Preparation And Performance Test Of Coil-based Liquid Lens Driven By Dielectrowetting

Traditional cameras still stick to mechanically adjust the distance between lenses for regulating the focal length.Hence,the camera module is complicated and bulky,which not only not conducive to the design of lens miniaturization,but also reducing the life of the lens.The liquid lens adjusts its focal length by modulating the curvature of the interface between two different fluids using electrowetting on dielectric(EWOD),which is one of the most mature methods because it offers large optical tunability,high optical transmittance,fast driving speed,etc.However,the preparation methods of most current EWOD liquid lenses still suffer from complicated fabrication procedure and limited lens geometry.This paper proposes a new approach for the fabrication of variable-focus EWOD liquid lens.This technique is based on a particular structure named EWOD wire,which is a flexible conductive core coated with a soft insulating dielectric layer(like modified enameled wire),then wound or stacked into a coil as the lens cavity.After shorting the two ends of EWOD wire,the function of driving electrodes can be easily achieved.Therefore,the liquid lens cavity,sidewall electrodes and insulating dielectric layer can be fabricated in only one step.Hence,the lenses may be designed to have flexible shapes.In this paper,a cylindrical double-liquid lens is implemented and tested.The main contents of this paper are as follows:Similar to the production process of enameled wire,this paper designs and manufactures a onedimensional structure(named as EWOD wire)composed of "conductive wire core + insulating dielectric layer".After tightly winding the EWOD wire on a flat substrate to form a wire wall,the two-dimensional plane structure of " electrode on plate + insulating dielectric layer" is formed.The relationship between the contact angle of droplet and the voltage is measured in this structure and the results conforms to the Lippman-Young equation,verifing the feasibility of manufacturing coil based liquid lense.The three-dimensional structure of lens cavities made by EWOD wires with different shapes are fabricated.For comparing with traditional lens structure,the lens with the main body of a cylindrical coil is studied and fabricated in this paper.The measurement of focal length is carried out use the method of magnification,and results show that the relationship between the focal length and applied voltage follows the theoretical values.When the clear aperture of lens is 8 mm and the diameter of EWOD wire is 0.15 mm,the range of tunable focal length is(-∞,-35 mm]∪[ 78 mm,+∞)at a voltage of 0 to 235 V.What is more,the average response time of the liquid lens tested is approximately 37 ms,showing comparable performance to Corning? Varioptic? lenses.Lens imaging capability under modulated voltage is also measured,showing the high clarity and repeatability.Comparing the image at 0 V,the maximum magnification is 1.8 × at 235 V.Besides,the ability of the lens to focus on two objects is successfully demonstrated.Finally,the experimental result of the imaging resolution of this liquid lens is greater than 25.40lp/mm.