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Photo-excited switchable broadband linear polarization conversion via asymmetric transmission with complementary chiral metamaterial for terahertz waves

We present a photo-excited complementary chiral metamaterial (CCMM), which could realize a broadband dynamically switchable linear polarization conversion and asymmetric transmission (AT) effect for terahertz (THz) waves. The unit-cell structure of the photo-excited CCMM is composed of a bi-layer twisted complementary cut-wire (CCW) structure integrated with semiconductor photoconductive silicon (Si). The electric response of the photoconductive Si filled in the slot of the CCW structure can be tuned by the different pump optical power. The simulation results indicate that normal incident x(y)-polarization wave propagation along the -z (+z) axis direction pass through the CCMM without pump beam is converted into the y(x)-polarization wave, and the polarization conversion ratio (PCR) of over 90% and AT parameter of over 0.8 in the frequency range of 0.69-0.82 THz can be obtained. Furthermore, the broadband PCR and AT parameter can be tuned dynamically with the variation of Si conductivity by adjusting the pump power. Moreover, the surface current distributions of the unit-cell structure with different Si conductivity at the resonance frequency are discussed to illustrate its physics mechanism. Therefore, this work could offer a new platform for exploring dynamically tunable THz polarization controlling devices with photoconductive materials and have great prospects in various areas, such as terahertz imaging and wireless communication