High-efficiency, large-area, topology-optimized metasurfaces

Abstract

Metasurfaces are ultrathin optical elements that are highly promising for constructing lightweight and compact optical systems. For their practical implementation, it is imperative to maximize the metasurface efficiency. Topology optimization provides a pathway for pushing the limits of metasurface efficiency; however, topology optimization methods have been limited to the design of microscale devices due to the extensive computational resources that are required. We introduce a new strategy for optimizing large-area metasurfaces in a computationally efficient manner. By stitching together individually optimized sections of the metasurface, we can reduce the computational complexity of the optimization from high-polynomial to linear. As a proof of concept, we design and experimentally demonstrate large-area, high-numerical-aperture silicon metasurface lenses with focusing efficiencies exceeding 90%. These concepts can be generalized to the design of multifunctional, broadband diffractive optical devices and will enable the implementation of large-area, high-performance metasurfaces in practical optical systems.

Metasurfaces: Bigger and better ways to manipulate light

A new strategy for designing and manufacturing ‘metasurfaces’ - surfaces patterned at scales below the wavelength of light - will allow wider exploration of their optical effects. The sub-wavelength patterning of ultra-thin metasurfaces manipulates electromagnetic waves, including visible light, for use in many applications including sophisticated optical systems, sensing applications and optical computing. Researchers in the USA and France, led by Jonathan Fan at Stanford University, devised a novel three-step process to optimally design, manufacture and then “stitch together” small metasurface sections to create larger scale structures. Previous size limitations due to the extensive computational resources required to design the surfaces were overcome by the step that combines smaller sections with optimized topology. The team demonstrated the power of their procedures by making large area silicon metasurfaces that can focus light with impressively high efficiency.