Dual-Mode Fiber Optofluidic Flowmeter With a Large Dynamic Range

Abstract

A dual-mode fiber optofluidic flowmeter with a large dynamic range of four orders of magnitude is developed. The sensing mechanism is based on the force balance on an optically trapped polystyrene microparticle. As the optical force is at piconewton level, the flowmeter is very sensitive with a lower detection limit of 10 nl/min. In the open-loop mode, the manipulation length is used as the sensing output and the flowmeter has an inverse sensitivity so that it has higher sensitivity at lower flow rate. In the closed-loop mode, the manipulation length is set constant and a feedback signal, tuning the laser power for the force balance, is used as the sensing output. The closed-loop mode is helpful for extending the upper detection limit of flow rate and also enhancing the sensitivity at higher flow rate. This paper introduces a new kind of high-performance optofluidic sensors based on optical forces.