Broadband Polarization-Insensitive Metamaterial Perfect Absorbers Using Topology Optimization

• Published in: IEEE photonics journal 2016-10, Vol.8 (5), p.1-11
• Main Authors: Sze Ming Fu, Yan Kai Zhong, Nyan Ping Ju, Ming-Hsiang Tu, Bo-Ruei Chen, Lin, Albert
• Format: Article
• Language: English
• Subjects: Absorption; Broadband communication; Diffractive optics; Genetic algorithms; Hidden Markov models; metamaterials; Optimization; Photonics; photovoltaic; plasmonics; silicon nanophotonics; Topology
• ISSN: 1943-0655; 1943-0647
• DOI: 10.1109/JPHOT.2016.2602335

A novel scheme for a perfect hyperbolic metamaterial (HMM) absorber is proposed, and experimental verification is provided. It has been shown previously that tapered HMM stacks can provide adiabatic waveguiding over a wide spectral range and thus are an ideal opaque absorber. Here, nontapered shape-optimized HMM absorbers are proposed, which facilitates the fabrication and promotes the large-area applications such as thermophotovoltaics (TPV). In the synthesis of the optimal patterns, we use 5-harmonic rigorously coupled wave analysis (RCWA) and experimental trials to shorten the trial-and-error time. The best pattern provides an averaged broadband experimental absorption of 88.38% over λ = 1 μm to λ = 2 μm, which is comparable to the state-of-the-art experimental effort using tapered HMM. The nontapered nature can be easier to fabricate from the semiconductor processing viewpoint. The physics behind the pattern-optimized HMM cavity is the broadband light coupling by the air-cavity and the unbounded photonic density of the states (PDOS) associated with the HMM. The topology optimized air cavity effectively couples the incident photons into the metal-dielectric stacking, eliminating the need of sidewall tapers. We believe the proposed topology-optimization methodology benefits the future design of compact metamaterial perfect absorbers (MPA), sensors, antenna, and thermophotovoltaic emitters, and absorbers.