In this paper, we propose a robust phase unwrapping algorithm that can be applied to optic interferometry based on combing the theory of residues and local phase information to mask out the discontinuous regions in the unwrapping. Unlike previous methods, which require subjective appraisal to determine the threshold value of the second differences in a locally unwrapped phase empirically, this technique sets the threshold value in a straightforward way. The technique aims to minimize the loss of phase information produced by erroneous distinguished pixels, and simplifies the unwrapping process. Experimental results on complex discontinuous objects are presented to illustrate the validity of this technique.
The SS-OCT system was constructed using a swept laser source and a compact Michelson interferometer. The outputs of sweep source include laser signal and k-trigger signal. The laser signal realizes spectral interference and the k-trigger signal realizes acquisition interferometer signal with uniformly wavenumber interval. However, there are two problems. The first one is that the output wavenumber of the source changes non-linear with time. To solve this problem, a wavenumber phase equalization algorithm is proposed. The second problem is that the unfixed delay between the spectral calibration signal k-trigger and the OCT signal, which makes the result of spectral calibration incorrectly. Aiming at the asynchronization between the acquire OCT signal and the k-trigger signal, an algorithm of k-clock delay correction based on cross correlation is adopted to correct the delay. The SS-OCT system could be used for accurate measurement the curvature of the laser focusing lens due to its excellent advantages such as non-destructive, high resolution and high inspection speed. The 2D tomography maps of a laser focusing lens are measured by this system and real-time images are obtained.
A high speed swept source optical coherence tomography (SS-OCT) system has been proposed for tomographic map of spatial light modulator. In the optical arrangement, a swept-source with 100 kHz axial-scanning rate and a compact Michelson interferometer was applied. The implemented SS-OCT system has an axial resolution of 15μm and penetration depth of 12mm. The two-dimensional tomographic grayscale maps of the sample can be obtained in real time. As a result, the thickness of glass substrate, liquid crystal layer and the silicon substrate could be obtained simultaneously. Compared with the traditional detection methods, The SS-OCT system has the characteristics of fast imaging speed, stable repeatability of measurement with high-resolution and non-destructive.
The handheld target greatly expands the fields of the vision measurement systems. However, it introduces extraction errors and position errors, which degrades the positioning precision of the vision measurement systems. In order to evaluate the influence of the handheld targets on the accuracy of T-VMS, we first analyzed the positioning principle of the visual measurement system and established the precision model under two typical structures of the T-VMS. We then studied the extraction errors and position errors introduced by the handheld targets and quantified the errors. Finally, we discussed the influence of the said errors on the positioning in 3D space with system precision model. We applied the precision model in an actual T-VMS to confirm its feasibility and effectiveness, and found that it indeed estimate the errors introduced by the handheld targets effectively.
Phase unwrapping is a significant procedure that has raised a great interest in many coherent imaging systems. What we believe to be a new phase unwrapping algorithm, is described and tested. The method starts from the fact that 2D wrapped phase distribution can be regarded as a response to two orthogonal 1D direction excitation signals. This suggests a cepstrum analysis to be implemented in the phase unwrapping problem. Experimental results both from the fringe projection profilometry and DENSE MRI also confirmed the validity of our approach. In fact, this proposed method is possible to attain a fast and practical phase unwrapping solution with enhanced noise robustness.