High-resolution QWIP thermal imager for AFV upgrade

Abstract

Following on the success of the BIRC clip on thermal imaging sight for the BILL Anti-Tank Missile System, which was in fact the world's first military QWIP based thermal imager, and which has been successfully delivered to the Swedish Army in serial quantities, several new QWIP-based products from FLIR Systems AB in Sweden are now under contract for defense customers worldwide. These include the new Forward Observation Systems for Norway and Sweden, Airborne Search & Rescue Systems, and a new clip on thermal imager for the Bofors RBS 70 Air Defense Missile System. The latest of these products is the development of a High Resolution QWIP Thermal Imager, LIRC, under contract for an upgrade of a number of Swedish CV9040C Armored Fighting Vehicles for Swedish Army International Operations. The paper will focus on the rationale behind the system selection, the development of the military qualified QWIP Thermal Imagers and the current status of the program. 1. BACKGROUND In 1998, what was then the Optronics Division of CelsiusTech Electronics (now part of FLIR Systems AB) was approached by Bofors Missiles (now part of Saab Bofors Dynamics AB) regarding a new clip on thermal imaging sight for the BILL2 Anti-Tank Missile system for a requirement from the Finnish National Defence Forces. The new thermal imager, although similar in concept to earlier built and delivered versions, needed an extended target identification range. With the changes in world politics and structures since the fall of the Iron Curtain and the experience from the Gulf War, customer requirements had changed from needing to be able to engage (recognize) a target at the maximum weapons range, to being able to identify the target at the same range, in order to avoid fratricidal events. An imminent trial period in Finland made a rapid development necessary. A quick investigation of possible solutions was performed. The most critical decision was to make a choice of which detector technology to use. Earlier clip on sights were built on first generation detectors using British TICM I common modules. Use of a second generation detector like the Sofradir 240x4 element arrays would require the development of a scanning mechanism, something that would likely consume to much time and also would in fact be a late start in the competition for second generation imagers. Instead another solution was sought. A third generation detector, a staring Focal Plane Array (FPA) would simplify the system design and also be an attractive solution with the prospect of being more modern than the competitors'. Finding a suitable FPA was not immediately obvious though. Being primarily developed for an Army application in Northern Europe the system should use the Long Wave Infrared (LWIR) wave band. Mid Wave Infrared (MWIR) was considered firstly too susceptible to the dust and smoke of the armored battlefield, and secondly not sensitive enough against very cold targets and backgrounds. Operation at -40° C (-40° F) was required in the RFQ. Of the available LWIR FPAs, Mercury Cadmium Telluride (MCT) was considered too expensive in larger formats and uncooled FPAs did not have sufficient performance to achieve the required range. Since the early 1990's, CelsiusTech Electronics (CTE) had been participating in a research project at the Industrial Microelectronic Center (IMC - now part of Acreo) in Sweden. The goal of the project was to develop a Swedish infrared FPA based on Quantum Well Infrared Photodetector (QWIP) technology with a patented two dimensional diffraction grating increasing the quantum efficiency. In 1998 this project had demonstrated successful imaging with good performance 1 and complete detector-cooler modules were built at FLIR Systems AB (formerly Agema) for a commercial thermography product, SC3000. An informal cooperation between CTE and FLIR had existed for many years since both companies shared a common origin (AGA) and were both located close to Stockholm. Use of the