Infrared detector size: how low should you go?

In the past five years, significant progress has been accomplished in the reduction of infrared detector pitch and detector size. Recently, longwave infrared detectors in limited quantities have been fabricated with a detector pitch of 5 micrometers. Detectors with 12 micrometer pitch are now becoming standard in both the midwave infrared (MWIR) and longwave infrared (LWIR) sensors. Persistent surveillance systems are pursuing 10 micrometer detector pitch in large format arrays. The fundamental question that most system designers and detector developers desire an answer to is: "how small can you produce an infrared detector and still provide value in performance?" If a system is mostly diffraction-limited, then developing a smaller detector is of limited benefit. If a detector is so small that it does not collect enough photons to produce a good image, then a smaller detector is not much benefit. Resolution and signal-tonoise are the primary characteristics of an imaging system that contribute to targeting, pilotage, search, and other human warfighting task performance. In this paper, we investigate the task of target discrimination range performance as a function of detector size/pitch. Results for LWIR and MWIR detectors are provided and depend on a large number of assumptions that are reasonable.