Broadband terahertz quarter-wave plates via multipolar-interference-assisted all-dielectric metamaterials

All-dielectric metamaterials with multipolar Mie resonances are proposed and experimentally realized, which operate as a broadband terahertz quarter-wave plate. Composed of elliptically-shaped silicon pillar arrays, the proposed metamaterials support dipole and quadrupole resonance modes. The interferences among these modes could minimize reflection and maximize transmission. Both numerical and experimental results of the meta-device reveal close to unity transmission and 270 degrees phase delay between two orthogonal directions in a broadband, making the meta-device operate as a terahertz quarter-wave plate. Such multipolar-interference-assisted all-dielectric metamaterials promise a new paradigm for broadband low-loss terahertz devices.