Vector velocimetry by using fiber-optic low coherence interferometers

A new velocimetry using the four probing points system consisting of fiber-optic low-coherence interferometers are proposed and demonstrated. The proposed velocimetry is capable of measuring simultaneously the 3-D velocity vector (absolute velocity and the velocity direction). The velocity vector distribution along depth can also be measured in the present method by scanning the mirror positions in the reference arms. Moreover, the 3-D velocity vector distribution can be measured by sweeping the mirror position for z-direction distribution and by moving the fiber probes for x- and y-direction distribution. The high spatial resolution of the present method enables us to apply the present method to sensing for velocity vector distributions of a boundary layer in liquid flow or of a vortex flow, and of a living body, which are very important in the field of fluid mechanics and the practical application. It is very difficult in conventional methods to measure the velocity vector in these application areas.