Differential Doppler flowmeters with single-mode fiber waveguides

A study was made of the characteristics of the operation of various modifications of a differential laser Doppler flowmeter with single-mode fiber waveguides in the transmission channel. An analysis was made of the influence of the polarization and spatial characteristics of radiation beams emerging from single-mode fiber waveguides on the structure of the probe field of such a flowmeter. A compact differential flowmeter utilizing the LP₁₁ waveguide mode was developed. The use of this flowmeter was demonstrated by measurements in a water stream.