A photoexcited broadband switchable metamaterial absorber with polarization-insensitive and wide-angle absorption for terahertz waves

We present a design and numerical study of a polarization-insensitive and wide-angle photoexcited broadband switchable metamaterial absorber (MMA) in the terahertz (THz) regime. The switchable MMA comprises a periodic array of dielectric substrate sandwiched with metallic four-splits-ring resonator (FSRR) structure and continuous metallic film. Filling the gap between the SRRs with a photoconductive semiconductor (silicon, Si), leading to easy modification of its electromagnetic (EM) response through a pump beam. The conductivity of photoconductive Si pads filled in the gap of SRRs can be tuned efficiently by external pump power. This results in the modulation of absorption magnitude with a modulation depth of 62.2%, and a broadband switch of absorption peak frequencies varying from 0.82 to 0.51 THz. Further numerical simulations demonstrate that the switchable MMA has the merit of polarization-insensitive and wide-angle absorption. The realization of broadband redshift tunable MMA offers opportunities to mature semiconductor technologies and potential applications in active THz modulator and switcher. (C) 2015 Elsevier B.V. All rights reserved.