Quasi‐BIC Intrinsic Chirality in Bi‐Layer All‐Silicon Terahertz Metamaterial with Asymmetrical Circular Polarization Transmission and Conversion

In this research, a bi-layer all-silicon terahertz metamaterial (BATM) is proposed with maximum narrowband intrinsic chirality by introducing one in-plane asymmetry parameter and one out-of-plane asymmetry parameter. By introducing an additional in-plane asymmetry, the usually equal intensities of cross-polarization components under left circular polarized (LCP) and right circular polarized (RCP) incident light will be broken, as one will be confined to ≈0.03 and another keeps higher than 0.10. Moreover, the banned cross-polarization intensity can be further suppressed to 10^-4 level by importing another in-plane asymmetry and optimizing out-of-plane asymmetry. The tailoring on asymmetry parameters also brings asymmetrical transmission properties. Besides, more quasi-BIC chiral modes can be stimulated by breaking the translational symmetry, and the chiral intensity of all these modes can be modulated by controlling the vertical distance between the two layers. Furthermore, BATM is potential to integrate with micro-electro-mechanical system (MEMS) to realize actively dynamic tuning in the chiral spectra. The narrowband asymmetrical chiral transmission and polarization conversion properties enable BATM to be promising for optical isolation, polarization controlling, chiral molecule sensing, encoding, and filtering applications.