A tunable ultra-wideband cross-polarization conversion based on the band splicing technology

Abstract

A novel tunable terahertz metamaterials polarization converter (PC) is presented in this paper, whose operating band can be extended by the innovative band splicing technology (combine different PCs with different bands to make the bands splice together) and adjusted into a broadband absorber via adjusting the temperature. Four different units are combined to form a supercell and the phases can be matched through the phase compensation optimization technology. It is a noteworthy finding that the working band becomes wider significantly as the four different working bands join together by the band splicing technology. At the same time, under the action of vanadium dioxide (VO2), the amplitude of reflectance is regulated through the temperature field. The simulation results display that below the critical temperature of 341 K (68 °C), VO2 is treated as an insulator (σ = 20 S/m), the cross-polarization conversion (CPC) can be achieved in the frequency range of 0.91–1.67 THz, whose relative bandwidth (RB) reaches 58.9%. The operating band is expanded compared with four single small units with similar basic structure but different parameters, whose bands are 1.11–1.714 THz, 1.08–1.68 THz, 1.13–1.7 THz, and 1.024–1.608 THz with polarization conversion ratios (PCRs) above 0.9. At high temperature which exceeds the critical temperature, VO2 turns into metal (σ = 200,000 S/m) and the PC is switched into an ultra-broadband absorber with the operating band of 0.744–1.782 THz (the relative bandwidth (RB) of 82.1%), which is significantly different from that at low temperature. Without complex geometry, the reflected PC can broaden the bandwidth on the existing basis. Besides, this metamaterial structure builds a bridge between the polarization converter and the absorber by taking advantage of the non-contact control method, which strengthens the degree of freedom of the electromagnetic metamaterials that would further create a greatly fertile ground for their applications.