# Controlling the sign of chromatic dispersion in diffractive optics with dielectric metasurfaces

## TL;DR

This paper demonstrates how dielectric metasurfaces can control the sign and magnitude of chromatic dispersion in diffractive optics, enabling new functionalities and increased bandwidth.

## Contribution

It introduces a method to alter the fundamental dispersion properties of diffractive optics using dielectric metasurfaces, including experimental demonstrations of various dispersion regimes.

## Key findings

- Achieved positive, zero, and hyper negative dispersion in diffractive gratings
- Demonstrated a focusing mirror with fivefold reduction in chromatic dispersion
- Extended the functional range of diffractive optical devices

## Abstract

Diffraction gratings disperse light in a rainbow of colors with the opposite order than refractive prisms, a phenomenon known as negative dispersion. While refractive dispersion can be controlled via material refractive index, diffractive dispersion is fundamentally an interference effect dictated by geometry. Here we show that this fundamental property can be altered using dielectric metasurfaces, and we experimentally demonstrate diffractive gratings and focusing mirrors with positive, zero, and hyper negative dispersion. These optical elements are implemented using a reflective metasurface composed of dielectric nano-posts that provide simultaneous control over phase and its wavelength derivative. In addition, as a first practical application, we demonstrate a focusing mirror that exhibits a five fold reduction in chromatic dispersion, and thus an almost three times increase in operation bandwidth compared to a regular diffractive element. This concept challenges the generally accepted dispersive properties of diffractive optical devices and extends their applications and functionalities.