Digital wavefront recording, reconstruction and 3D display
Date of Issue2009
School of Computer Engineering
In this report, we summarize the work we have done under the support of SUG 15/06: Digital wavefront recording, reconstruction, and 3D display. The importance of the project is from the fact that phase of optical wavefronts are more important in precision metrology, though we sense the amplitude of optical wavefronts every day. Thus the objective of the project is measure, analyze and display the phase. Throughout the investigation, we have the following achievements: 1. For phase measurement, a novel phase measurement method, frequency-shifting method was proposed. It only needs two fringe patterns, comparing with traditional phase-shifting technique which needs at least three fringe patterns. 2. For phase analysis, a spatially adaptive strategy for windowed Fourier transform was proposed and compared with the spatially fixed strategy and their respective advantages and disadvantages were revealed, which was useful for reliable phase analysis. 3. For phase display, we focused more on the phase unwrapping technique, which converts a discontinuous phase map to a continuous phase map and consequently the shape of wavefronts can be readily displayed. Before phase unwrapping, phase denoising is usually necessary. We for the first time compared many effective filters and surprisingly revealed that they were all equivalent. We also pointed out that a popular filter, sine/cosine average filter, is not reliable. We further worked on the windowed Fourier based phase unwrapping technique and found that it would not be affected by threshold, which greatly improves the robustness of the method. 4. Finally we pushed the work by one level higher: we unified windowed Fourier based fringe pattern analysis and digital image correlation from an optimization point of view. These two fields were isolated previously but we built a bridge between them and thus the researchers in two areas can communicate more effectively. The successful completion of the project and findings we achieved inspire us to a bolder ambition to ultimately solve the phase analysis problem: an accurate, robust and real-time fringe analysis tool.
DRNTU::Engineering::Electrical and electronic engineering::Optics, optoelectronics, photonics