Silicon Fresnel Zone Plate Metalens with Subwavelength Gratings

Metalenses are planar optical components that have demonstrated immense potential for integrated optics. In particular, they are capable of high-efficiency subwavelength focusing without the bulkiness of traditional lenses. Dielectric metalenses operating in the C-band typically employ relatively tall, amorphous silicon structures arranged in a periodic array. Phase control spanning from 0 to 2 pi is accessed by varying the geometry of these scattering structures. The full 2 pi phase range is necessary to impose a hyperbolic focusing phase profile, but this is difficult to achieve without custom fabrication practices. In this work, we propose a binary phase Fresnel zone plate metalens designed for the standard 500 nm silicon-on-insulator platform. Our design uses subwavelength gratings with trapezoidal segmentation to form concentric rings. The effective index of the grating is set with the duty cycle using a single full-etch step to form the binary phase profile of the zone plate. The metalens design can be easily tuned to achieve longer focal lengths at different wavelengths. It offers a simple platform for high-throughput wavelength-scale focusing elements in free-space optics, including for microscopy and medical imaging.

Automated summary

Metalenses are planar optical components that enable high-efficiency subwavelength focusing without the bulkiness of traditional lenses. In this work, a binary phase Fresnel zone plate metalens is proposed for the standard 500 nm silicon-on-insulator platform, using subwavelength gratings with trapezoidal segmentation to form concentric rings. The metalens design can be easily tuned to achieve longer focal lengths at different wavelengths, making it suitable for various applications in free-space optics.