Small detectors in infrared system design

Recent progress, in small infrared detector fabrication, has raised interest in determining the minimum useful detector size. We approach detector size analysis, from an imaging system point of view, with reasonable assumptions for future sensor design. The analysis is a simplified version of the target task performance model using the parameter Fλ/d for generalization. Our figure-of-merit is a system characteristic. The results are easy to use and yield minimum useful detector size of 2 μm for the mid-wave infrared region (MWIR) and 5 μm for the long-wave infrared region (LWIR) when coupled with an F/1 optical system under high signal-to-noise ratio conditions. Final size depends upon optical design difficulty, manufacturing constraints, noise equivalent differential temperature, and the operational scenario. For challenging signal-tonoise ratio conditions and more reasonable F/1.2 optics, a 3 μm MWIR detector and a 6 μm LWIR detector are recommended. There are many benefits to approaching these detector sizes with low F-number optics. They include lower cost detectors, no need for dual FOV or continuous zoom optics, and no need for dual F-number optics. Our approach provides the smallest volume and lowest weight sensor with maximum range performance. While this paper focuses on infrared design, our approach applies to all imaging sensors.