Study On The Method Of Polarized Plenoptic Imaging Based On Liquid Crystal Microlens Array

Generally,optical imaging detection presents an ability of efficiently recording featured information of targets,for example,texture,surface structure,spatial position,motion and posture,through capturing lightwaves emitted from objects,and are widely utilized in various application fields such as daily life,industrial measurement,medical diagnosis and machine vision.The factors of typical glaring,scattering and uneven refractive index distribution of circumstance mediums,will result in problems of narrowing imaging dynamic range,pattern blur or wavefront aberration.The multi-dimensional optical information such as wave-vector,polarization,wavefront and spectrum,can be used to guide the imaging technique development.Generally,liquid-crystal(LC)materials exhibit optical anisotropy,and thus can be used to effectively regulate the key parameters of incident beams including the phase,the polarization and the energy flux through applying electromagnetic field over them,so as to lay a technical basis for realizing multi-functional imaging detection.In this thesis,several functionalized LC electro-optical devices are developed according to standard microelectronic technology,and further introduced into the imaging detection microstructures.The integrated light-field and traditional planar polarization imaging detection architecture for sensing complicated targets and circumstance and the evaluation methods are constructed,respectively.The main works of this dissertation are as follows:Firstly,an electrically tunable polarization light-field imaging method based on LC device is proposed.The polarization regulating characteristics of near-field and far-field lightwaves incident upon the focal plane and processed by the sub-wavelength metal grating arrays are analyzed.Combined with the twisted nematic field effect of LC materials,an imaging detection model is established,and then the methods for performing operations of digital refocusing,depth estimation and depth resolution,are given,so as to lay a theoretical basis for guiding the imaging system construction and pattern post processing.The key fabricating process and the measurement methods and the testing platform are demonstrated.Secondly,a polarized light-field imaging technique based on stacked liquid-crystal microlens arrays(LCMLAs)is proposed.The focusing performances of incident beams with arbitrary polarization and the polarization-sensitive and insensitive point compressing plenoptic patterns are analyzed.According to the normalized point spread function(PSF)evaluation,the beam utilization efficiency in the polarization-insensitive mode compared with the polarization-sensitive LCMLA is more than 90%.An electrically tunable plenoptic camera based on stacked LCMLAs can be effectively operated in polarization-sensitive or insensitive mode.By electrically adjusting the stacked LCMLA,the orthogonally polarized light-field images and further the fused polarization-insensitive light-field images can be obtained effectively.Thirdly,a device-oriented twisted nematic liquid-crystal microlens array(TN-LCMLA)is proposed.According to the twisted nematic effect of LC materials,the polarization state of incident lightwaves can be modulated flexibly.The PSFs of orthogonally polarized incident beams can be obtained and the scanning manipulation of the polarization state of incident lightwaves performed efficiently.The stray light distribution introduced by the polarization sensitivity of LC materials can be effectively eliminated.A prototype of 3D polarization imaging detection camera based on the TN-LCMLA is constructed.The conventional planar(2D)and the polarization and light-field(3D)images of targets are obtained easily,and an experimentally verified polarization differential dehazing algorithm is proposed.Fourthly,a graphene anchoring LC molecule technology are presented.Based on the single-sided induced directional alignment in a micro-cavity,the LC molecules are rearranged orderly on the surface of a single crystal graphene(SCG)film with zigzag lattice direction.A large area single crystal graphene is prepared by the SCG growth method,and the SCG-LCMLA is fabricated,and then the spectral optics properties of the SCG-LCMLA in the visible and near infrared range are obtained.A compressed light-field imaging architecture by integrating a SCG-LCMLA and an arrayed photodetector is constructed,and thus the 2D and light-field(Galilean and Keplerian)mode can be electrically switched,and also the rendered digital patterns under the multi-perspective refocusing are exhibited.The extended depth of field(DOF)behaviors in different operation mode are demonstrated.The proposed techniques lay a foundation for developing graphene-based LC devices with a wide spectral range.Finally,the infrared spectrum broadening of the graphene-based LCMLA is carried out.A type of infrared liquid-crystal microlens array(IR-LCMLA)is developed using an isothiocyanato nematic LC material with high birefringence and the polycrystal-graphene LC anchoring properties.The infrared microbeam diffraction crosstalk introduced by the grooves formed by rubbing precoated polyimide film is eliminated,and then the infrared transmittance of the IR-LCMLA is enhanced remarkably,and also the electrically tunable focus characteristics in a wide spectral range of 0.9 to 11?m are analyzed.The proposed techniques construct a concrete basis for developing adaptive wavefront measurement and light-field imaging technologies.