Particle swarm optimization of polymer-embedded broadband metasurface reflectors

Many single-layer dielectric metasurfaces studied today offer optimal performance by maximizing the refractive index contrast between a meta-atom and a background material, thereby increasing the field confinement and enhancing the optical resonance. Such architectures typically utilize high-index dielectric meta-atoms contrasted against an air background. Patterning can be done through deposition and growth of high-index materials or etching designs into a high-index layer. Unfortunately, such structures may be easily damaged, are susceptible to moisture accumulation, and cannot be readily incorporated into multilayer designs. To improve upon the mechanical and environmental stability of conventional dielectric-in-air metasurfaces, we show that dielectric metasurfaces in a solid host matrix can still achieve large enough resonances to exhibit high reflectance over a broad spectral band. Particle swarm optimization is used to discover different broadband reflector designs, each with different performance advantages including ultra-wide broadband reflectance and polarization independence. All designs exhibit a reflectance of R ≥ ~99% over the range of at least Δ λ / λ 0 ≥ ~20% centered at the wavelength λ 0 = 1.55 µm. Finally, a decoupled method approximation is employed to predict the spectral response for a multilayer stack of metasurfaces, but with the added benefit of a lower computational cost.