Athermal VNIR/SWIR Spectrometer Using Mangin Lens
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Solution Overview
Problem
Current VNIR/SWIR spectrometers are bulky, heavy, and require thermal adjustments, limiting their compactness and efficiency for hyperspectral imaging, especially in airborne platforms, due to their thermal sensitivity and lack of athermalization.
Innovation Solution
A compact and athermal VNIR/SWIR Dyson spectrometer design incorporating a Mangin lens, pupil lens, diffraction grating, beam splitter, and focal plane arrays, which uses a combination of partially reflective and refractive surfaces to achieve spectral separation and correction, maintaining spectral resolution and image quality across a wide temperature range without the need for thermal adjustments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional VNIR/SWIR spectrometers are used, then spectral imaging capability is achieved, but the system becomes bulky and heavy
Solution Approach 1:
The patent combines VNIR and SWIR spectral channels into a single spectrometer system using a shared optical path with a beam splitter that separates the two spectral ranges to different focal plane arrays. This merging of functions reduces the overall system size and weight compared to having separate spectrometers for each spectral range.
Solution Approach 2:
The Mangin lens serves multiple functions: it acts as both a collimating lens and a focusing element for different spectral ranges, and its partially reflective surface enables wavelength-dependent beam routing. This multi-functionality reduces the number of separate optical components needed, thereby reducing system weight.
2Measurement precision
If traditional VNIR/SWIR spectrometers are used, then spectral imaging capability is achieved, but the volume and packaging envelope increase
Solution Approach 1:
The patent employs a nested optical configuration where the diffraction grating is positioned within the focal plane array housing, and the beam splitter is integrated into the optical path between the Mangin lens and the focal plane arrays. This nesting of components minimizes the overall packaging envelope.
Solution Approach 2:
The patent uses a three-dimensional optical arrangement where light is folded back on itself using the Mangin lens and beam splitter configuration, allowing the optical path to fit within a compact volume by utilizing spatial dimensions efficiently rather than a linear arrangement.
3Measurement precision
If temperature sensitive spectrometers are used, then spectral measurements can be performed, but motor adjusting of focal plane array position is required
Solution Approach 1:
The patent achieves athermalization by carefully selecting optical materials with complementary thermal expansion coefficients and refractive index temperature dependencies. The optical design compensates for thermal effects through parameter optimization, eliminating the need for motorized adjustment mechanisms while maintaining spectral measurement accuracy across temperature variations.
4Measurement precision
If Dyson prism blocks are used, then spectral separation is achieved, but the system becomes heavy
Solution Approach 1:
The patent replaces heavy solid Dyson prism blocks with a lighter optical configuration using a beam splitter and Mangin lens to achieve spectral separation. This substitution of mechanical/prism-based separation with a reflective/refractive optical system reduces system weight while maintaining spectral separation capability.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution provides a compact, lightweight, and thermally stable VNIR/SWIR spectrometer with low F# and wide field of view, enabling accurate spectral-spatial modeling and classification of targets, while maintaining spectral resolution and reducing thermal defocus within the specified temperature range.
Implementation Method 1
the diffraction grating diffracts radiation in the SWIR spectrum in a first diffraction order and diffracts radiation in the VNIR spectrum in a second diffraction order
Implementation Method 2
the reflective part directs radiation onto the pupil lens
Implementation Method 3
the pupil lens directs the SWIR and the VNIR radiation onto the refractive part of the Mangin lens
Implementation Method 4
the beam splitter reflects the VNIR radiation onto the second field lens
Implementation Method 5
the beam splitter having a coating and transmits the SWIR radiation onto the first field lens
Data Source
AI summary
A Compact and Athermal VNIR/SWIR Spectrometer utilizes a slit, a Mangin lens, a pupil lens adjacent to the diffraction grating, corrector lenses, a beam splitter, field lenses and SWIR and VNIR FPAs. In examples, two corrector lenses are used. Some examples do not utilize field lenses and beam splitter, some examples utilize only the SWIR radiation spectrum. By balancing the powers of the optical elements and Abbe numbers of glasses as well as usage of aspheric surfaces combinations, a monochromatic and polychromatic aberrational correction is achieved; by balancing optical elements refractive indices change with temperature an athermalization is achieved. The overall length of the spectrometer does not exceed 4 inches, and in some examples it is 2.5 inches. A wide field of view and a low F number are obtained with an operating wavelength range from approximately 400 to 2350 nm. The spectrometer is particularly suited to airborne applications.