Abstract
Wide field of view (WFOV) imaging systems can suffer from significant variations in performance from the center of the focal plane array (FPA) to the periphery of the detector. Some of these undesirable spatial variations include angle of incidence (AOI) of the marginal rays, illumination, and resolution non-uniformities. Optical designers are often required to go to great lengths to achieve adequate performance across the entire field of view, but these designs commonly possess high angles of incidence on optical surfaces and filters.
For optical coatings and bandpass filters, large AOIs have crucial implications for system performance, as the physics of optical interference bandpass filters requires that the band edges shift to shorter wavelengths as the optical AOI grows, and these spectral shifts with angle can be dramatic. A typical optical bandpass filter on a flat optical window will result in mission performance varying from the center to the extremes of the field of view in WFOV systems. These challenges are exacerbated in short-wave IR (SWIR) and mid-wave IR (MWIR) applications where typical requirements call for narrow, sharp-edged performance. In summary, the physics of the filters will define and inform the telescope designs.
Depending on the telescope design and bandpass coatings employed, the spectral response can range considerably across the FOV unless deliberately addressed. In this paper we will: 1) discuss bandpass spectral performance and optimization for variable AOI, 2) show how these coatings inform the optical design constraints for uniform FOV performance, 3) demonstrate how careful telescope design can limit the burden of high AOIs on filter surfaces in an optical system. These combined efforts inform the technical community of the trade space between compact telescope design and bandpass filter capabilities in WFOV systems.
Approved for public release. OTR 2022-00548.
Filter Design for Precise Spectral Performance in Wide-Field-of-View Optical Systems
Wide field of view (WFOV) imaging systems can suffer from significant variations in performance from the center of the focal plane array (FPA) to the periphery of the detector. Some of these undesirable spatial variations include angle of incidence (AOI) of the marginal rays, illumination, and resolution non-uniformities. Optical designers are often required to go to great lengths to achieve adequate performance across the entire field of view, but these designs commonly possess high angles of incidence on optical surfaces and filters.
For optical coatings and bandpass filters, large AOIs have crucial implications for system performance, as the physics of optical interference bandpass filters requires that the band edges shift to shorter wavelengths as the optical AOI grows, and these spectral shifts with angle can be dramatic. A typical optical bandpass filter on a flat optical window will result in mission performance varying from the center to the extremes of the field of view in WFOV systems. These challenges are exacerbated in short-wave IR (SWIR) and mid-wave IR (MWIR) applications where typical requirements call for narrow, sharp-edged performance. In summary, the physics of the filters will define and inform the telescope designs.
Depending on the telescope design and bandpass coatings employed, the spectral response can range considerably across the FOV unless deliberately addressed. In this paper we will: 1) discuss bandpass spectral performance and optimization for variable AOI, 2) show how these coatings inform the optical design constraints for uniform FOV performance, 3) demonstrate how careful telescope design can limit the burden of high AOIs on filter surfaces in an optical system. These combined efforts inform the technical community of the trade space between compact telescope design and bandpass filter capabilities in WFOV systems.
Approved for public release. OTR 2022-00548.