Tunable Multi-Functional Metamaterial Based on Photosensitive Silicon for Unidirectional Reflectionlessness, Polarization Conversion, and Asymmetric Transmission.

We propose a tunable multi-functional metamaterial composed of two pairs of gold corner resonators interconnected with photosensitive silicon, operating in the terahertz range. This design achieves dual-band unidirectional reflectionlessness, polarization conversion, and asymmetric transmission for linearly polarized waves, regardless of whether the photosensitive silicon is in the insulating or conductivity state. When the photosensitive silicon transitions from the insulating state to the conductivity state, its conductivity increases significantly, resulting in a frequency shift phenomenon in the functional peak frequencies. Numerical simulations demonstrate the structure's robust performance in dual-band unidirectional reflectionlessness and its significant asymmetric transmission, with minimal sensitivity to variations in the incident angle and photosensitive silicon sheet length. By integrating multiple functionalities and enabling frequency tunability through the control of photosensitive silicon conductivity, this design offers a reconfigurable solution for THz applications, such as switches, polarization converters, and modulators.