Demodulation technique for 3-D tip clearance measurements based on output signals from optical fiber probe with three two-circle coaxial optical fiber bundles

In this work, we propose a new demodulation technique for three-dimensional (3-D) tip clearance measurements using the output signals acquired from three two-circle coaxial optical fiber bundles. This technique is based on the ratio of the difference in the signal intensities between any two sensing units of the optical fiber probe, and we derived the demodulation equations using the second-order Taylor expansion for a three-variable function. We verified the feasibility of the demodulation technique by experiments and demodulation error curves, which indicates that the method is viable for 3-D tip clearance measurements.