All-Fiber Pulse-Train Optical Frequency-Domain Interferometer for Dynamic Absolute Distance Measurements of Vibration

In this paper, we propose an all-fiber co-axial optical frequency-domain interferometer (OFDI) in a pulse-train mode with a sample rate of 9 kHz for measuring the vibrations in an internal structure without any contact. It was subjected to a range of 4.555 mm and had an accuracy level of 0.006 mm, as confirmed by a linear motion experiment. Due to the precise time synchronization for reducing the background light leakage and suppressing the dynamic fuzziness, the proposed OFDI could realize the dynamic absolute distance measurements of the vibration process under harmonic excitation with frequencies ranging from 200 Hz to 1800 Hz. The characteristic parameters of vibration could be analyzed using the acquired distance results. Furthermore, the OFDI system obtained the frequency conversion as the time under anharmonic periodic excitation with a sweeping rate of 3600 Hz/s. The measurement performance for the vibration velocity compared with the displacement interferometer system for any reflector (DISAR) was demonstrated in a harmonic excitation experiment. The proposed method expands the application of all-fiber OFDI technology from static to dynamic scenes.