21 October 2016 Challenges and solutions for high performance SWIR lens design
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Abstract
Shortwave infrared (SWIR) cameras are becoming increasingly attractive due to the improving size, resolution and decreasing prices of InGaAs focal plane arrays (FPAs). The rapid development of competitively priced HD performance SWIR cameras has not been matched in SWIR imaging lenses with the result that the lens is now more likely to be the limiting factor in imaging quality than the FPA. Adapting existing lens designs from the visible region by re-coating for SWIR will improve total transmission but diminished image quality metrics such as MTF, and in particular large field angle performance such as vignetting, field curvature and distortion are serious consequences.

To meet this challenge original SWIR solutions are presented including a wide field of view fixed focal length lens for commercial machine vision (CMV) and a wide angle, small, lightweight defence lens and their relevant design considerations discussed. Issues restricting suitable glass types will be examined. The index and dispersion properties at SWIR wavelengths can differ significantly from their visible values resulting in unusual glass combinations when matching doublet elements. Materials chosen simultaneously allow athermalization of the design as well as containing matched CTEs in the elements of doublets.

Recently, thinned backside-illuminated InGaAs devices have made Vis.SWIR cameras viable. The SWIR band is sufficiently close to the visible that the same constituent materials can be used for AR coatings covering both bands. Keeping the lens short and mass low can easily result in high incidence angles which in turn complicates coating design, especially when extended beyond SWIR into the visible band. This paper also explores the potential performance of wideband Vis.SWIR AR coatings.
Conference Presentation
© (2016) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
M. C. Gardner, P. J. Rogers, M. F. Wilde, T. Cook, A. Shipton, "Challenges and solutions for high performance SWIR lens design", Proc. SPIE 9987, Electro-Optical and Infrared Systems: Technology and Applications XIII, 99870C (21 October 2016); doi: 10.1117/12.2241089; https://doi.org/10.1117/12.2241089
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