Additive-to-multiplicative moire fringe transition in simultaneous dual-wavelength interferometry

Simultaneous dual-wavelength interferometry (SDWI) could extend the measured range of each single-wavelength interferometry, and has higher efficiency when the two single wavelengths work simultaneously. However, the directly measured phase demodulation at the long synthetic wavelength (lambda(S)) from the generated moire fringe patterns in SDWI is rather arduous. To reduce the difficulty of the processing for the moire fringe patterns, a synthetic wavelength temporal phase retrieval method (STP) with the pi/(2k) phase shift at lambda(S) was proposed in this paper. By the additive-to-multiplicative moire fringe transition, the synthetic-wavelength interferometry information exists in the form of the superposition with other wavelength information. And then for the longer separation distance of the phase lobes in spectrum, the synthetic-wavelength spectrum in STP method could be filter out more easily than traditional temporal Fourier transform (FT) method. After a low-pass filtering in the spectrum of the multiplicative moirefringe intensity and adopting the pi/(2k) phase shift at lambda(S), the synthetic-wavelength phase is retrieved by the conventional phase-shift algorithm from the obtained synthetic-wavelength phase-shift interferograms with the interval of pi/2 phase shift. Compared with the spatial FT method with the introduction of spatial carrier, STP method releases the restriction of spatial carrier for spectrum separation and the requirement of quadratic polar coordinate transform for the circle carrier. Finally, the feasibility and applicability of the STP method are verified using simulation and experimental results.