Compact Laser-Diode Instrument for Flow Measurement

We demonstrate a flow-meter sensor using a bare laser diode (LD) as a self-mixing interferometer and no additional lens nor optical component. The diode is placed directly on the edge of the duct, exploiting the natural laser divergence. The flow measurement is based on the Doppler shift induced by the scattering particles inside the fluid and read by the self-mixing effect inside the LD. The proposed approach has been modeled by a numerical simulator in order to find the best signal processing algorithm. A set of measurements on blood proves good performances as a flow meter, while simulations confirm the system robustness to mechanical misalignments and changes in liquid properties.