Terahertz quarter-wave plate based on subwavelength hole arrays

A compact quarter-wave plate (QWP) based on a doubly-periodic subwavelength hole array backed by a dielectric slab is designed analytically under perfect electric conductor (PEC) assumption and demonstrated its validity numerically for aluminum at terahertz (THz). The form birefringence is achieved by allowing the overlap of the TM (electric field polarized along the larger in-plane period) and TE (electric field polarized along the shorter in-plane period) extraordinary transmission resonances. Given the simplicity of the design, it holds promise for compact narrow-band polarizing devices.