Fresnel zone plate metalens using silicon subwavelength gratings

Metalenses have shown great promise in performing high-efficiency subwavelength focusing with wavelength-scale flat optical components. The majority of metalenses designed for telecommunication wavelengths, particularly at 1550 nm, utilize relatively tall amorphous silicon posts to form an array of scattering elements with phase control spanning the 0 to 2π range. In this work, we present the design of a binary phase Fresnel zone plate metalens in a silicon-on-insulator platform. The proposed metalens uses trapezoidally segmented subwavelength grating to form concentric rings to spatially vary the effective index across the device. Only one single etch step is required to achieve desired performance.