Bifocal Fresnel lens based on the polarization-sensitive metasurface

Thin structured surfaces allow flexible control over the propagation of electromagnetic waves. Focusing and polarization state analysis are among functions, required for effective manipulation of radiation. Here, a polarization-sensitive Fresnel zone plate lens is proposed and experimentally demonstrated for gigahertz spectral range. Two spatially separated focal spots for orthogonal polarizations are obtained by designing metasurface pattern, made of overlapping tightly packed cross- and rod-shaped antennas with a strong polarization selectivity. The optimized subwavelength pattern allows multiplexing two different lenses with low polarization crosstalk on the same substrate and provides a control over focal spots of the lens only by changing the polarization state of the incident wave. More than a wavelength separation distance between the focal spots was demonstrated for a broad spectral range, covering half a decade in frequency. The proposed concept could be straightforwardly extended for terahertz and visible spectra, where polarization-sensitive elements utilize localized plasmon resonance phenomenon.