Single-arm Self-mixing Superluminescent Diode Interferometer for Flow Measurements

Laser-diode self-mixing interferometry is a noncontact technique widely used both in industries and laboratories. In this paper we propose to extend the self-mixing approach to low-coherence sources such as superluminescent diodes. In particular, we present a fiber-based common-path interferometer exploiting a single mode pigtailed super-luminescent diode. The developed measuring system has been demonstrated to be able to directly measure the flow in pipes. To the best of our knowledge, it is the first time that flow measurements have been performed by a single-arm self-mixing pigtailed super-luminescent-diode. The measuring system exploits the Doppler interference pattern produced by the light back-reflected from the inner facet of the pipe wall and the light back-diffused by the moving particles. Then, the use of a low-coherence source allows to measure the velocity of the scattering particles in a fixed and well defined region located close to the pipe wall, thus providing good robustness to variations of scatterers concentration and allowing to easily estimate the flow under the laminar flow assumption. Experimental results demonstrated a high linearity (Pearson coefficient of about 99%) and sensitivity of about 16.62±1.1 cm−3, with flows ranging from 1 cm3/s to 15 cm3/s and scatterers volume concentration ranging from 0.015% to 0.36%.