A compact 2048x1536 pixel infrared imager for long distance surveillance

The evolution of infrared imaging technology has always followed, from a distance, the evolution of the technology in the visible waveband with ever increasing resolutions and decreasing pixel pitch. With such evolution the cameras in the visible are smaller than ever and display high quality imaging. Nowadays the size of the pixels in the infrared is generally much larger than its counterpart in the visible. However, the ratio of the size of the pixel to the wavelength is much smaller in the infrared than in the visible with the consequence that the gain on the pixel size could be limited considering today's rules of design. In the infrared, the recent advent of large 1024 x 768 pixel focal plane arrays based on 17 um pixel for the 8 to 12 um waveband raises development challenges. Nevertheless, it was recently shown that sampling a scene at a frequency higher than the one corresponding to the pixel pitch is an efficient way of increasing the resolution of an image for given pixel size and FPA dimensions. Following this strategy a 2048 x 1536 pixel imager with integrated microscan was developed based on an uncooled bolometer FPA. Due to its very small 8.5 um efficient pixel pitch the imager offers very high resolution and large field-of-view (FOV) using a short 50 mm focal length. Furthermore, since the size of the FPA is maintained at a reasonable size and the pixel pitch is very small the optics is compact and lightweight and the level of aberrations at the larger angles of the FOV is kept to a minimum offering excellent imaging quality. Such a platform could thus be used for very compact surveillance system and remote sensing instrumentation. This paper reviews the optics developed to perform the microscanned acquisition, the acquisition electronics and presents examples of high-resolution imaging. Finally, comparison of imaging with and without microscan is provided illustrating the usefulness of the microscan system despite the fact that the efficient pixel pitch is very close to the lower limit of the 8 to 12 um infrared waveband.