tunable resonances with ultrahigh quality factors. Here, we design a series of THz sensors based on subwavelength metallic metagratings with compound lattices, enabling tunable ultrahigh FOM utilizing the physics of accidental bound states in the continuum (BICs). Under transverse-magnetic polarized electromagnetic wave illumination, the excited field of quasi-BIC is strongly localized within the grooves, leading to ultrahigh sensitivity (S) and FOM. The linewidths and frequencies of quasi-BICs are characterized alongside their sensing performance. A FOM of 109.62 is achieved when the incident angle is approximately equal to the BIC angle. Utilizing the tunability of accidental BIC, the BIC angle is tailored by adjusting the structure parameters. Corresponding BIC angle-dependent S and FOM are revealed. Although our study is only demonstrated through simulations, the robustness of the accidental BIC suggests potential for practical implementation of the design. Our work offers a high-performance sensing platform with high S and FOM, with great potential for various sensing applications.