Research On Novel Liquid Crystal Lenses

Liquid crystal lenses,serving as electronically tunable devices,have found significant applications in imaging and display technologies.Since the initial proposal of liquid crystal lenses by Sato in 1979,various lens structures have been introduced,including cavity structures,hole-patterned structures,modal control structures,and patterned electrode structures.Despite their potential,traditional liquid crystal lenses face challenges such as high aberration,low optical power,and small aperture size,et.al.This thesis proposes novel design approaches for liquid crystal lenses to address the limitations of conventional designs,aiming to enhance lens performance and facilitate practical implementation.The parabolic phase distribution is desired for liquid crystal lenses;however,achieving this goal remains challenging.Considering the linear response region of liquid crystal materials,within which the phase of the liquid crystal layer has a linear response to the voltage,the parabolic voltage distribution is a prerequisite for achieving parabolic phase distribution.Two electrode design methods are proposed in this thesis to generate any desired voltage distribution,including parabolic voltage distribution.The first method involves a rigorous equation-solving approach,where a differential equation is established based on the desired voltage distribution.Subsequently,the equation is solved to derive analytical solutions for the electrode structure.The second method involves designing a length variation function for discrete electrodes,and then connecting these discrete electrodes to produce the desired voltage distribution.The designed electrode structures,referred to as “generation units” are used to produce specific voltage distributions.To ensure voltage coverage across the entire aperture of the lens,concentric circles,or parallel line electrode structures,termed “diffusion units” can be introduced.This modular design enhances the flexibility of liquid crystal lens design.Based on the proposed design methods,the following specific research findings and conclusions are presented:1.Two methods are employed to design circular liquid crystal lenses with parabolic phase distribution.For the equation-solving method,assuming a spiral electrode structure for the generation unit,a differential equation is established and solved to obtain the analytical expressions for the electrode structure generating parabolic voltage distribution.The combination of diffusion unit composed of concentric electrodes achieves a parabolic voltage distribution across the entire aperture.Subsequently,restricting the voltage within the linear response region of the liquid crystal material ensures the realization of a parabolic phase distribution throughout the aperture.This method only requires the uniform distribution of concentric arc electrodes with equal density from the inside to the outside to obtain a parabolic voltage distribution.Therefore,this design method is simpler.Both methods demonstrate circular liquid crystal lenses with parabolic phase distribution and tunable focal lengths through two driving voltages,offering a straightforward driving mechanism.Additionally,the lens’ s optical power is directly proportional to the difference between the two driving voltages,and the lens maintains a parabolic phase distribution throughout the focusing process.In the experiments,the corresponding electrode structures were fabricated using photolithography techniques,leading to the preparation of liquid crystal lenses.The results confirmed the excellent optical performance of the liquid crystal lenses designed through both methods.2.By extending the design principles,comb-type electrode structures that can generate a parabolic voltage distribution are proposed.These electrode structures have been applied to liquid crystal lenses,and the results demonstrate excellent lens performance.Further investigation reveals that placing two orthogonal comb-type electrodes on the upper and lower substrates can achieve the required voltage distribution for rectangular aperture liquid crystal lenses.This design helps to avoid light scattering issues caused by electrode leads and offers advantages such as positive-negative tunable focal lengths and no need for a High-resistivity Layer(HRL).Furthermore,based on a single rectangular aperture lens,a corresponding lens array is proposed.This lens array can be driven to function as different devices,such as a horizontally or vertically oriented cylindrical lens array,as well as a rectangular aperture lens array.Experimental results show that the proposed rectangular liquid crystal lenses and lens arrays exhibit parabolic phase distribution with minimal aberrations.Based on the comb-type electrode structure and the phase response curve of the liquid crystal material,a liquid crystal lens that can enhance the utilization efficiency of the birefringence Δn is achieved by designing a unit envelope function.The results show that the utilization efficiency of positive lenses and negative lenses has been increased by68.8 % and 64.4 % respectively.3.In order to achieve liquid crystal lenses with large aperture and high optical power,the thesis proposes the design methods for circular and rectangular Fresnel liquid crystal lenses.The Fresnel liquid crystal lens contains many Fresnel zones,and ideally the phase distribution within these zones should be parabolic.After unwrapping the phase,all the phases within the zones should form a perfect parabolic distribution.The thesis applies discrete arc electrodes and comb-type electrodes to the design of the Fresnel lens,successfully achieving circular and rectangular Fresnel liquid crystal lenses with parabolic phase distributions.Experimental results show that the phase of these Fresnel liquid crystal lenses can be almost perfectly restored to a parabolic distribution after unwrapping,and the measured aberrations are small.This type of lens is expected to be used in adjustable-focus eyeglasses,AR/VR,AR-HUD and other devices.4.This thesis introduces the design of circular lenses,cylindrical lenses,rectangular aperture lenses,and Fresnel lenses with a shiftable optical axis,achieved by incorporating a comb-type electrode structure with a linear voltage distribution.For circular lenses,circular Fresnel lenses,and cylindrical lenses,the optical axis can shift in a single direction,while rectangular aperture lenses and their Fresnel counterparts allow shift in two dimensions.These lenses theoretically offer high-precision optical axis shift while maintaining a parabolic phase distribution.The thesis details the design methods and operational principles of lenses with a shiftable optical axis,and experimental results confirm high-precision optical axis shift and excellent optical performance.This thesis not only delves deeply into the phase distribution and structural design of liquid crystal lenses but also proposes a systematic method for designing highperformance liquid crystal lenses,opening up new avenues for research and application in this field.This innovative design approach not only enriches the design theory of liquid crystal lenses but also provides robust technical support for their practical and diversified applications.The research results of this thesis have been preliminarily applied to variable-focus glasses products,achieving significant practical-level outcomes.This application not only validates the effectiveness and practicality of the research findings but also demonstrates the broad application prospects of liquid crystal lens technology in the optical field.