Research On Focal Depth Extension Method Of Multiplexed Lens Based On Liquid Crystal Spatial Light Modulator

As the optical element with long focal depth has broad application prospects in laser direct writing,rapid prototyping,laser engraving,drilling,cutting,welding and other engineering fields.At present,although there are many ways to achieve the long focal depth,where are still many technical bottlenecks in practical applications.A liquid crystal spatial light modulator is applied to the study of long focal length optical elements,which has flexible programmable characteristics and will give more flexibility and autonomy.In this paper,a method for the focal depth extension of a multiplexed lens based on liquid crystal spatial light modulation is studied.The main research work includes:In this paper,several phase measurement method of liquid crystal spatial light modulator are compared and the phase modulation characteristics of XGA2 liquid crystal spatial light modulator are measured by the Mach-Zehnder interference optical path.The relative movement amount and period of stripes are extracted from the interference fringe image by image processing combined with the maximum probability principle,and using the least square polynomial fitting method to get the curves of phase modulation of liquid crystal spatial light modulator.The principle of loading Fresnel lens with liquid crystal spatial light modulator is studied,and the sampling problem and diffraction efficiency of Fresnel lens are discussed in detail.On this basis,Using Matlab programming,a number of different focal length Fresnel lenses and liquid crystal blazed grating is embedded together,and then written into the liquid crystal spatial light modulator by a random sampling method.The focal depth is extended according to the principle of the mutual overlap of the axial focus of each lens,and a grayscale image of the multiplexed lens with a depth of focus of 1000~1040 is fabricated.The focusing experiment of multiplex lens is simulated by Matlab,and the principle of simulation experiment is introduced,and the simulation results are analyzed.On this basis,the multiplexed lens focusing optical path is built.The multiplexed lens gray scale and the single lens gray scale are respectively loaded into the liquid crystal spatial light modulator.The focal spot at different positions was obtained by CCD,and the experimental results were compared and analyzed from two aspects of the intensity and intensity of the focal spot.The experimental results show that compared with single lens,focal depth multiplexing lens has been prolonged,and in the depth of focus range,its resolution remained unchanged and close with the single lens,confirmed the feasibility of extending the depth of focus method.