Photoexcited broadband redshift switch and strength modulation of terahertz metamaterial absorber

We demonstrate an optically implemented absorption modulation and redshift switch of metamaterial absorber at terahertz frequencies. Hybrid metal-semiconductor split ring resonators (SRRs) form the active structure, which can be tuned by applying an external pump power. This enables effective controls of the absorption strength and absorption peak frequency. As a function of incident pump power, the conductivity of silicon pads filled in the gap of SRRs is tuned efficiently, resulting in the modulation of absorption magnitude with a modulation depth of 60.5%, and a broadband switch of absorption peak frequencies varying from 1.11 to 0.87 THz. Multiple-reflection interference theory is used to analyze the reflection spectrum quantitatively under various silicon conductivities, and the results are in good agreement with full-wave simulations. The optical-tuned absorber demonstrates the viability to incorporate metamaterials to mature semiconductor technologies and has potential applications as an active terahertz modulator and switch.