The Research Of Cosine Phase Unwrapping Method In Optics Phase Measurement

Phase measurement technology is a high precise method in interference measurement and phase profile measurement. Fringe skeletons method, heterodyning, Fourier transform method and phase-shifting method are major methods. The phase-shifting method has predominance in phase measurement such as high precision, high speed of calculation, the ability to suppress noise in fringes and asymmetry of image sensor, but produce a phase map which is wrapped in the range -π to π, is called wrapping phase due to the period of trigonometric function. In order to get the original phase of the measured physical quantity, the process of phase unwrapping is needed, and has become the key of interferometry. Most of phase unwrapping methods are based on tangent wrapping phase, and the tangent phase unwrapping methods have the disadvantages which can't be filtered and can't judge the phase shifting precision.By use of the phase-shifting technology, the background and amplitude of interference fringes can be obtained, and a novel phase unwrapping method based on cosine function is proposed. The time serial interfere fringes are recorded, and then the phase cosine functions can be obtained by removing the background and amplitude from the fringes. The arccosine functions of phase cosine functions, which are called phase cosine wrapping function in this paper, can be unwrapped by utilizing the additional normal orientation information. The experimental analyses show that high precise cosine unwrapping phase can be get either by path dependence phase unwrapping method or by path independent least squaresphase unwrapping method.The characters of cosine wrapping phase are analysis in the paper.The wrapping range of cosine wrapping phase is [π, 0, π], the phase jumping points disappear, and the gradient orientation information of original phase lost because cosine function is even function. Compared with tangent wrapping phase, the phase cosine wrapping function is consecutive and can be filtered, and the unwrapping process is easier than tangent wrapping phase. The influence of phase-shifting errors on phase cosine function is not only positions but values of the wave crest and wave trough. The more precise the phase-shifting is, the closer the values of cosine function to +1 at wave crest and wave trough are. The Experiment results show that cosine unwrapping method has the equivalent precision with tangent unwrapping method. The problems of cosine phase unwrapping method are: 1. the residual noise in the phase cosine function after phase-shifting filter can be eliminated greatly, but the position of main wave crests, main wave troughs and zero points need judged correctly; 2. The cosine phase unwrapping method can not apply to the phase measurement of close interference fringes and the boundary request ion, which is the greatest disadvantage of this phase measurement method. The primary application of cosine phase unwrapping method in the measurement of dynamic process is discussed at the last part of the thesis.