Fiber-Optic Low Coherence Velocimetry by Detecting Interference Fluctuations

Yoh IMAI  Kazuhiro TANAKA  

IEICE TRANSACTIONS on Electronics   Vol.E83-C    No.3    pp.423-427
Publication Date: 2000/03/25
Online ISSN: 
Print ISSN: 0916-8516
Type of Manuscript: Special Section PAPER (Special Issue on Optical Fiber Sensors)
Category: Distributed Sensing
optical fiber sensing,  optical distributed velocimetry,  low-coherent interferometry,  

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A new sensing method for measuring directly flow velocity by using low coherence interference techniques is proposed and demonstrated. In this method, a temporally fluctuating signal, not the Doppler frequency shift, is detected. Theoretical analysis shows that a spectrum of light backscattered from a particle takes a Gaussian form whose width is simply proportional to the flow velocity. The measured velocity is in good agreement with the actual flow velocity derived from the flow rate. The dynamic range of this sensing method is governed by the frequency range of the FFT processor used and is estimated to be 1.4 10-4 14 m/s. The depth position can be adjusted with an accuracy of approximately 30 µm which is determined by the coherence length of the light source. The velocity distribution along the depth is easily measured by changing mechanically the length of the reference arm in the low coherence interferometer.