Terahertz polarization mode conversion in compound metasurface

A compound metasurface for terahertz (THz) wave polarization mode conversion has been experimentally investigated, which is integrated with an H-shaped metallic metamaterial and 45° arranged subwavelength dielectric grating on the two surfaces of a Si substrate. The polarization mode conversion from a TM to a TE resonance mode is achieved at 1.3 THz for forward transmission and 0.63 THz for backward transmission. Based on this property, a unidirectional transmission is obtained with the highest extinction of 23 dB at 0.63 THz. Moreover, due to the multiple reflections and subwavelength integration, a localized resonance mechanism in this metasurface greatly enhances the polarization conversion rate, reduces the insertion loss, and expands the operating bandwidth from 0.3 to 1.6 THz, not merely at the π phase matching point, which are quite different with the properties of the discrete metallic metamaterial and dielectric grating. This work provides an efficient way towards practical applications in THz broadband polarization conversion, polarization resonance mode manipulation, and unidirectional transmission.