Multi-Conjugate Liquid Crystal Tunable Filter for Hyperspectral Imaging
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Solution Overview
Problem
Existing optical bandpass filters that rely on birefringence struggle with achieving high spectral resolution and high transmission efficiency over the visible to infrared range, particularly in hyperspectral imaging applications, due to limitations in wavelength discrimination and light energy transmission.
Innovation Solution
A multi-conjugate optical filter configuration using serially arranged birefringent retarders and polarizers with tunable liquid crystal elements, where stages with different retardation values and rotational angles are coordinated to achieve high finesse and fast switching speeds, optimizing for both narrow bandpass and wide spectral range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple stages of birefringence filtering are used to improve wavelength discrimination, then spectral resolution is improved, but transmission efficiency deteriorates due to cumulative polarizer losses
Solution Approach 1:
The patent uses liquid crystal variable retarders (LCVRs) that can dynamically change their birefringence retardation in response to applied voltages. This allows the filter to be tuned to different wavelengths by electrically adjusting the retardation of each LCVR stage, enabling fast spectral tuning without mechanical movement while maintaining high transmission efficiency through optimized stage coordination.
Solution Approach 2:
The patent changes the operational parameters of the birefringent stages by applying different voltages to the LCVRs, which alters their retardation values. This allows dynamic adjustment of the filter's spectral characteristics, enabling the system to achieve high spectral resolution at specific wavelengths while minimizing transmission losses by optimizing the retardation parameters of each stage.
2Measurement precision
If the number of filter stages is increased to achieve narrow bandpass, then wavelength discrimination is improved, but the ratio of passed light energy decreases
Solution Approach 1:
The patent employs multiple LCVR stages with dynamic voltage control, allowing each stage to be independently tuned. This dynamic coordination enables the system to achieve narrow bandpass with high wavelength discrimination while optimizing the overall transmission by electrically adjusting the retardation of each stage to minimize cumulative losses, rather than using fixed mechanical adjustments.
Solution Approach 2:
The patent replaces mechanical tuning mechanisms with electrically controlled LCVRs. This substitution eliminates mechanical wear and allows for precise, rapid adjustment of the filter stages' retardation values, enabling the system to achieve narrow bandpass and high discrimination ratios while maintaining high light energy transmission through optimized electrical control of each stage.
3Device complexity
If birefringent crystals with high birefringence are used to reduce the number of stages, then device complexity is reduced, but manufacturing precision requirements increase
Solution Approach 1:
The patent uses liquid crystal variable retarders instead of fixed birefringent crystals, allowing the retardation to be dynamically adjusted via applied voltages. This eliminates the need for extremely precise mechanical control of crystal thickness during manufacturing, as the effective retardation can be tuned electrically. The system achieves high spectral resolution with fewer stages while maintaining relaxed manufacturing tolerances through this dynamic control mechanism.
4Device complexity
If fixed birefringent filters are used, then device complexity is reduced, but tuning speed deteriorates
Solution Approach 1:
The patent implements dynamically controllable LCVR stages that can rapidly change their retardation values in response to voltage changes. This allows the filter to be electronically tuned across different wavelengths at high speeds, replacing slow mechanical tuning mechanisms. The dynamic nature of the LCVRs enables fast spectral switching while maintaining a relatively simple overall device structure with coordinated stages.
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 high transmission efficiency with excellent out-of-band rejection ratio and fast tuning speed, enabling accurate spectral imaging from visible to infrared wavelengths, suitable for demanding applications like hyperspectral imaging and threat detection.
Implementation Method 1
birefringent retarders and polarizers with tunable liquid crystal elements
Implementation Method 2
tunable liquid crystal elements
Implementation Method 3
polarizers with tunable liquid crystal elements
Data Source
AI summary
A VIS-NIR hyperspectral imaging filter has serial stages along an optical signal path with angularly distributed birefringent retarders and polarizers. The retarders can include active retarders such as tunable liquid crystal birefringent elements, passive retarders such as fixed retarders, and/or combinations thereof. Distinctly different periodic transmission spectra are provided by different filter stages, each having multiple retarders, in particular with some stages having broad bandpass peaks at wide spectral spacing and other stages have very narrow closely spaced peaks. The respective spectra include at least one tunably selectable band at which the transmission spectra of the filter stages coincide, whereby the salutary narrow bandpass and wide spectral spacing ranges of different stages apply together, resulting in a high finesse wavelength filter suitable for spectral imaging. The filter may be configured to provide faster switching speed and increased angle of acceptance and may operate in the rage of approximately 400-1100 nm.