Metasurfaces are arrays of subwavelength anisotropic light scatters (optical antennas) that can produce abrupt changes in the phase, amplitude or polarization of light. Within the last few years, significant progress has been made in the design of metasurfaces that refract and focus light, enabling many unique properties and applications such as holograms, optical vortex generation/detection, ultrathin focusing lens, perfect absorber, etc.

This tutorial will cover the fundamental principles, advanced designs and technological applications of optical metasurfaces, particularly focusing on the topics of (I) High Performance Metasurface Flat Optics—From Components to Systems, (II) Electrically Tunable Metamaterials and Metasurfaces for Control of Absorption, Emission and Scattering, (III) Optimization and Machine Learning for Nanophotonics, and (IV) Flat Optics for Dynamic Wavefront Manipulation and Mixed Reality Eyewear.

High-Performance Metasurface Flat Optics—From Components to Systems
Zhaoyi Li, Harvard University

Metasurfaces are leading to the emergence of new optical components that circumvent the limitations of standard refractive and diffractive optics by enabling dispersion engineering, which also leads to entirely new functionalities based on the local control of phase amplitude and polarization. Dispersion engineering has led to the demonstration of metalenses with correction of monochromatic aberrations and to achromatic metalenses and hybrid refractive/diffractive doublets across the visible spectrum. Inverse design is a  powerful method to design high-performance meta-optics. Its application to RGB metalenses for virtual reality will be presented.  Polarization optics and polarization-sensitive cameras without moving parts and conventional birefringent optics will be presented. The planarity of flat optics will lead to the unification of semiconductor manufacturing and lens-making; and recent industrial advances in this direction will be discussed.

Electrically Tunable Metamaterials and Metasurfaces for Control of Absorption, Emission and Scattering
Harry Atwater, California Institute of Technology

Progress in understanding resonant subwavelength optical structures has fueled a worldwide explosion of interest in both fundamental processes and nanophotonic devices for imaging, sensing, solar energy conversion and thermal radiation control. For most nanophotonic materials, the optical properties are encoded and fixed permanently into the nanoscale structure at the time of fabrication. Achieving electronic tunability of the optical properties is an emerging opportunity to bring metamaterials and metasurfaces to life as dynamic objects composed of tunable nanoscale resonators and antennas. Gated field effect tuning of the carrier density in conducting oxides and two-dimensional materials enables the optical dispersion of individual structures to be altered from dielectric to plasmonic, yielding active nano-antenna arrays with electrically tunable absorption, radiative emission and scattering properties.

Creating Metasurfaces and Metadevices with Mie Resonators Speaker
Jonathan Fan, Stanford University

Machine learning is revolutionizing the way photonic systems are being simulated and designed. In this tutorial, we will cover three concepts at the interface of machine learning and nanophotonics. First, we will discuss the use of discriminative networks as surrogate solvers and discuss their architectures, capabilities and limitations. Second, we will elucidate how generative networks can learn to output distributions of candidate layouts for device design. Third, we will cover global optimization methods that use the dataless training of generative networks to search for the global optimum in non-convex design spaces. Together with surrogate solvers, freeform optimization of nanophotonic devices can be performed four orders of magnitude faster than with conventional methods.

Flat Optics for Dynamic Wavefront Manipulation and Mixed Reality Eyewear
Mark Brongersma, Stanford University

Since the development of diffractive optical elements in the 1970s, major research efforts have focused on replacing bulky optical components with thinner, planar counterparts. The more recent advent of metasurfaces, i.e. nanostructured optical coatings, has further accelerated the development of flat optics through the realization that resonant optical antenna elements can be utilized to facilitate local control over the light scattering amplitude and phase.

In this presentation, I will start by showing how passive metasurfaces can start to impact augmented and virtual reality applications. I will discuss the creation of high-efficiency metasurfaces for optical combiners for near-eye displays, OLED displays and eye-tracking systems. I will also briefly highlight recent efforts in our group to realize electrically-tunable metasurfaces employing nanomechanics, tunable transparent oxides, microfluidics, phase change materials and atomically-thin semiconductors. Such elements are capable of active wavefront manipulation for optical beam steering and dynamic holography. The proposed optical elements can be fabricated by scalable fabrication technologies, opening the door to many commercial applications.