| Abstract:Long-wavelength infrared imaging, while critical in applications such as terrestrial remote sensing, astronomy, etc., faces fundamental challenges from the overwhelming thermal background radiation. This background photon flux often pushes conventional detectors to the limits of their background-limited performance (BLIP), when the main limiting factor is not the intrinsic noise of the detector, but rather the bulk noise of the background itself. In this paper, we will argue for a key categorization that distinguishes between two superficially similar but fundamentally different detection architectures: the “Difference Detector” vs. the "Differential Detector.) There are detector applications and implementation pathways that dictate that the background photocurrent of a conventional Difference Detector sets a background-determined threshold for detectable signal differences, whereas a Differential Detector is a device that measures differences in target physical quantities directly at the level of physical perception, where only weak difference signals are integrated leading to very large cumulative sampling that can increase signal-to-noise ratios to unprecedented levels. In particular, the paper introduces the path of differential detection technology based on quantum well infrared detectors (QWIPs), which, with their extremely low dark current, precise electrical controllability, and endowed spectral selectivity, provide an ideal physical basis for realizing high-performance long-wave infrared differential detectors, and have already made significant progress in experiments. Finally, the use of Fisher Information (FI) and Cramer-Rao Bound (CRB) provides a rigorous theoretical support for differential detectors. |