Optical feedback interferometry sensing technique for flow measurements in microchannels

Abstract

The phenomenon of optical feedback interferometry (OFI) or self-mixing effect in a laser is used to design non-invasive and self-aligned sensors, requiring only few optical elements and simple to implement. This type of sensor is used to measure the displacement, velocity or position of cooperative targets (reflective or strongly scattering targets). In this study, this phenomenom is applied to the measurement of fluid flow profile in microchannels. The low cost and versatility of optical feedback sensors are of great interest in biomedical and chemical industry as well as research in fluid mechanics. Based on studies in macro-channels, we proposed first a theoretical model of OFI in a laser diode when the target consists of moving particles suspended in a liquid. Based on this model, we then studied experimentally the impact of the sensor’s sensing volume and the type of particles (size and concentration) on the OFI signal. We then proposed signal processing methods for calculating the fluid flow rate, as well as the local velocity at any point in a microchannel. These preliminary studies allowed us to reconstruct the flow profile of different liquids flowing in a circular channel of 320μm diameter. Finally, we compared the performance of the sensor developed in this thesis with a sensor based on the Dual-Slit technique, which has been already validated for microchannels, by measuring the flow profile in a rectangular shaped channel (100x20µm).