Study Of Phase-modulation Based Computational Correlated Imaging Technology

Computational correlated imaging(CCI)is a new imaging method,which uses the correlation between intensity fluctuations of optics fields,breaks some limitations in traditional imaging and attracts a lot of attentions in the field of optical imaging recently.Aiming at the key problems in CCI,this dissertation carries out the corresponding researches as follow:1)In the CCI system using traditional speckle,the axial location of the object should be the prior knowledge to reconstruct an in-focus image,otherwise a defocused image will be seen.To solve this problem,the CCI using pseudo non-diffractive(ND)speckle is proposed.In the given system,we demonstrate that as compared to the conventional speckle,the depth-of-field and the lateral spatial resolving power of the CCI using ND speckle are improved by?2-3 times and 30%respectively.The in-focus image of the object can be reconstructed without the need of its accurate axial location by using the proposed method.2)In the CCI system using traditional speckle,the degree of defocus of the reconstructed image reflects the difference between the estimated depth and the practical axial location of the object.In the traditional method,the images at all the axial locations are formed and the corresponding degree of defocus are evaluated to achieve the practical axial location,which requires a number of iterations,brings a heavy workload and reduces the efficiency of CCI.To solve this problem,a fast depth estimation method for CCI in deep-Fresnel(DF)region is proposed.In this method,we firstly build the defocus model of CCI with the object in DF region.The function of Deviation-Based Correlation is utilized to evaluate the degree of defocus of the reconstructed images.DBC reaches the global maximum in DF region,and keeps monotonic in a relative long region on each side of its maximum position.Based on the characteristic of DBC,the fast iterative algorithm for searching the axial location of object is designed.It is demonstrated that in the given system(the number of all the depth:N)the axial depth of an object and its in-focus image could be obtained in log2 N iterations(the number of reconstructed images less than 2 log2 N)by using the proposed method with the error of estimated depth smaller than the longitudinal coherence length of the speckle.Compared to the traditional method(scanning all the depth),the required iteration number of the proposed method is significantly reduced.3)The solid scattering layer located between the object and the bucket detector will not affect the correlation between the signal beam and the reference beam,but possibly reduce the energy of the light arriving the bucket detector,in which case the bucket detector might be in the low light condition and the influence of the device noise should be considered.Aiming at this problem,the behavior of CCI in low light condition is studied.We build a general model of Signal-to-Noise Ratio(SNR)for CCI by considering the device noise.To verify the proposed model,the Electron Multiplication Charge Coupled Device(EMCCD)is utilized as a bucket detector,the corresponding SNR formula of CCI is deduced based on noise characteristic of EMCCD and the key parameters of governing the quality of reconstructed images are given,which is confirmed experimentally.Finally the anti-scattering imaging is achieved by controlling the EMCCD's parameter in low light condition with the scattering layer placed between the object and the detector.4)The solid scattering material located between the source and the object might break the correlation between the signal beam and the reference beam,however this effect on CCI has not been studied deeply.For this issue,the 'anti-scattering' capacity of CCI is analyzed in this scattering condition by using the discrete point scattering function(DPSF).Firstly,we introduce and analyze the concept of DPSF based on the characteristics of the projected patterms(super-pixel size:d)and the point-scattering-function(width:w0).The behavior of CCI with solid scattering material located between the source and the object located is analyzed by using DPSF.We theoretically and experimentally demonstrate that the blurry effect on the reconstructed image is visible as d<<w0/2,however it can be highly restrained as d increases to be comparable to w0/2 or larger.