The Study Of Micro-displacement Measurement Technology Based On Speckle Phase Vortex Correlation Method

Micro-displacement measurements are an important area of optical measurement. Traditional digital speckle correlation method has important applications in the field, but as the technology advances, the measurement method also requires continuous improvement. Speckle phase vortex is a common phenomenon in speckle, and the speckle phenomenon of phase vortices can be used to optical measurement. In this paper, the speckle phase vortex theory and measurement principle of digital speckle correlation method are combined to improve the traditional measurement methods. The specific contents are as follows:Firstly, we study the formation principle, size and light intensity of speckle, and analysis definition and symbols law of the speckle phase vortices. Also, we introduce the process of producing speckle phase vortex using Riesz transform and Laguerre-Gaussian transform. The center structure of phase vortex is researched, and the measuring principle of two digital speckle correlation methods is analyzed.Secondly, in order to improve measurement accuracy and resist noise interference of the conventional digital speckle correlation method in frequency domain, The correlation method of digital high order vortex speckle in frequency domain is proposed. Principle analysis of generating vortex beam by computer holography, the vortex speckle pattern in the diffraction area is obtained by means of the experimental platform. We study the nature of the high order vortex speckle pattern, and it is found that the high order vortex speckle pattern has anti-noise ability. Besides, an important characteristics is that the higher the order, the smaller the area of related intensity. When the high order vortex speckle pattern is introduced into digital speckle correlation method in frequency domain, we can get a related highlight in the correlator output surface, which is small size and energy convergence. The subtraction is applied to the measuring principle, so you can either eliminate background noise in image, and can get two related highlights before and after displacement. Then, correlator is improved to raising the sharpness of the output peak.Finally, when the traditional speckle phase vortex method is used to measure displacement of an object, the phase vortex point will change with the displacement of an object. A part of the phase vortex is produced, and the other part of the phase vortex is vanished, which leads to the error matching in the measurement process. The directional wavelet constructed speckle phase vortex correlation method is adopted. According to the ability of polarization analysis of directional wavelet, a network phase vortex point map with stable structure can be constructed. The two step measurement algorithm is proposed based on the network structure. Preliminary measurement is to determine the approximate the range of the search, and the exact measurement is to match the vortex points in the range of the search. This algorithm can greatly improve the correct matching rate of phase vortices.Through design MATLAB simulation program and set up the experimental platform, Theoretical and experimental data are statistically studied. It is proved that high order vortex digital speckle correlation method in frequency domain has strong anti-noise interference ability, and directional wavelet constructed speckle phase vortex correlation method improves the correct matching rate of the phase vortices. The two methods can improve the accuracy of the measurement.