Radio Frequency FBG-Based Interferometer for Remote Adaptive Strain Monitoring

A radio frequency (RF) optical fiber interferometer based on dual-fiber Bragg grating is proposed for a few to tens of kilometers distance remote measurements. The interference spectrum is observed in the microwave domain by sweeping the frequency using a network analyzer. The wavelength-difference variation is naturally transferred to the RF phase-difference change after the long round-trip of the optical carriers shifting the microwave interference pattern. The sensor exhibits important advantages of easy multiplexing, stability against random perturbations, self-adaptation to temperature, and mostly importantly, a potentially much higher sensitivity compared with common wavelength-modulated optic sensors. A measurement of a strain-turned grating was accomplished with a ~6.5-km long single-mode fiber, where a high maximum sensitivity of 53.57 kHz/με was realized, which can easily be further improved by more than two orders of magnitude through various low-cost fiber dispersion components.