Research On Focusing System Of Electrowetting Lens And Liquid Crystal Lens

In the traditional focusing optical system,the driving device was used to move part of the lens or the whole system to realize focusing,which leads to the large volume and complex structure of the system.As a new optical element,the electrowetting liquid lens can adjust the focal length by changing the shape of liquid interface driven by voltage,which can be used in the design of focusing system with strict volume restriction.However,the electrowetting liquid lens was usually necessary to combine the fixed focal length lens to form a complete focusing system due to its small aperture and limited focal length range.Meanwhile,the aberration characteristics of the focusing system based on the electrowetting liquid lens will change with the curvature radius of the electrowetting liquid lens during the focusing process.The aberration of the fixed focus length lenses cannot be changed,which leads to the image quality deviation of the system under different object distances.As a kind of gradient refractive index lens based on the electro-optic effect of liquid crystal,the liquid crystal lens can flexibly adjust the refractive index distribution by changing the driving voltage,which has good effect on aberration correction.In this paper,the liquid crystal lens was added to the electrowetting liquid lens focusing system to correct the aberrations of the system during the focusing process,so as to form a common focusing system of electrowetting lens and liquid crystal lens with high image quality,small size,simple structure,no mechanical movement and so on.The specific research contents are as follows:1.The focusing system of 33-565 electrowetting liquid lens and the liquid crystal lens were modeled in Zemax.During the modeling of the liquid crystal lens,the gradient 2-facet was adopted to simulate the gradient refractive index distribution of the liquid crystal lens with highorder terms under monochromatic light wavelength.Furthermore,to represent the dispersion of liquid crystal lens in wide spectrum,a method of using gradient 6-facet to represent the dispersion of liquid crystal lens was proposed by combining the liquid crystal continuous elastomer theory and the Cauchy dispersion model of liquid crystal.2.Under the common 850 nm LED light source in the field of machine vision,the aberration characteristics of the electrowetting liquid lens focusing system at six typical object distances from 200 mm to infinity were analyzed.The liquid crystal lens was added to the system to correct the monochromatic aberration of the system.Through the analysis of the correction results,it was found that the geometric radius of the maximum diffuse spot of the system was from 44.696 μm to 7.423 μm.The monochromatic aberration of the system was well corrected.In order to reduce the response time of the liquid crystal lens,the liquid crystal lens was designed as five 1/5 original cell thickness multi sheet liquid crystal lenses stack structure.It was found that the designed structure has the same good correction effect on the monochromatic aberration of the system.In addition,the gradient refractive index distribution of the liquid crystal lens in the above two systems was derived,and its feasibility was analyzed.3.The chromatic aberration characteristics of electrowetting liquid lens focusing system and electrowetting liquid lens co focusing system with liquid crystal lens were compared and analyzed under six typical object distances from 200 mm to infinity in visible light band.It was found that the addition of liquid crystal lens increased the chromatic aberration of the system.Under all object distances,the geometric radius of the maximum diffuse spot of the system has reached 143.049 μm,and the obvious separation of the color spots appears in the edge field of view,and the axial chromatic aberration increased to 0.5 mm.A color difference correction system was designed,which adopted a double-layer liquid crystal lens structure.Two kinds of liquid crystal materials with different dispersion characteristics were combined to form a positive and negative lens group to correct the color difference introduced by the liquid crystal lens.Through optimization,the optimal system structure for correcting chromatic aberration was obtained,and the chromatic aberration of the system was analyzed.Under all object distances,the geometric radius of the maximum diffuse spot of the system was reduced to52.923 μm.The axial chromatic aberration was better than 0.2 mm,and the axial chromatic aberration and vertical chromatic aberration of the system are well corrected.