Broadband Terahertz Polarization Converter and Asymmetric Transmission Based on Coupled Dielectric‐Metal Grating

Coupled dielectric‐metal gratings are investigated for broadband terahertz (THz) wave polarization conversion and asymmetric transmission by the experiments and numerical simulations, which are composed of the subwavelength Si grating and metallic wire grating layers. The dielectric grating layer with a large artificial birefringence and low dispersion is employed as a phase engineered waveplate, and the metal wire grating arranged with a 45° angle to the dielectric grating is utilized as a high‐efficiency polarizer. Due to the subwavelength integration, this coupled grating presents a local resonance coupling mechanism between dielectric and metal gratings, which greatly enhances the polarization rotation and expands the bandwidth, not a simple combination with dielectric and metallic gratings. The results demonstrate that a broadband asymmetric transmission with an extinction ratio of 30dB from 0.2 to 1.2 THz is achieved and the highest transmission of 90% can be obtained. It provides a simple way towards practical applications for THz artificial dispersion materials, polarization control and asymmetric transmission. Terahertz (THz) polarization converter has an irreplaceable role in manipulating the polarization states of THz waves. Here, a coupled dielectric‐metal grating is proposed for broadband THz wave polarization conversion and asymmetric transmission, which is composed of a subwavelength Si deep relief grating and gold wire grating on the two surfaces of a Si substrate. The results show that broadband asymmetric transmission is achieved with an extinction ratio of 30dB from 0.2 to 1.2 THz and the highest polarization conversion of 90% can be obtained.