Quad-band linear terahertz frequency conversion in time-varying metasurfaces

Abstract

In this Letter, a quad-band linear frequency conversion prototype is proposed and investigated in terahertz region based on a time-varying metasurface. The unit cell of the metasurface consists of four pairs of concentric split-ring resonators loaded with photoactive silicon. By changing the conductivity of photoactive silicon via optical pump, both static and time-varying metasurfaces are achieved and investigated. Numerical results show that the transmission spectrum of the static metasurface has four merged resonant frequencies at 0.49THz, 0.58THz, 0.71THz, 0.81THz respectively, and linear frequency conversion appears at these four frequencies under the modulation of time-varying metasurface. The conversion linearity is also verified by applying dual-band bandpass filters with different center frequency. The coefficients of determination are 0.98, 0.94, 0.87, 0.96 correspondingly. This prototype provides a new approach for realizing quad-band frequency conversion for ambient terahertz wave and has wide applications in terahertz imaging and communication systems.