Direct velocity sensing of flow distribution based on low-coherence interferometry

A new sensing method for measuring flow velocity distribution directly 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 fast-Fourier-transform processor used and is estimated to be 1.4 x 10(-4)-14 m/s. The depth position can be adjusted with an accuracy of approximately 30 mu m, which is determined by the coherence length of the light source. (C) 1999 Optical Society of America [S0740-3232(99)02208-5].