Dielectric-resonator metasurfaces for broadband terahertz quarter- and half-wave mirrors

Abstract

Polarization conversion of terahertz waves is important for applications in imaging and communications. Conventional wave plates used for polarization conversion are inherently bulky and operate at discrete wavelengths. As a substitute, we employ reflective metasurfaces composed of subwavelength resonators to obtain similar functionality but with enhanced performance. More specifically, we demonstrate low-order dielectric resonators in place of commonly used planar metallic resonators to achieve high radiation efficiencies. As a demonstration of the concept, we present firstly, a quarter-wave mirror that converts 45° incident linearly polarized waves into circularly polarized waves. Next, we present a half-wave mirror that preserves the handedness of circularly polarized waves upon reflection, and in addition, rotates linearly polarized waves by 90° upon reflection. Both metasurfaces operate with high efficiency over a measurable relative bandwidth of 49% for the quarter-wave mirror and 53% for the half-wave mirror. This broadband and high efficiency capabilities of our metasurfaces will allow to leverage maximum benefits from a vast terahertz bandwidth.

Dielectrics for Terahertz Metasurfaces: Material Selection and Fabrication Techniques

“…Subwavelength structures composed of dielectric materials have been engineered for device‐specific applications at the terahertz regime. On one hand, low‐loss dielectric materials with moderate‐to‐high relative permittivity have been engineered into metasurfaces as phasing elements with nonuniform dimensions for wavefront manipulation and dynamic beam control for antennas and lenses or with anisotropic properties for polarization manipulation . On the other hand, lossy dielectric materials with moderately high relative permittivity are engineered to enhance coupling between and field confinement within subwavelength resonant cavity bodies.…”

“…In this way, the fundamental frequency of resonance and the device efficiency, are dependent on the resonator structure and dielectric material used. As a result, dielectric resonators made of different materials have been designed in different shapes to interact differently to the two orthogonal polarizations of an incident wave for linear to linear polarization rotation, linear to circular, and circular to circular polarization conversion with preserved handedness . Irrespective of the mode of operation (reflective or transmissive) the materials used are designed to exhibit low dissipation and high radiation losses for efficient output or conversion, as discussed earlier.…”

High‐efficiency cross and linear‐to‐circular polarization converters based on novel frequency selective surfaces

“…[4][5][6][7] Generally, reflection polarization converters have the higher efficiency and better bandwidth. [2][3][4][8][9][10][11][12] However, the transmission ones, which are more desirable in practical applications, suffer from either narrower bandwidth or lower transmission-efficiency 13,14 especially for the thin crosspolarization converters.…”

“…Recently developed metamaterials and metasurfaces 17,18 which exhibit exotic EM properties not found in nature, have attracted significant interest in the development of polarization converters, [19][20][21][22][23][24] resulting in numerous reflective and transmissive polarization converters with much reduced thicknesses. The recent developments aim at the realization of both the wide polarization conversion bandwidth and the high polarization conversion ratio (PCR), such as the microwave reflective metasurfaces, [2][3][4] gold helix structures in optics, 17 the planar ultrathin plasmonic metasurfaces at THz frequency, 11,[19][20][21][22] and other approaches. [8][9][10][11][12][13][14][23][24][25][26][27][28][29] In addition, anisotropic frequency-selective surfaces (FSSs) 30,31 have been applied to convert linear polarization into circular polarization (LP-CP) in the microwave regime.…”

“…The recent developments aim at the realization of both the wide polarization conversion bandwidth and the high polarization conversion ratio (PCR), such as the microwave reflective metasurfaces, [2][3][4] gold helix structures in optics, 17 the planar ultrathin plasmonic metasurfaces at THz frequency, 11,[19][20][21][22] and other approaches. [8][9][10][11][12][13][14][23][24][25][26][27][28][29] In addition, anisotropic frequency-selective surfaces (FSSs) 30,31 have been applied to convert linear polarization into circular polarization (LP-CP) in the microwave regime. Compared to transmissive polarization converters, the reflective ones are relatively easier to realize broadband and high-efficiency performance with smaller thicknesses.…”