In this paper, a team of researchers from Kent State University and MIT Lincoln Laboratory report on an important development in uncooled LWIR imager technology. The authors present an analysis of a novel LWIR imager scheme in which IR thermal sensors are separated from electrical read-out by means of liquid crystal transducers. In this concept, LWIR illumination from the scene is focused on the array of liquid crystal pixels. Upon absorption of IR radiation, the liquid crystal components heat up and change their optical properties. This change, in turn, is probed with visible light and detected by a readily available commercial imager, such as a CCD or CMOS camera. The authors propose a further improvement to the imager design by implementing a Fabry-Perot interferometer (étalon) structure to enhance optical probing of the liquid crystal pixel birefringence. The authors demonstrate through analytical and numerical modelling that an étalon leads to an order of magnitude improvement in sensitivity compared to direct probing of the liquid crystal layer.
The presented results indicate that the liquid crystal LWIR imager is a viable alternative to commonly used imagers based on micro-bolometers. Decoupling of IR sensor elements from the electronic readout allows excellent design flexibility, allowing tuning and optimization of each component individually. Furthermore, this work highlights the clear advantage of liquid crystal arrays in terms of scalability to large formats and suggests that further improvements in sensitivity are within reach.
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