Narrowband Perfect Absorber using Metamaterials

We propose a metamaterial-enhanced microbolometer with strong absorption over a narrow band that is dynamically tunable over the 8-10 micron band. A single-layer photonic metamaterial consisting of a thin metal film perforated with a 2-D array of dielectric apertures will be deposited on an amorphous-Silicon layer acting as an absorber and bolometer. The metamaterial, in conjunction with planar dielectric layers below the absorber, will trap and concentrate a narrow frequency band within the absorbing layer while strongly reflecting out-of-band light. This design is based on a previously developed metamaterial-enhanced Si photodiode that exhibited strong absorption over a narrow width (1% of the central frequency). Tuning the absorption band across the 8-10 micron range may be achieved via MEMS actuation applied to a standard air-bridge microbolometer structure. The metamaterial may be fabricated with standard photolithography, as we have demonstrated previously, and the rest of the fabrication involves materials and processes that are standard for microbolometers. We believe this structure offers considerable advantages over a multi-layer coupled split-ring and cut wire perfect absorber approach, including: ease of fabrication due to a single-layer metamaterial, scaling up an existing design rather than scaling down, and ease of integration with existing focalplane array microbolometers.