Research On Liquid Crystal Lens Based On Photoalignment Technology

Benefiting from the breakthrough of photoalignment materials,the liquid crystal photoalignment technology has been improved by leaps and bounds.Soon after,with the support of integrated chip and optical engineering technology,the digital exposure system was born.Since then,the production of multi-functional liquid crystal light modulator has a solid technical foundation,and the design of liquid crystal devices with various functions has become a hot direction.A variety of ultra-thin liquid crystal optical devices based on subwavelength structure have been designed and manufactured by using the abrupt phase principle.These devices can generate phase discontinuous wavefronts and be used for optical field manipulation.Compared with the traditional gradual phase-accumulation lens,the liquid crystal ultra-thin lens realizes the wave-front manipulation by optimizing the subwavelength structure,which is not only more diverse in function,but also a solution to solve the problem in a smaller volume.At the same time,according to different use scenes,can selectively make electronic control liquid crystal lens box or liquid crystal film lens.Bifocal lenses can focus the incident light in a transverse or longitudinal position and are more efficient than single-focal lenses in many applications.For example,in some communication systems,optical signals need to be separated as needed,and polarized light images need to appear in different locations.In addition,bifocal lenses also have potential applications in nanoscale particle manipulation and optical tweezers.The achromatic lens can eliminate the effect of chromatic aberration in one wave band,and is an extremely important device in color optical imaging and display systems,which directly affects the performance of these systems.The main content of this thsis is as follows:(1)Here,millimeter-scale transverse and longitudinal liquid crystal bifocal lenses(LCBLs)are proposed and designed based on the geometric phase and holographic principle,and the relative intensity of foci can be easily controlled through a simple polarization selection.LCBLs are further fabricated with the standard LC photoalignment technology and the diameter can be up to 1 mm,which can be easily integrated into existed optical setups.The focusing performances of LCBLs to control the relative intensity of foci are also experimentally demonstrated,and the results match well with our designs.The proposed millimeter-scale LCBLs working in the visible wavelength are proved to be practical.(2)Based on the Pancharatnam-Berry phase theory,achromatic lenses at visible wavelengths are designed and fabricated.Based on the image phases of three focusing lenses with the same focal length at different wavelengths,the phase distributions of achromatic lenses are obtained by superimposing them.In the experiment,it is found that three focal points can be observed in different positions when the monochromatic light is incident,and the light of three wavelengths can be focused in the designed focal plane.The achromatic lens achieves achromatic function at the corresponding focal plane through partial reduction of focusing efficiency.