Double-Sphere Tapered Fiber RI, Temperature, and Strain Sensor Based on Micro-Spherical Mode Controller

A double-sphere tapered fiber interferometer based on micro-spherical mode controller has been proposed and demonstrated to have high sensitivity and linearity to refractive index (RI), temperature and micro-strain. The high sensing properties is achievedthrough high order modes control based on microsphere. Theoretical analysis and experimental results show that designed microsphere on tapered fiber can excite appropriate high-order modes which enhance interferences to improve sensing performance. The sensor has a high linear, low temperature cross RI sensitivity of ~-285.47 nm/RIU. The UV-cured polymer coated DSTF structure is also demonstrated in temperature and micro-strain sensing. The temperature sensitivity reaches ~1.69 nm/°C, which is ~340 times higher than the uncoated structure, and the strain sensing sensitivity reaches ~84.02 pm/με which is about ~40 times than the ordinary fiber strain sensors. The sensor has high linearity (fitting coefficient is up to 0.999), excellent thermal stability and repeatabilityfor RI temperature and strain. Benefited from the advantages of simple preparation method, low cost and compact structure, this inter-mode interference-based fiber sensor is expected to be one of the ideal instruments for high precision RI, temperature and strain sensing fields.