Abstract-MEMS terahertz-to-infrared band converter using frequency selective planar metamaterial

Fabio Alves, Leroy Pimental, Dragoslav Grbovic,  Gamani Karunasiri

Terahertz to infrared imaging system concept. Schematic diagram of the imaging system from the illumination source (left) to the infrared camera (right). The transmissivity, absorptivity and emissivity of the components are represented by the Greek letters τ, η and ε with the appropriate indices. The THz-to-IR FPA is placed inside a vacuum chamber with a THz-transparent window (receiving side) and a IR-transparent window (emitting side). The THz pixel area is represented by A0 while the IR camera optical aperture area is represented by A1. The object is depicted as an envelope with a concealed metallic key inside, showing in the THz image. Each THz pixel (dark square on the THz FPA) is mapped on a subarray of pixels on the IR camera FPA (follow the dashed red line).

https://www.nature.com/articles/s41598-018-30858-z


A MEMS terahertz-to-infrared converter has been developed based on the unique properties of metamaterials that allow for selective control of the absorptivity and emissivity of the sensors. The converter consists of a sensing element structurally made of planar metamaterial membranes, connected to a substrate frame by four symmetrically-located thermal insulators. Upon THz absorption, the temperature of the sensing element increases and the outward infrared flux from the backside of the element is read by a commercial long-wave infrared camera. Two configurations were designed and fabricated with metamaterial absorptivity optimized for 3.8 THz and 4.75 THz quantum cascade lasers. The first sensor, fabricated with an oxidized aluminum backside, exhibits higher responsivity, but lower conversion efficiency than the second sensor, fabricated with a metamaterial backside. The spectral characteristics of the metamaterial on the two sides can be optimized to improve both responsivity and sensitivity, while keeping the sensors’ thermal time constant sufficiently small for real time imaging. No dedicated electronics or optics are required for readout making metamaterial-based MEMS THz-to-IR converters very attractive for THz imaging as means of a simple attachment to commercial IR cameras.