Optical fiber strain sensor with high precision and extended dynamic range based on a coupled optoelectronic oscillator

Abstract

We have proposed and experimentally demonstrated an optical fiber strain sensor with high precision and extended dynamic range based on a coupled optoelectronic oscillator (COEO). The COEO is a combination of an OEO and a mode-locked laser, sharing one optoelectronic modulator. The feedback between the two active loops makes the oscillation frequency equal to the mode spacing of the laser. It is equivalent to a multiple of the natural mode spacing of the laser, which is affected by the applied axial strain to the cavity. Therefore, we can evaluate the strain by measuring the oscillation frequency shift. Higher sensitivity can be obtained by adopting higher frequency order harmonics owing to the accumulative effect. We carry out a proof-to-concept experiment. The dynamic range can reach 10000 με. Sensitivities of 6.5 Hz/με for 960 MHz and 13.8 Hz/με for 2700 MHz are obtained. The maximum frequency drifts of the COEO in 90 mins are within ±148.03 Hz for 960 MHz and ±303.907 Hz for 2700 MHz, which correspond to measurement errors of ±22 με and ±20 με. The proposed scheme has the advantages of high precision and high speed. The COEO can generate an optical pulse whose pulse period is influenced by the strain. Therefore, the proposed scheme has potential applications in dynamic strain measurement.