Brillouin-Scattering Induced Noise in DAS: A Case Study

Area of Science:

• Optics and Photonics
• Sensing Technology

Background:

• Spontaneous Brillouin scattering (SpBS) is an intrinsic phenomenon in optical fibers.
• SpBS contributes to noise in distributed acoustic sensing (DAS) systems.
• Understanding SpBS noise is crucial for improving DAS performance.

Purpose of the Study:

• To analyze spontaneous Brillouin scattering (SpBS) as a noise source in distributed acoustic sensors (DAS).
• To quantify the noise power induced by SpBS.
• To investigate methods for mitigating SpBS noise in DAS.

Main Methods:

• Experimental analysis of SpBS intensity fluctuations.
• Determination of the probability density function (PDF) of the SpBS Stokes wave intensity.
• Estimation of SpBS noise power relative to Rayleigh backscattering.
• Noise composition analysis for different spectral configurations.
• Implementation of an asymmetric Mach-Zehnder interferometer (MZI) for SpBS rejection.

Main Results:

• SpBS intensity fluctuations increase noise power in DAS.
• The PDF of spectrally selected SpBS Stokes wave intensity follows a negative exponential distribution.
• SpBS noise power is approximately 18 dB lower than Rayleigh backscattering power.
• SpBS noise is identified as the dominant noise source in the analyzed DAS configurations, exceeding thermal, shot, and phase noises.
• Rejection of SpBS waves at the photodetector input reduces noise power.

Conclusions:

• Spontaneous Brillouin scattering is a significant noise contributor in DAS.
• Rejecting SpBS waves, especially for broadband photodetectors used with short pulses, is an effective strategy to reduce noise.
• The use of an asymmetric Mach-Zehnder interferometer demonstrates a practical method for SpBS noise mitigation.