Direct thermal infrared vision via nanophotonic detector design

Abstract

Detection of infrared (IR) photons in a room-temperature IR camera is carried out by a two-dimensional array of microbolometer pixels which exhibit temperature-sensitive resistivity. When IR light coming from the far-field is focused onto this array, microbolometer pixels are heated up in proportion to the temperatures of the far-field objects. The resulting resistivity change of each pixel is measured via on-chip electronic readout circuit followed by analog to digital (A/D) conversion, image processing, and presentation of the final IR image on a separate information display screen. In this work, we introduce a new nanophotonic detector as a minimalist alternative to microbolometer such that the final IR image can be presented without using the components required for A/D conversion, image processing and display. In our design, the detector array is illuminated with visible laser light and the reflected light itself carries the IR image which can be directly viewed. We realize and numerically demonstrate this functionality using a resonant waveguide grating structure made of typical materials such as silicon carbide, silicon nitride, and silica for which lithography techniques are well-developed. We clarify the requirements to tackle the issues of fabrication nonuniformities and temperature drifts in the detector array. We envision a potential near-eye display device for IR vision based on timely use of diffractive optical waveguides in augmented reality headsets and tunable visible laser sources. Our work indicates a way to achieve direct thermal IR vision for suitable use cases with lower cost, smaller form factor, and reduced power consumption compared to the existing thermal IR cameras.