Here, we demonstrate a multimode fiber Rayleigh-based sensor that can make quantitative strain measurements by tracking the amplitude of the backscattered speckle pattern recorded on a high-speed camera. The diversity of spatial modes provides sufficient information to recover both the magnitude and algebraic sign of the strain. Amplitude-measuring multimode fiber Rayleigh sensors have reduced sensitivity to laser phase noise, have higher thresholds for nonlinear effects, improving noise performance, and are completely immune to interference fading. The sensor presented here achieves pε/√Hz-level noise, over 10 kHz of bandwidth, and operates at a range of up to 2 km.
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