Thin-Fiber-Based Fabry–Pérot Cavity for Monitoring Microfluidic Refractive Index

We report an all-fiber miniature exposed Fabry-Pérot (F-P) cavity microfluidic refractometer by splicing an ultrashort segment of thin fiber with standard single-mode fiber with large off-center alignment. Theoretical investigations of dynamic range and sensitivity issues for the proposed fiber sensors are carried out. The exposed F-P cavity can provide excellent interaction between embedded gas/liquid with guided light, with a high sensitivity of 1086 nm/RIU at ~1550 nm within the refractive index (RI) range from 1.332 to 1.3565. Meanwhile, the exposed F-P cavity structure is insensitive to temperature fluctuation. The simple and cheap fabrication method, together with ultracompact package, stable operation, and low-temperature cross-sensitivity, verify that it has great potential for microfluidic RI sensing for chemical, biological, and medical applications.