Mathematical Modeling of Heterodyne-Type Laser Doppler Velocimeter Operating Via Long Optical Fiber Guide

We present a mathematical model of the signal and noise components in the heterodyne-type laser Doppler velocimeter (LDV) which operates via long optical fiber guide. Our model accounts for laser power output, the length of the optical fiber guide, its absorption, the Rayleigh and Brillouin scattering in the optical fiber guide, and the photo detector parameters. The scattering properties of the moving particles in the liquid or gas flow which is accessed by the LDV are accounted for by an integral scattering coefficient. We show that the Rayleigh and Brillouin scattering in the optical fiber are the principal noise sources that corrupt the signal-to-noise ratio of the present LDV. The numerical examples show that Ae SNR can be as low as 0 dB in the case of the typical optical fibers of a length of several kilometers