Microbubble-Based Fiber Optofluidic Interferometer for Sensing

A fiber optofluidic interferometer based on an optical microbubble-on-tip (μBoT) structure is developed. The generation process and sensing mechanism of this μBoT sensor are very different from traditional optical fiber sensors. The μBoT is a hybrid solid/liquid/gas microstructure generated by heating a fiber tip with laser and can be easily regenerated with low cost and good repeatability. Carbon nanotube film is optically deposited on the fiber end face to increase the laser absorption, thus enhances the efficiency of the μBoT generation. The diameter of the μBoT interferometer increases with time, leading to a decrease in the free spectral range (FSR). By measuring the FSR, the temperature and flow rate sensing are demonstrated. A temperature sensitivity of -1146 pm/°C is achieved, which is two orders of magnitude higher than that of the widely used fiber Bragg gratings. A lower limit of detection of 10 nL/min and a resolution of 0.03 nL/min for the flow rate sensing are obtained, which is better than that of the state-of-the-art microfluidic flowmeters. Our study will open a door to the development of novel reconfigurable fiber optofluidic sensors.