Study On The Application Of Optical Focusing And Beam Deflection Based On Liquid Crystal Devices

Liquid crystals（LC）have birefringence properties,so the LC device can realize the phase control of incident light,such as converging light,diverging light and beam deflection.When the LC device plays the beam deflection function,it is generally called a LC beam deflector.It can control the direction of the beam and is often used in optical tweezers,laser radar and so on;when it is used to converge or diverge the light,it is generally called LC lens which has special functions such as electronically controlled focal length,optical axis movement and so on.It is often used in autofocus,intelligent imaging.To achieve these functions,it is necessary to form the required gradient distribution of electric field in the LC device.At present,many methods to achieve the gradient-distributed electric field have been proposed by the researchers.Among them,the LC devices based on mode control are more applied,and this approach is a good solution to the above problem.In this thesis,a new type of LC device based on the mode control is studied,which can realize LC lens or LC phase wedge.This thesis focuses on the driving method of this LC device to realize the controlled beam deflection and variable focal length.The main contents are as follows:Firstly,the structure of the LC device based on the principle of mode control is introduced,which has bar-shaped electrodes plated on the upper and lower substrates and uses the high-resistance layer for voltage division.The expression of the effective voltage in the effective area is derived and the electric field is simulated when the LC device works in the lens state and the optical phase wedge state respectively,and the driving method for the LC lens to realize the shift of the lens center is also derived.The works focuses on the driving method of the LC phase wedge and derives its theoretical deflection angle under different directions.Then,the driving method of the LC lens is experimentally verified,the focusing experiment using the periscope lens is completed,and the negative LC lens with a square aperture is fabricated using negative LC.Similarly,the driving method of the LC phase wedge is experimentally verified,and the beam deflection experiment is completed,and the accuracy and quality of beam deflection are measured.Finally,due to the limited deflection capability of the single-aperture LC wedge,two methods are proposed to achieve large-angle beam deflection: the first is an arrayed Fresnel-type LC phase wedge,which can significantly increase the deflection capability of the device by achieving multiple identical wedge phase distributions in the effective area through a special electrode structure;the second is the LC beam deflector based on optical axis movements,which can achieve beam deflection without mechanical movement and eliminate stray light by the movement of the optical axis of the LC lens.The studied LC device has low driving voltage,any rectangular aperture,variable focal length and the function of beam deflection.It has broad application prospects in the fields of beam steering and intelligent imaging.