Doppler Effect-Based Optical Fiber Vibration Sensor Using Frequency-Shifted Interferometry Demodulation

A novel optic-fiber vibration sensing system based on frequency-shifted interferometry (FSI) is proposed and demonstrated in this paper. The sensor is based on the phenomenon that the light frequency transmitted through a segment of bent fiber can be Doppler shifted by vibration. The Doppler frequency shift is measured using FSI demodulation. Compared to traditional fiber Bragg grating vibration sensor, the proposed sensor is easy to fabricate, of low cost and without directional dependency. The application of FSI demodulation allows for custom tailoring of measurement sensitivity, and has superior signal stability due to its same-path interference nature. The measured Doppler frequency shift using the FSI system agrees well with the calculated one, derived from strain measurements. The results show that the system has a high sensitivity and wide frequency range, limited only by the excitation apparatus used in the experiment.