Imaging Spectrometer Using Phi-Polynomial Freeform Surfaces
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Solution Overview
Problem
Current imaging spectrometers face limitations in achieving increased spectral range, spectral resolution, compactness, and field of view while maintaining low distortion and diffraction-limited performance, often requiring trade-offs that compromise other performance objectives.
Innovation Solution
The use of ϕ-polynomial freeform surfaces in reflective and diffractive optics, which are asymmetric and defined by Zernike polynomial terms or other mathematical forms, enhances performance by allowing spatial and spectral broadening while maintaining diffraction-limited performance over a wide field of view, and can be optimized using spectral full field display tools and Nodal Aberration Theory.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional spherical or aspheric surfaces are used in imaging spectrometers, then the optical system is easier to manufacture, but the spectral range, spectral resolution, and field of view are limited
Solution Approach 1:
The patent applies asymmetric freeform surfaces (φ-polynomial surfaces) to the reflective and diffractive optics, breaking the traditional rotational symmetry of spherical and aspheric surfaces. This asymmetry enables independent control of sagittal and tangential aberrations, allowing simultaneous optimization of spectral range, spectral resolution, and field of view without the constraints of conventional symmetric surfaces.
2Adaptability or versatility
If the spectral range and field of view are increased, then the imaging performance is improved, but the optical volume and package size increase
Solution Approach 1:
The patent introduces freeform surfaces that operate in an additional degree of freedom beyond conventional spherical and aspheric surfaces. By utilizing φ-polynomial representations with both radial and azimuthal dependencies, the design adds a dimensional aspect to surface control, enabling compact optimization of optical paths that reduce volume while maintaining expanded spectral and spatial coverage.
3Measurement precision
If the spectral resolution and spectral range are increased, then the imaging performance is improved, but the distortion increases
Solution Approach 1:
The patent applies local quality control through φ-polynomial freeform surfaces that allow different regions of the optical surfaces to have locally optimized properties. By independently controlling aberrations in different field regions and spectral bands through azimuthal polynomial terms, the system maintains low distortion across the entire field of view while achieving high spectral resolution and extended spectral range.
4Measurement precision
If new technologies such as volume phase holography, DMDs, and multispectral photodiodes are used, then specific performance objectives are improved, but tradeoffs are made that compromise other performance objectives
Solution Approach 1:
The patent fundamentally changes the surface parameter representation from conventional spherical/aspheric coefficients to φ-polynomial representations. This parameter change enables simultaneous optimization of multiple performance metrics (spectral range, spectral resolution, field of view, distortion) through a unified mathematical framework, avoiding the need for separate technological components that would introduce complexity and tradeoffs.
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
This approach enables imaging spectrometers to achieve a spectral étendue of at least 9 millimeter degrees, significantly increasing the imaged spectral bandwidth and slit length while reducing the optical volume, maintaining low distortion, and achieving diffraction-limited performance across the entire image field.
Implementation Method 1
the dispersion created by a diffraction grating relatively displaces images of the slit
Implementation Method 2
the dispersion created by a diffraction grating relatively displaces images of the slit in a second orthogonal dimension
Implementation Method 3
A primary reflective optic with optical power, a secondary reflective diffractive optic, and a tertiary reflective optic with optical power collectively image the entrance aperture onto the detector array
Data Source
AI summary
Expanded performance opportunities for imaging spectrometers are described using ϕ-polynomial freeform surfaces in reflective and diffractive optics. The imaging spectrometers are generally of a type that include an entrance aperture for admitting radiation over a range of wavelengths, a detector array, a primary reflective optic with optical power, a secondary reflective diffractive optic, and a tertiary reflective optic with optical power for collectively imaging the entrance aperture onto the detector array through a range of dispersed positions. One or more of the primary reflective optic, the secondary reflective diffractive optic, and the tertiary reflective optic can include a ϕ-polynomial optical surface with no axis of symmetry and represented by a function that depends on both a radial component and an azimuthal component.