“Bellows spring-shaped” ultrasensitive fiber-optic Fabry-Perot interferometric strain sensor

All-silica fiber-optic Fabry-Perot strain sensor is rapidly gaining widespread adoption in many fields due to its compact structure, low cost and immunity to electromagnetic interference. However, the conventional configuration suffers from low sensitivity due to the limitation of its inherent structure feature. In this paper, we demonstrate an ultrasensitive fiber-optic Fabry-Perot interferometric strain sensor based on silica bellows spring structure. Utilizing the cascaded microbubbles, the sensitivity of the single-microbubble sensor is enhanced up to 203.8 pm/με and that of the cascaded two-microbubble sensor reaches 518.8 pm/με. The sensitivity is reinforced by 5-to-12 folds compared with the highest level ever reported, which could also be multiplied by increasing the microbubble number. The temperature-induced strain error is much low, less than 0.01 με/°C, showing great thermal stability and high-temperature application potential. Moreover, the strain sensor also provides high-quality spectrum, controllable free-spectral range and low cost.