Controlling dispersion in multifunctional metasurfaces

Jared Sisler,Alexander Y. Zhu,Wei Ting Chen,Federico Capasso

doi:10.1063/1.5142637

Abstract

Metasurfaces can be designed to exhibit different functionalities with incident wavelength, polarization, or angles through appropriate choice and design of the constituent nanostructures. As a proof-of-concept, we design and simulate three multifunctional metalenses with vastly different focal lengths at blue and red wavelengths to show that the wavelength dependence of focal length shift can be engineered to exhibit achromatic, refractive, or diffractive behavior. In addition, we design a metalens capable of achromatically focusing an incident plane wave to a spot and a vortex at red and blue wavelengths, respectively. These metalenses are designed with coupled subwavelength-scale dielectric TiO2 nanostructures. Our method illustrates a more general design strategy for multifunctional metasurfaces by considering phase and group delay profiles with applications in imaging, spectroscopy, and wearable optical devices.

Highlights

Metasurfaces consist of subwavelength spaced nanostructures to achieve precise control over the phase, amplitude, and polarization of light.1,2 By tailoring the geometric shapes of these nanostructures, it has been demonstrated that a single metasurface can exhibit multiple distinct functions.3,4 For instance, it has recently been shown that a metasurface hologram can generate different images in reflection and transmission.5 A metasurface could exhibit polarization,6–11 wavelength,12–15 or incident angle-dependent functionality.16–20 This leads to numerous potential applications where information can be multiplexed with little to no increase in the spatial footprint of the device
The near-field wavefront was approximated by simulating each metalens element with periodic boundary conditions, such an approximation has been shown effective when numerical aperture (NA) is small
Since the group delay requirements for diffractive behavior are easier to match with our library, there was more freedom to fit the phase at 660 nm for Metalens 3, which resulted in a tighter focal spot and higher Strehl ratio

Summary

Introduction

Metasurfaces consist of subwavelength spaced nanostructures to achieve precise control over the phase, amplitude, and polarization of light.1,2 By tailoring the geometric shapes of these nanostructures, it has been demonstrated that a single metasurface can exhibit multiple distinct functions.3,4 For instance, it has recently been shown that a metasurface hologram can generate different images in reflection and transmission.5 A metasurface could exhibit polarization-,6–11 wavelength-,12–15 or incident angle-dependent functionality.16–20 This leads to numerous potential applications where information can be multiplexed with little to no increase in the spatial footprint of the device. In order to achieve devices with the dual functionalities described above, the individual nanostructures placed across the metalens must simultaneously exhibit two distinct phase and group delay profiles at the design wavelengths.

Results

Conclusion