Gradient Index Rod Lenses for Large Field Curvature Correction
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Solution Overview
Problem
Conventional field flattening technologies are inadequate for correcting large field curvatures in hyperspectral sensors and ultra-wide field imagers, leading to field-dependent defocus, spectral resolution blur, and spectral coordinate distortion due to the mismatch between curved focal planes and planar detector arrays.
Innovation Solution
The use of gradient index rod lenses, which are dielectric cylinders with a parabolic or complex radial variation of refractive index, to image the focal locus onto a planar detector array with unity magnification and no inversion, bridging the gap between curved focal loci and planar detectors, and optimizing performance through varying lengths, widths, and chromatic aberration compensation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional field flatteners (Piazzi-Smyth type) are used, then field curvature is reduced in typical lens systems, but they cannot correct large field curvatures generated by dispersive elements in hyperspectral applications
Solution Approach 1:
The field flattener is divided into multiple discrete gradient index rods arranged in an array, where each rod independently corrects field curvature for its local region. This segmentation allows the system to handle large field curvatures that would be impossible to correct with a single conventional field flattener element.
Solution Approach 2:
The patent employs gradient index rods with varying refractive index profiles (parameter change) to correct field curvature. By controlling the gradient parameter of each rod, the system can adapt to different field curvature conditions across the detector array, enabling correction of large field curvatures in hyperspectral applications.
2Reliability
If a negative field lens is placed adjacent to the image plane (Piazzi-Smyth technique), then field curvature is corrected in conventional systems, but it cannot compensate for large field curvatures from dispersive elements
Solution Approach 1:
The patent replaces the conventional mechanical field lens approach with gradient index rods that utilize refractive index gradients to correct field curvature. This substitution allows for more effective correction of large field curvatures while maintaining compatibility with planar detector arrays through the rods' ability to map curved focal loci directly onto the flat detector surface.
Solution Approach 2:
The gradient index rods introduce a new dimensional approach to field curvature correction by utilizing the refractive index gradient as an additional degree of freedom. This allows the system to correct field curvature in the optical path while maintaining a planar detector geometry, effectively bridging the gap between curved focal surfaces and flat detectors.
3Adaptability or versatility
If dispersive elements are used in hyperspectral sensors, then spectral dispersion is achieved, but strongly curved focal loci are produced that mismatch with planar detector arrays
Solution Approach 1:
The gradient index rods serve as an intermediary element between the dispersive element's curved focal locus and the planar detector array. Each rod acts as a local transformer that maps the curved field geometry to the flat detector surface, preserving spectral information while correcting the geometric mismatch.
Solution Approach 2:
The patent applies local quality by assigning different gradient index rod characteristics to different regions of the detector array. Each rod is optimized for its specific local field curvature condition, allowing precise correction of spectral coordinates across the entire field while maintaining the dispersive element's 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 gradient index rod lenses provide continuous high-resolution imaging, reduced coupling loss, and no cladding region dead space, effectively correcting large field curvatures and spectral distortions, allowing for improved spectral resolution and reduced detector array size requirements.
Implementation Method 1
dielectric cylinders with a parabolic or complex radial variation of refractive index, to image a focal locus of the received electromagnetic radiation onto a focal locus of an image surface
Data Source
AI summary
Field flatteners that can correct large field curvatures.