"Quantum well infrared photodetectors (QWIP) are by design inherently suited for polarization sensitive imaging. The detection principle in regular QWIPs relies on etched 2-D gratings to couple the light to the quantum wells for absorption. By replacing the 2D gratings with 1D (lamellar) gratings polarization sensitivity is added to the thermal detection.
Thermal imaging is a great way to detect objects, but it requires the objects to be of different temperature or to have different emissivity than the background. Polarization detection further extends the possibility to differentiate between objects that have the same temperature but consist of different materials, since infrared polarized light can be generated by reflection or emission of radiation from planar surfaces. This allows for detecting objects that are previously undetectable by an infrared detector since they may be covered under a canvas or they may have a low thermal signature like an UAV."
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