Phase Unwrapping Algorithm In Digital Holographic Microscopy

Digital holography is a new holographic method of visualization measurement and characterization of three-dimensional micro-structure, with advantages of non-contact, quasi-real-time, high sensitivity, high precision, high resolution and whole-field. Phase unwrapping is an important part of three-dimensional reconstruction in digital holography, which directly impacts on the accuracy of the measurement in digital holography. However, it’s very difficult to get high precision phase unwrapping results due to noise, shadow and under-sampling factors in practical applications. Though many algorithms in recent thirty years have been proposed, but there is none of an algorithm to solve all of the problems in phase unwrapping. Therefore, it’s necessary to conduct further research on the phase unwrapping algorithm, and find out the optimal phase unwrapping algorithms which are suitable for applied to digital holographic microcopy in different situations.Through theory analysis, computer simulation and experiment demonstration, this paper addresses the application of the phase unwrapping algorithm in digital holographic microscopy. The main contents and the significant results are as follows:1. The current mainstream phase unwrapping algorithms are summarized in this paper. According to this, the phase unwrapping algorithms are divided into five categories in detail through scientific and practical method. Secondly, the basic theory of each kind algorithms and their advantages, disadvantages and application scope are described in detail. At last, the classical algorithms for each category are analyzed and compared.2. The basic theory and the solving steps of the minimum norm algorithm and the algorithm based on Fast Fourier transform are mainly elaborated, and compared the advantages and disadvantages of several representative algorithms of this two algorithms in detail. At last, computer simulations and experiments are carried out to verify the algorithms.3. The issues of comprehensive algorithm are studied in depth in this paper and the major categories, advantages and disadvantages of this kind of algorithm are expounded. An improved phase unwrapping algorithm based on image segmentation and merged is presented, for the phase unwrapping problem of the image with different interference characteristics. At last, the effective of the improved algorithm is tested and verified through computer simulation and experiment.4. Twelve kinds of classic phase unwrapping algorithms are realized by Matlab7.0, and they are used in the onions and Lygodium cells phase reconstruction of digital holographic. The performance of this twelve kinds of phase unwrapping algorithms are compared, and then found out the optimal phase unwrapping algorithm which are suitable for digital holographic microscopy in different circumstances.5. Digital holographic microscopy is applied for morphology characterization of Chinese medical decoction pieces cell in this paper, and obtained the size and morphological characters of the cells. It provides a new way for the microscopic identification of Chinese medical decoction pieces.