Verification of sensitivity enhancement of SWIR imager technology in advanced multispectral SWIR/VIS zoom cameras with constant and variable F-number

摘要

Current designs of combined VIS-color/SWIR camera optics use constant F-number over the full field of view (FOV) range. Especially in the SWIR, limited space for the camera integration in existing system volumes and relatively high pitch dimensions of 15μm or even 20μm force the use of relatively high F- numbers to accomplish narrow fields of view less than 2.0° with reasonable resolution for long range observation and targeting applications. Constant F-number designs are already reported and consideredfor submarine applications. The comparison of electro-optical performance was based on the given detector noise performance and sensitivity data by the detector manufacturer [1] and further modelling of the imaging chain within linear MTF system theory. The visible channel provides limited twilight capability at F/2.6 but in the SWIR the twilight capability is degraded due to the relatively high F-number of F/7 or F/5.25 for 20 urn and 15 μm pitch, respectively. Differences between prediction and experimental verification of sensitivity in terms of noise equivalent irradiance (NEI) and scenery based limiting illumination levels are shown for the visible and the SWIR spectral range. Within this context, currently developed improvements using optical zoom designs for the multispectral SWIR/VIS camera optics with continuously variable F-number are discussed, offering increased low light level capabilities at wide and medium fields of view while still enabling a NFOV ＜ 2° with superior long range targeting capabilities under limited atmospherical sight conditions at daytime.