Abstract
A dual-mode optofluidic flow rate sensor with a large dynamic range of 4 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 very small, the flow rate sensor is very sensitive. In the open-loop mode, the manipulation length is used as the sensing signal. The sensor has an inverse sensitivity, that is, the manipulation length decreases as the flow rate increases, so that it has high sensitivity at low flow rate. In the closed-loop mode, the manipulation length is set to be constant and a feedback signal to tune the laser power for force balance is used as the sensing signal. The closed-loop mode is helpful for extending the upper limit of flow rate and also enhancing the sensitivity at high flow rate.
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