Phase extraction of non-stationary interference signal in frequency scanning interferometry using complex shifted Morlet wavelets

Frequency scanning interferometry (FSI) with an external cavity diode laser is an effective technique for measuring the absolute distance of a target. However, because of the nonlinearity in optical frequency scanning, an interference signal becomes a non-stationary chirp signal, which is a critical issue to extract the phase of the interference signal for improving the accuracy of FSI. In this paper, a method for extracting the phase using complex shifted Morlet wavelet is proposed to accurately track the instantaneous phase of the chirp signal, and the selection of the wavelet parameters is also derived. The method is verified to be effective and stable by performing simulations and experiments. The experimental results demonstrate that the relative error of the phase extraction in the fractional part of interference signal is <1.5%;, and the standard deviation of absolute distance measurement is <1.69 μm