Fluidic Flow Measurement Using Single Mode-Multimode-Single Mode Optical Fiber Sensor

The measurement of flow in fluidic channels is an essential task required for the proper operation of devices in many interesting applications. In this work, an optical fiber sensor based on a single mode - multimode - single mode (SMS) fiber structure is used to measure the flow in a millimeter-sized Polydimethylsiloxane (PDMS) fluidic channel. The measurement is based on the phenomena of vortex shedding, where the immersed fiber section acts as an obstructing strut. The sensing principle assumes slight fiber bending with vortex shedding, resulting in intensity variations of the light transmitted through the fiber sensor. To the best of our knowledge, this is the first time modal interference in an SMS fiber structure is explored for flow detection in a microfluidic device. The flow-related shedding frequency was detected through intensity variations of the transmitted light at a suitable laser wavelength. The linearity of the detected frequency with flow rate is confirmed over the investigated flow range with high R-2 values up to 99%. The frequencies detected are compared to the theoretically expected frequencies based on the theory of vortex shedding past a rigid strut. Nevertheless, their relation to the flow velocity is found to deviate in slope from that of the theoretical relation, which could be due to the interaction of the flow with the flexible optical fiber shedding strut. The good linearity of this sensor makes it a promising component for macro and microfluidic flow measurement in many applications.