Technical Research Of Longitudinal Correlation Of Speckle Fields Based On Coded Modulation

The decorrelation phenomena of speckle fields in three-dimensional space,whichmay affect the interference fringe visibility and reduce the accuracy of surfacedisplacement measurement,is the main factor that restrict the development of speckleinterferometry technique.The cause of the decorrelation is that the speckle grain inmicro have3D structure and thus have transversal and longitudinal size.When thedisplacement or deformation of the object is longer than the speckle size,decorrelationoccurs,and then accurate imformation wanted cannot get.We propose a coded specklesystem that the phase of the speckle field is modulated by a cubic phase mask.Thelongitudinal correlation of speckle fields is improved effectively by thismethod.Simulation and experiment are carried out to prove this conclusion. Thisthesis includes the following works:1、 Design the general model of coded speckle system.Choose the4f system andcubic phase mask to do the research by carefully study of the optical systems andcoding methods.2、 Complete the simulation with MATLAB.The longitudinal correlationcoeffections of both coded speckle fields and that without a phase mask are drawnby the computer.The simulation of single lens system and4f systems both havegood results.3、 The experiment verified the validity of the cubic phase mask in a coded specklefields.The experiment results also conform the simulation value.4、 Experiment with coded speckle fields based on the Michelson interferometer isdone. Interference patterns of deformation in the same time are comparedbetween the coded spekle fields and the origin speckle fields.The result of theexperiment show the advantages of coded speckle field in speckle interferometry.