Immersed Reflective Triplet Spectrometer for Compact Infrared Design
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Solution Overview
Problem
Conventional imaging spectrometers face challenges in achieving a balance between optical speed, size, and field of view while minimizing power consumption, especially for infrared applications, due to limitations with refractive optics such as chromatic aberration and the need for cryo-cooled components.
Innovation Solution
A monolithic reflective triplet imaging spectrometer design with an optical path immersed within a high-refractive index material, such as zinc selenide, which reduces the size and mass of the spectrometer while achieving faster optical speeds and larger fields of view, using a reflective triplet configuration with a diffraction grating and prisms to disperse and focus radiation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If refractive optics (lenses) are used in Dyson imaging spectrometer, then faster f/# and compact size are achieved, but chromatic aberration and limited spectral bandwidth occur
Solution Approach 1:
An immersion medium with refractive index n=2.4 is introduced between the optical components to increase the effective optical speed from f/2 to f/4.8 equivalent, allowing the all-reflective design to achieve performance previously only possible with refractive optics while maintaining wide spectral bandwidth
Solution Approach 2:
The refractive index parameter of the immersion medium is specifically selected as n=2.4 to achieve the desired optical speed enhancement, transforming the optical path length and effective f/# without requiring physical changes to the mirror geometry
2Reliability
If all-reflective optical designs (Offner-Chrisp) are used, then wide spectral bandwidth is achieved, but size is much larger and f/# faster than f/2 cannot be achieved
Solution Approach 1:
The immersion medium acts as an intermediary that increases the effective optical speed by factor of 2.4, allowing the all-reflective Offner-Chrisp design to achieve f/4.8 equivalent performance while maintaining compact size and wide spectral bandwidth
Solution Approach 2:
The optical path is folded back on itself within the monolithic body, with the dispersive element positioned to receive light after it has traversed the immersion medium, creating a nested configuration that reduces overall instrument size
3Reliability
If conventional Offner-Chrisp imaging spectrometer is used, then wide spectral bandwidth is achieved, but FOV is limited and size is much larger
Solution Approach 1:
The immersion medium increases effective optical speed, which directly enables larger field of view by reducing angular deviations and improving off-axis ray performance across the entire spectral bandwidth
4Volume of moving object
If refractive optics are used, then compact size for given f/# is achieved, but cryo-cooled imaging optics are required
Solution Approach 1:
Refractive lenses are replaced with reflective mirrors in an all-reflective Offner-Chrisp configuration, eliminating chromatic aberration and the need for cryogenic cooling while achieving equivalent or better performance through the immersion medium
Solution Approach 2:
The immersion medium with n=2.4 provides the optical speed enhancement previously requiring cryo-cooled refractive optics, but in an all-reflective configuration that operates at ambient temperature
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 design results in a significantly smaller and lighter spectrometer that requires less cooling power, maintaining equivalent performance metrics like wavefront error and spectral coverage, while accommodating a wider field of view and correcting for distortion and chromatic aberrations.
Implementation Method 1
three mirrored surfaces configured to form a reflective triplet having an optical path immersed within the immersion material, the reflective triplet configured to receive incident optical radiation from an entrance face of the monolithic spectrometer body component and reflect the incident optical radiation along the optical path
Implementation Method 2
a dispersive element configured to receive and disperse the incident optical radiation reflected from the reflective triplet to provide dispersed optical radiation
Implementation Method 3
the reflective triplet is further configured to receive the dispersed optical radiation from the dispersive element and to reflect the dispersed optical radiation along the optical path to an exit face of the monolithic spectrometer body component
Data Source
AI summary
According to certain examples a spectrometer module for use in an imaging spectrometer includes a monolithic spectrometer body component made of an immersion material and including three mirrored surfaces configured to form a reflective triplet having an optical path immersed within the immersion material, the reflective triplet configured to receive incident optical radiation from an entrance face of the monolithic spectrometer body component and reflect the incident optical radiation along the optical path, and a dispersive element configured to receive and disperse the incident optical radiation reflected from the reflective triplet to provide dispersed optical radiation. The reflective triplet is configured to receive the dispersed optical radiation from the dispersive element and to reflect the dispersed optical radiation along the optical path to an exit face of the monolithic spectrometer body component.