SWIR Multi-Conjugate Liquid Crystal Tunable Filter
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Solution Overview
Problem
Existing optical filters in the short-wave infrared range face challenges in achieving high transmission while maintaining an excellent out-of-band rejection ratio, and they often require long switching times and are costly for hyperspectral imaging applications.
Innovation Solution
A multi-conjugate liquid crystal tunable filter configuration is developed, utilizing serially arranged birefringent retarders and polarizers with varying thickness and rotational relationships, incorporating both fixed and tunable liquid crystal elements to achieve high finesse and fast switching speeds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple birefringent retarders and polarizing filters are used to improve wavelength discrimination, then the out-of-band rejection ratio is improved, but the transmission loss increases
Solution Approach 1:
The patent changes the physical parameters of the birefringent retarders by using materials with different birefringence values and varying thicknesses. This allows optimization of the filter stages to achieve high wavelength discrimination while minimizing transmission loss through precise parameter selection.
Solution Approach 2:
The patent employs composite material structures by combining multiple birefringent retarders with different material properties and polarizing filters in serial stages. This composite approach enables sophisticated wavelength discrimination while managing transmission characteristics through material selection and arrangement.
2Measurement precision
If a large number of filter stages are used to achieve high wavelength discrimination, then the out-of-band rejection ratio is improved, but the light energy transmission decreases
Solution Approach 1:
The patent applies local quality by assigning different characteristics to different filter stages - some stages use higher birefringence materials for strong discrimination, while others use lower birefringence materials to maintain transmission. This localized optimization across serial stages achieves high overall discrimination with acceptable transmission.
Solution Approach 2:
The patent introduces tunable liquid crystal elements that dynamically adjust the birefringence properties of retarders. This dynamic capability allows the filter to adapt its discrimination characteristics and transmission properties, optimizing performance for different wavelength selection requirements.
3Measurement precision
If traditional birefringent filters are used to achieve high finesse, then the wavelength discrimination is improved, but the switching time increases
Solution Approach 1:
The patent replaces mechanical adjustment mechanisms with electrically controlled liquid crystal elements. This substitution eliminates mechanical movement, enabling fast electronic tuning of the filter wavelengths while maintaining high finesse through precise control of the liquid crystal birefringence.
Solution Approach 2:
The patent employs dynamic liquid crystal materials that can rapidly change their optical properties when voltage is applied. This dynamic response enables fast switching between different wavelength selections while maintaining the high wavelength discrimination provided by the multi-stage birefringent structure.
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 filter achieves high transmission with excellent out-of-band rejection, fast tuning speeds, and cost-effectiveness, suitable for demanding spectral imaging applications like SWIR hyperspectral imaging.
Implementation Method 1
Birefringence is a characteristic of certain crystals wherein there is a difference in optical index for orthogonal light components that are aligned to the respective fast and slow axes of the crystal. If a plane polarized input light signal is aligned at 45° to the fast and slow axes a birefringent crystal, for example, the crystal induces a differential phase retardation between a component that is parallel to the slow axis versus the component that is parallel to the fast axis.
Implementation Method 2
A multi-conjugate liquid crystal tunable filter configuration is developed, utilizing serially arranged birefringent retarders and polarizers with varying thickness and rotational relationships, incorporating both fixed and tunable liquid crystal elements
Data Source
AI summary
A SWIR 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 850-1700 nm.