Novel OPD demodulation method based on intercepted spectrum with an integral period

A cavity length demodulation method, which is dedicated to solving the frequency spectrum leakage and barrier effect of FFT analysis, is proposed. The signal interception is adopted to improve the demodulation effect, and the curve fitting method is applied to find a more accurate characteristic frequency of the spectrum. Compared with the pre-setting additional phase method, the demodulation performance is not influenced by the change of the additional phase, and the lower limit of cavity length can be extended to 50μm. The simulation and experiment verification are carried out to evaluate the performance of the proposed method. The strain stability experiment indicates that the proposed method has a cavity length demodulation resolution of 1.21 nm at the length of about 131μm. The proposed method is promising for the application in the situation of the short cavity and indeterminate additional phase difference.