  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.
