Demodulation error and influencing factor of three-wavelength digital phase demodulation method

This paper introduces the traditional demodulation method of Fabry-Perot (F-P) sensors, and systematically derives the demodulation principle of three-wavelength digital phase demodulation method using extrinsic Fabry-Perot interferometer (EFPI) sensors. Meanwhile, simulation method has been used to analyze the demodulation error of three-wavelength phase demodulation method. The results indicate that the phase deviation from an orthogonal relationship is the most important influencing factor limiting the demodulation. In order to ensure that demodulation error is less than 15 nm, the cavity length change should be within the range of 2 μm at the orthogonal cavity length. Three independent laser light sources have been used to do the experiment. The results show that when the cavity length changes within 1 μm from orthogonal cavity length, the error of the demodulation cavity length is less than 12 nm, and at the same time the repeatability error of the demodulation is less than 10 nm, which means that demodulation has good stability.