Design Of High Transmittance Liquid Crystal Filter And Polarization Modulation Study

Optical filter can be used to extract a certain width of spectral band from continuous spectrum,which is the core device of spectral imaging technology,optical communication technology,all-optical network and so on.The Liquid Crystal Tunable filter(LCTF)based on the electrically controlled birefringence effect of Liquid Crystal and the principle of polarization interference has the advantages of low driving voltage,easy to accurately adjust the filtering wavelength,low loss and easy integration.Therefore,this paper focuses on the major research work for improving the filtering performance of LCTF.Firstly,this paper introduces the filtering principle and the abvantages of the two typical filter,including Lyot type and Solc type.Based on the continuous elastomer theory of liquid crystal,the spatial distribution of liquid crystal molecular pointing vector under external electric field is established.Combined with Jones matrix method,the transmission model of LCTF filter under vertical light incidence is established,and the spectral transmittance curves of Lyot type and Solc type are simulated in theory;In view of the high wavelength selectivity of Lyot type filter,an optimization design method of Lyot type liquid crystal filter based on immune algorithm is proposed in this paper;Considering the filtering performance objectives of Lyot LCTF,including Free Spectrum Range(FSR),spectral resolution,cut-off region sidelobe suppression,we use a multi-objective artificial immune algorithm in order to optimize the phase delay ratio of Lyot LCTF to achieve the optimal voltage combination parameters under any liquid crystal device thickness,which can intelligent control of LCTF filter performance.In addition,combining the respective advantages of high spectral resolution of Lyot type and high transmittance of Solc type,the targeted optimization of sidelobe suppression of composite LCTF is realized.Secondly,aiming at the bottleneck problem of low transmittance of cascade Lyot LCTF,the polarization splitter prism(PBS)can realize the separation and converging coupling function of S and P polarized light.In this paper,a dual-channel high-permeability LCTF scheme based on PBS is innovatively proposed to optimize the structure of LCTF from the view of filtering principle,meanwhile,comparing the spectral transmittance effect and imaging effect under single and double channels,PBS dual-channel high-permeability LCTF can double the spectral transmittance of the system.Then,considering the actual spectral imaging to dynamic tuning characteristics,this paper put forward the overpressure drive in order to achieve the fast driving of liquid crystal,through the theoretical simulation and experimental test,analysis of the overvoltage of driving and driven by normal liquid crystal response time,the former can shorten the LCTF wavelength switching time,which lay the foundation for realizing high speed real-time LCTF filter dynamic tuning.Finally,combined with the liquid crystal flexible full polarization modulation technology of liquid crystal variable retarder(LCVR),a unique spectrum and polarization imaging system based on PBS dual-channel LCTF and dual-LCVR under pure liquid crystal regulation is proposed in this paper.Based on Muller matrix,the spectroscopy-polarization measurement principle of the system is described in detail,and the influence of fast axis azimuth of liquid crystal and phase delay deviation on the Stokes parameter error is analyzed.A static active dual-LCVR polarization modulation and imaging verification system based on the simulation of laser light source was built to verify the feasibility and accuracy of the polarization restoration algorithm.In addition,spectral,polarization and visible light images of different objects based on single-channel LCTF and dual-LCVR systems were acquired,and the characteristics of different images were quantitatively analyzed from image information entropy,mean gradient,spatial frequency,standard deviation,edge intensity and other image indicators.Combining the advantages of brightness of visible light image and detail of polarization degree image,an image fusion algorithm based on wavelet change under regional energy fusion rule is proposed to realize polarization fusion of visible light image,which enhances image contrast and improves image clarity,and is suitable for target recognition and detection under low visibility conditions.