Design-based optimization of stray-light performance in a multispectral single aperture VIS/SWIR 2-chip camera

SK. Shaid-Ur Rahman; Bertram Achtner; Martin Hübner

doi:10.1117/12.3013735

28 June 2024 Design-based optimization of stray-light performance in a multispectral single aperture VIS/SWIR 2-chip camera

SK. Shaid-Ur Rahman, Bertram Achtner, Martin Hübner

Author Affiliations +

Proceedings Volume PC13042, Advanced Optics for Imaging Applications: UV through LWIR IX; PC1304203 (2024) https://doi.org/10.1117/12.3013735
Event: SPIE Defense + Commercial Sensing, 2024, National Harbor, Maryland, United States

Abstract

In this report we describe the effect of the uncoated and the coated grinded lens edges on the imaging performance of a high performance short wave infrared (SWIR) imager inside a fully achromatized multispectral SWIR/VIS zoom camera. The experimental result of various black coatings for the lens edges to prevent stray light in the VIS-SWIR spectrum is presented. SWIR cameras show significant advantages for the long range observation under different weather conditions (e.g, haze, mist or fog) due to the reduction of wavelength-dependent scattering extinction. The design of such a SWIR imager in a combined visible (450nm to 900nm) and the SWIR spectral (900nm to 1700 nm) camera with a continuous optical zoom factor of 15x for a limited space and relatively high pixel pitch of 15μm force the use of relatively high F-numbers to achieve narrow fields of view less than 1.5° with a reasonable resolution is a great challenge. Particularly unwanted stray light inside the camera significantly degrades the imaging performance of the SWIR sensor. A good anti-reflection coating on the lens elements improves the ghost images. However, especial prevention techniques are required to reduce the flare stray light that typically arises from reflection or scattering from non-optical path surfaces e.g., mount surfaces or edge surfaces of lenses. The mechanical baffles or stops can reduce these stray lights but it requires precise design and cost. The most common approach to prevent the stray light from the edges of the optical elements is to apply a black coating on the grinded lens edges. The available coatings for edge blackening are typically optimized for VIS spectral range and their blackening effect is limited in the SWIR spectrum by Fresnel reflection due to the index of refraction mismatch at the glass boundary. Here we have applied the appropriate black coating on the selective lens edges based on simulation as well as experiments and demonstrated the improved stray light performance in the SWIR channel.

Conference Presentation

(2024) Published by SPIE. Downloading of the abstract is permitted for personal use only.

Citation Download Citation

SK. Shaid-Ur Rahman, Bertram Achtner, and Martin Hübner "Design-based optimization of stray-light performance in a multispectral single aperture VIS/SWIR 2-chip camera", Proc. SPIE PC13042, Advanced Optics for Imaging Applications: UV through LWIR IX, PC1304203 (28 June 2024); https://doi.org/10.1117/12.3013735

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