Designing,Fabrications And Applications Of The Three-dimensional Structural Liquid Crystal Elements

Compared with the traditional optical devices based on dynamic phase,the plane optical devices have a quantity of merits,such as being thinner,being more multifunctional and having a higher freedom of design.Therefore,the design and application of the plane optical devices based on the geometric phase recently have attracted considerable attention.The plane optical devices based on liquid crystals,a member of soft matter,have been applied in the fields like light manipulation,display technology and biomedical instruments due to their smaller volume,thinner thickness,higher efficiency and sensitivity to polarization.The ordinary liquid crystal geometric phase devices can manipulate the amplitude,polarization state and phase of light by the special design on the two-dimensional planar structure.However,as the demand for optical devices in practical application scenarios becomes higher and higher,the application of the liquid crystal devices with two-dimensional structure is severely limited.For an instance,only the fabricated devices working at the situation that the incident light wavelength meets the half-wave condition have a high efficiency,which causes that the working window of the devices is so narrow that the devices are unable to meet the current need.With liquid crystal materials developing constantly and the researches going deeper,the study on the free degrees of liquid crystals in threedimensional structure shows its immense value.By their distinctive advantages,a wide working window,a high tolerance rate of incident light and a high conversion efficiency,the liquid crystal geometric phase devices with a specially designed threedimensional structure have played a vital part in the field of light manipulation.Different from the traditional liquid crystal geometric phase devices,the liquid crystal geometric phase devices with a three-dimensional structure have a higher free degree.Several three-dimensional geometric phase optical devices with special functions have been proposed in this thesis based on the research of the liquid crystal helical structure in three-dimensional space.Verifying the feasibility of the fabricated devices in the experiments and application scenarios,the main research results that have been achieved are as follows:1.The simulation design of the liquid crystal geometric phase devices with a three-dimensional structure is accomplished and verified in experiments via the extended Jones matrix and scalar diffraction theory.Taking advantage of dual-beam interference exposure,optical imprinting,digital micromirror device,the complex orientation of liquid crystals in two-dimensional plane has been accomplished.Then mixing the liquid crystal materials with the corresponding chiral agent is to acquire the designed three-dimensional structure of liquid crystal geometric phase devices.As the above-mentioned simulation and experimental schemes has shown,it’s feasible to develop the liquid crystal devices performing special functions with a threedimensional structure,which makes it possible to achieve the system integrated with more optical functions without losing the high efficiency.It means that as the three-dimensional structure has been studied further,there are more innovative liquid crystal optical devices.2.Optical imprinting with dual-twist liquid crystal polarization gratings as templates,an innovative scheme,has been proposed,where the dual-twist structured liquid crystal polarization gratings are used as templates to fabricate waveguide gratings with sub-wavelength periods and the gratings maintain good optical waveguide performance.This scheme solves the issue that the ordinary imprinting schemes currently cannot accomplish the imprinting of sub-wavelength period gratings,which directly results in sub-wavelength polarization volume gratings applied in near-eye display being unable for mass production,and also offers a feasible scheme for the mass production of sub-wavelength gratings.3.A new polarization conversion system based on the combination of liquid crystal polarization gratings with three-dimensional structure,quarter-wave plates and the designed lens array has been proposed,breaking through the limitations about the energy loss and low efficiency of traditional polarization conversion system.Besides,the polarization system has also been verified in the experiments to make sure the system can be used in the field of display.The system extremely increases the utilization ratio of light energy and polarization conversion efficiency,and will offer an innovative scheme for the field of polarization conversion,liquid crystal display,polarization manipulation and so on.4.Utilizing the cholesteric liquid crystals property of total reflection for the light with a certain wavelength,a new reflective edge enhancement scheme has been proposed and achieved,which hugely simplifies and shortens the light-path design compared with the traditional all-optical image processing system,and breaks the limitations that traditional optical image processing system works when the wavelength of incident light is in a certain range.Besides,building the confocal microscopy system,the feasibility of this scheme for being applied in the field of biological micrograph has been proved,which provides an innovative reflective scheme for the development of all-optical image processing.