Multi-frequency phase unwrapping algorithms (MFPUAs) are among the most robust and efficient phase unwrapping methods, and hence widely adopted in various optical measurement techniques, such as fringe projection profilometry, interferometry, and so on. However, if they are not well designed, or the measurement condition is poor, fringe order error (FOE) will be triggered during the phase unwrapping, which will result in phase unwrapping error. This paper is for coping with FOE without consuming additional fringe patterns for phase unwrapping. Firstly, a parameter called fringe order inaccuracy (FOI) which is applicable to the representative MFPUAs is defined. Secondly, FOI is employed to help quantify the possibility of the occurrence of FOE. Lastly, a fast FOE correction method is proposed with aid of FOI. Experiments validate that the proposed method contributes to suppressing FOE while keeps the efficiency of MFPUA.
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.