Research On Beam Pointing Control Technology Electrowetting-based Liquid Prism Array

Beam pointing control technology has important applications in solar lighting,free-space optical communication,directional infrared countermeasure,laser radar,projection display,optical switch and other fields.The traditional beam pointing control technology relies on the mechanical device to change the direction of the optical axis to achieve the beam pointing control.Therefore,there are problems such as complex operation,slow response and low operation accuracy.The liquid prism based on electrowetting-on-dielectric(EWOD)have many advantages,such as simple structure,easy integrate,non-polarization dependence on multi-wavelengths,fast response speed,no need to overcome the inertia effect during motion,and easy to realize array.In this paper,a liquid prism array based on EWOD is designed and applied to spatial beam pointing control.The main research work is as follows:Firstly,introducing the research background and research progress of beam pointing control technology,explaining EWOD working principle,derivation the Young's equation and Young-Lippmann equation.At the same time,analyzing the applications of electrowetting effect in the field of display,optical imaging and beam pointing control.Secondly,designing the structure of liquid prism unit based on EWOD,analyzing the working principle and deriving the formula for calculating the beam steering angle.By selecting a specific combination of liquids,the saturation contact angle and working voltage can reduce and consequently the range of beam steering range is improved.An one-dimensional liquid prism array and a twodimensional liquid prism array based on EWOD are designed.According to geometrical optics and EWOD theory,the relationships between the beam steering control range,the maximum beam steering angle,the interval between adjacent prisms,and the liquid refractive index are analyzed and discussed.Theoretical analysis shows that the one-dimensional liquid prism array can control the beam pointing and the tune of focus in two-dimensional space,while the two-dimensional liquid prism array can control the beam pointing and the tune of focus in three-dimensional space.Thirdly,the theoretical model of the EWOD liquid prism unit,one-dimensional array and twodimensional array are constructed in COMSOL.Then the evolution of the interface in the liquid prism unit and the beam steering performance of the liquid prism array system is simulated under different voltage conditions.By adding ray tracing module,the beam pointing after passing through the system is reproduced.The results show that the liquid prism array can realize the beam steering control in a certain range.The factors that affect the performance of the device are analyzed and discussed,such as the beam steering angle and the distance between prism units.By selecting a specific combination of liquids,the saturation contact angle can decrease to 45 degrees,and consequently the range of beam steering angle for liquid prism unit reaches 38 degrees(-19 degrees to 19 degrees).As r is set to 6mm,the one-dimensional liquid prism array system can realize the steering region is in inverted isosceles triangle whose apex angle is 38 degrees,the vertex is located at Z=15.81 mm in the z-axis.The two-dimensional liquid prism array system can realize the steering region is in a conical region whose apex angle is 38 degrees,and the corresponding vertex of the cone is located at Z=15.81 mm in the z-axis.