Metamaterial Fresnel zone plate for backward terahertz-wave parametric oscillator applications

Metamaterial-based Rayleigh-Wood Fresnel-zone-plate (FZP) thin-film lenses, utilizing planar diffractive technology with artificial structures and subwavelength thickness, offer a flexible and distinctive optical design platform for terahertz (THz) applications. In this study, we designed a metamaterial-based and polarization independent FZP thin-film lens that can focus a monochromatic THz beam at 305 GHz with a high transmittance of 80% and a focal length of 78.7 mm. It will be applied in an integrated backward THz-wave parametric oscillator (BW-TPO) system.