Dual-band tunable terahertz linear dichroism metasurface based on photosensitive silicon

Metasurfaces, with their precise manipulation of electromagnetic waves, provide an ideal platform for realizing efficient terahertz linear dichroism (LD) devices. However, the existing LD metasurfaces primarily rely on fixed structures, making it difficult to achieve multi-band response and dynamic control, thereby limiting their application in complex scenarios. This article first proposes a dual-band terahertz LD metasurface composed of asymmetric double-opening square ring and double-opening circular ring. The results show that the device exhibits a LD value of 0.99 at 0.850 THz and 0.98 at 1.094 THz, demonstrating a significant LD effect. By systematically analyzing the influence of structural parameters on device performance, this study provides guidance for designing high-performance LD metasurfaces. More importantly, by embedding photosensitive silicon at specific positions in the unit structure, dynamic regulation of the LD effect is achieved through external optical excitation. The results demonstrate that under all-optical modulation, the LD amplitudes at the two frequency points achieve modulation depths of 98.1% and 95.7%, respectively. As the optical pumping power increases, a new resonant peak appears near 1.049 THz, with an LD value of 0.966. This phenomenon indicates that the device has the capability to switch between different frequencies, demonstrating excellent LD tuning performance. The proposed terahertz LD metasurface possesses dual-band response and dynamic tuning capabilities, holding promise for key applications in the fields such as biosensing, molecular orientation analysis, and terahertz communication.