Resolution Performance Improvements in Staring Imaging Systems Using Micro-Scanning and a Reticulated, Selectable Fill Factor InSb FPA

Abstract

As staring focal plane array (FPA) detectors continue to mature, FPA based IR imaging systems are available in more compact packages that are lighter and consume less power than first or second generation scanning IR sensor packages. However, standard IR analysis models indicate that staring FPA based cameras, while having excellent sensitivity, will have reduced resolution when compared to scanning systems with similar sized detector elements and optics. This apparent resolution limitation is created by the fixed sampling of the active pixel size native to staring FPA systems. Micro-scanning, a technique which moves the image in sub-pixel steps on the focal plane, can provide some over-sampling and reduce this limitation. Standard attempts at micro-scanning using 2-dimensional starring arrays with near 100% fill factor produce only marginal improvements in resolution in these systems. We will present here a new concept in micro-scanning using an InSb FPA with reticulated detector elements and active area masking to provide a well defined, selectable fill factor.A compact micro-scanned imaging system design that weighs less than 8 pounds and consumes less than 15 watts is presented here. MRTD (Minimum Resolvable Temperature Difference) analyses demonstrating a 2X improvement in resolution in both vertical and horizontal directions over non-micro-scanned systems has been measured, a performance level which micro-scanned systems with non-reticulated FPAs cannot approach. Test data from this system will also be presented including NETD and MRTD performance. INTRODUCTIONIn the last decade, Staring Focal Plan Array (FPA) based thermal imagers have shown a steady increase in performance -in resolution, sensitivity, compactness of package, low power and in overall picture quality. Yet, every increase in performance is absorbed by the system user with a demand for even greater performance in the next iteration of camera design. Today, most of the improved system performance comes with the need for larger arrays, larger substrates and larger dewar/cooler/array assemblies -at the cost of a more expensive array and a higher power cooler.In 1997, Cincinnati Electronics Corp. (CE) developed a compact, low-cost, general purpose, MWIR imager and demonstrated a significant improvement in most areas of system performance. Called the NightConqueror system, this compact, multipurpose thermal imaging sensor is capable of displaying images from many formats of focal plane array (FPA) detectors. The system can display images from high density 640 x 512 pixel FPAs, medium density 256 x 256 or 320 x 240 pixel FPAs, or one or two axis micro-scanned medium density FPAs.In 1998 CE designed and manufactured a front-side illuminated, 100% reticulated, low fill factor (25%), medium density (256 x 256) array FPA to demonstrate the resolution improvement possible with a properly implemented 2-axis dither system. A NightConqueror camera was used to implement the system design. This paper