Axial clearance measurement method based on wavelength division multiplexing with all-fiber microwave photonic mixing

Rotor-stator axial clearance plays a pivotal role in ensuring the safety and efficiency of major rotating machinery. This paper introduces an innovative clearance measurement method based on wavelength division multiplexing (WDM) combined with all-fiber microwave photonic mixing. The method is distinguished by large measurement range, high accuracy and low drift. The WDM-based common optical path structure is established. A comprehensive theoretical model of axial clearance drift determined by wavelength and temperature is developed based on the thermo-optic effect of optical fiber material. To efficiently separate measurement and reference light at the probe, the optical design for a compact optical bandpass filter (OBPF) fiber sensor probe is proposed. The performance of the method is substantiated by simulations and experiments. The results demonstrate an accuracy of better than 2.8µm over a 23.5 mm range, surpassing existing methods. The method's capability to mitigate temperature-induced drift is further confirmed through high-temperature drift and comparative experiments.