Forward Brillouin Scattering for Bubble and Flow Interruption Detection Toward Microscale Liquid Systems

Identification of bubbles and flow interruptions in microscale liquid systems is a significant subject. We propose an innovative method using forward Brillouin scattering (FBS) in optical waveguide to accurately identify gas and liquid phase states in these systems. The feasibility was demonstrated through the utilization of optical fibers. Our study explains how FBS facilitates phase state identification and introduces a multiplexing scheme along with highly efficient single-end demodulation capability. We explained the relationship between FBS intensity and external materials. The proposed sensing units facilitate seamless cascading, allowing for precise differentiation and positioning based on scattering frequency. In gas-phase environments, alert signals with specific frequencies can be detected in narrow bands and exhibit strong intensity. Additionally, our demodulation system provides single-end access to sensing units at the millimeter level, significantly surpassing current schemes in terms of spatial recognition capability, especially compared to those with multiplexing and positioning functions. Experimental results confirm the effectiveness of our method in monitoring both static and dynamic bubbles as well as flow interruption patterns. To our knowledge, the proposed sensor provides the most advanced FBS spatial recognition and is the first to achieve single-end millimeter-level FBS sensing.