Research On Image Reconstruction Technology Of Imaging Through Random Medium And Explores Of Imaging With A Single Fiber

The transmission and scattering of light wave in random medium is one of the most active and fast growing branches of the electromagnetic theory, and it has become the common hot topic of different subjects which covers communications, biomedical imaging, remote sensing and environmental monitoring. In the field of imaging, the scattering of light in medium has been considered as a critical cause that degrades the imaging quality, therefore, how to eliminate the influences of medium on imaging has become the focus of research. As the recent studies show, however, the target image can be extracted from the scattered light which contains the information of object, on condition that the optical transmission property of the random medium is determined in advance; furthermore, compared with traditional imaging system, the obtained resolution is significantly improved. Thus, in special applications, the random medium has great potential to serve as an optical imaging component with high-quality. This thesis aims at imaging through random medium. The transmission property of random medium, the methods of measuring transmission matrix, and the methods of phase extraction which are indispensable to image reconstruction, are mainly studied. In addition, we regard a single multimode fiber as random medium and explore its endoscopic system.This thesis outlines the features of random medium in a systematic way, and its applications in super-diffraction limiting focusing and imaging are introduced. The reasons for the improvement in resolution of optical imaging system are analyzed. Then, the transmitting mechanism and characteristics of light wave in random medium are studied. Green function is adopted to describe the relations between the incident light wave and emerging light wave. Based on the discretization of the optical transmission channels on the input and output of random medium, the models of optical transmission matrix are established. Secondly, the principles and methods of measuring transmission matrix in spatial domain and spatial frequency domain are studied, and their corresponding imaging systems are introduced in detail. The experimental configuration and its controlling system of our own are also presented elaborately. Thirdly, three kinds of phase extraction algorithms, which are based on the extrema distribution of fringes, two-dimensional Fourier transform, and Hilbert transforms, respectively, are studied. Considering the particularity of the system of measuring transmission matrix in space frequency domain, a new phase demodulation algorithm based on modified Hilbert transform is proposed to extract the phase from the speckle interference pattern. The feasibility and validity of this algorithm is verified through experiment, and the complex amplitude is obtained by intensity pattern, thus the measurement of transmission matrix in space frequency domain is completed. Considering that the transmission matrix is obtained, the angular spectrum of target can be extracted from the scattered field by using projection operation, and further the target to be detected can be reconstructed. Finally, as the technique of imaging through random medium can be extended to the case of imaging with a single multimode fiber, the advantages and the application prospect of a single-fiber endoscopy are introduced systematically, meanwhile, a system structure and an implementation scheme of a single-fiber endoscopy are proposed.