Abstract
Brillouin based fiber sensors are susceptible to a range of technical and environmental noise sources that can degrade the sensor performance or introduce unacceptable levels of crosstalk. Here, we introduce a new measurand that combines information from the complex Stokes and anti-Stokes interactions to extract the Brillouin frequency shift while suppressing noise and crosstalk originating from fluctuations in the power, frequency, or polarization state of the pump and probe beams. We then present a modified slope-assisted Brillouin optical time domain analysis (BOTDA) architecture capable of simultaneously recording the gain, loss, and phase associated with both the Stokes and anti-Stokes interactions. We experimentally confirm that the sensor is able to reject noise due to laser frequency jitter, intensity noise, or polarization fading and is immune to crosstalk due to effects such as pump depletion. By suppressing these noise sources, the sensor is able to achieve a minimum detectable strain of only 15.6 nε/Hz1/2 in ∼1 km of fiber with 4 m spatial resolution and a sensor bandwidth of 25 kHz, representing a significant noise improvement compared to state-of-the-art BOTDA systems.
Highlights
Brillouin based fiber optic sensors are attractive due to their ability to provide absolute strain measurements using a standard telecom fiber
We introduce a new measurand that combines information from the complex Stokes and anti-Stokes interactions to extract the absolute Brillouin frequency shift (BFS) while rejecting the majority of noise sources that can limit the performance of standard SA-Brillouin optical time domain analysis (BOTDA) type systems
While SA-BOTDA systems that only probe the Stokes interaction cannot differentiate between a change in the Brillouin frequency and a change in the laser frequency, we demonstrated that adding an anti-Stokes probe provides additional information that can disambiguate these two effects
Summary
Brillouin based fiber optic sensors are attractive due to their ability to provide absolute strain measurements using a standard telecom fiber. Researchers showed that measuring the ratio of the phase to gain provided even better immunity to pump power fluctuations while increasing the dynamic range of the sensor.[12,23] A variety of multiplexing techniques were proposed to further increase the dynamic range of SA-BOTDA systems.[8,10,11,14,15,24] We recently presented a scheme that combined the interactions between the Stokes and anti-Stokes probes on a single detector to suppress dynamic strain induced crosstalk.[19] While these efforts showed that many of the challenges associated with SA-BOTDA systems are tractable, a single system capable of mitigating each of these sources of noise and crosstalk remains to be demonstrated. This noise level represents a significant improvement compared with state-of-the-art BOTDA sensors, and as such, we expect this technique to be broadly useful in typical Brillouin based applications
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