Analyses of micro-fluid flow in a hollow core fiber based on optical interference

In micro-fluidic devices, a small amount of fluid flows along the pre-determined channels to be chemically analyzed, or to activate mechanical/optical functions. Such devices have been extensively used in biochemistry, medical science, and optical engineering. One of the essential techniques in micro-fluidics is to monitor the fluid flow with high accuracy. Currently the flow can be analyzed using hot-wire anemometer, laser Doppler velocimeter[1], or through direct observation using microscopes. In this work, we used optical interference between the two reflected beams, one from the fixed point and the other from the front-end of the fluid to measure velocity and position of the fluid. We could also estimate the curvature of the fluid surface since the intensity of the reflected beam is largely dependent on the curvature. A hollow core fiber(HCF, or photonic bandgap fiber) with a hole diameter of 20 μm was used instead of ordinary capillary tube for low loss optical propagation through the fluid channel. In this preliminary study, mercury was used for the fluid for high reflectivity.