Study On Electrically Tunable Plenopitc Imaging Method Based On Liquid-crystal Microlens Array

Plenoptic imaging is a new type of three-dimensional(3D)imaging developed rapidly in recent years.The plenoptic camera is a single-lens light-field imaging device using a fixed-focus microlens array coupled with a photosensitive array,which demonstrates several inherent features such as the fixed optical configuration and the difficulty in adjusting the depth of field(DOF).As the directional resolving based on 3D plenoptic imaging data occupies a relatively large imaging sensor space,the resolution of the rendered images formed is lower than that of the two-dimensional planar image captured with the same imaging sensor.An electrically tunable liquid-crystal microlens array(ETLCMA),which is constructed based on the optical anisotropy and birefringence of the LC and fabricated via standard microelectronic processes,is a type of gradient index micro-optics architecture utilized to converge or diverge incident beams.Compared with conventional silica microlenses with curved surface,the ETLCMA with planar end faces demonstrates some remarkable characteristics including electrically tunable focal length,dynamically adjusting light transmission energy and photorefractive efficiency.In order to expand the function of the plenoptic imaging method,a LC-based control-light micro-optics structure is introduced and deeply researched to realize electrically tunable plenoptic imaging.The main work of this dissertation is as follows:Firstly,an ETLCMA with an arrayed micro-circle-hole electrode is simulated adopting the relaxation method and the finite difference method based on the fundamental features of the nematic LC materials and the elastic continuum theory.The director distribution formed by the electric-field stimulated in the LC micro cavity,and the phase retardation of the extraordinary beams of the incident light,are analyzed under the condition of loaded signal voltage with different root-mean-square amplitude over LC layer of variable thickness.The characteristics of light converging and electrically tunable focal length of extraordinary beams along radial nonuniform electric field are given theoretically.Secondly,the electrically adjusting DOF plenoptic imaging based on the ETLCMA with aluminum and indium-tin-oxide electrodes is proposed.The corresponding mathematical model is established.The basic imaging principles and its electrically tunable DOF principles are given.A prototype of the electrically tunable plenoptic camera(ETPC)is constructed and utilized to carry out electrically tunable DOF experiments,which indicate that the DOF range can be adapted significantly only through changing the signal voltage applied over the ETLCMA.The rendered images corresponding to different depths and different viewing angles as well as all-in-focus images,can also be obtained after post processing.Compared with current plenoptic imaging methods,the developed ETPC can be used to extend the DOF significantly.Thirdly,a 3D spatial projection transformation model according to LC-based ETPC is established.The algorithms for depth estimation,3D spatial coordinate and motion parameter measurements are given.The depth resolution and other problems are discussed carefully.The 3D spatial parameters of both the static and moving targets are measured based on an ETPC calibrated,which means that the 3D coordinate,motion velocity and attitude change of the targets can be obtained effectively.Fourthly,an integrated imaging method including electrically tunable plenoptic mode and planar imaging mode based on an ETLCMA with ITO electrodes is proposed.Through switching on and off the ETLCMA,the plenoptic imaging mode and the planar imaging mode can be transformed freely.A dual-mode camera prototype is constructed and continuously used to acquire both the plenoptic image and planar images of the same scene.The 3D structural information of each component of the scene can be acquired through computation of the plenoptic image data.High resolution 3D reconstruction can be performed through selecting planar image constituent units through image matching.The dual-mode integrated imaging method combines the light field imaging and the planar imaging together which can make full use of the advantage of plenoptic 3D data acquisition of the plenoptic imaging and the high resolution of the planar imaging.Lastly,an ETLCMA based on graphene electrode for infrared imaging is proposed and also used to perform plenoptic imaging detection.The ETLCMA with arrayed micro-circle-hole electrode are fabricated through transferring graphene film from copper foil onto glass substrate or zinc selenide substrate by wet transferring operation.The light focusing efficiency and the electrically tunable focal length behaviors in visible range are analyzed.The near infrared imaging characteristics are obtained by collecting point-type of plenoptic patterns,which lay a foundation for further developing the infrared plenoptic imaging technology.