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 microstrain. The high sensing properties is achieved through 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 repeatability for 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.

A high linear sensitivity fiber temperature and vector curvature sensor based on dual-core photonic crystal fiber was designed and implemented. Theoretical and experimental results show that, the temperature sensing sensitivity at 30 °C–510 °C is 61.68 pm °C ⁻¹ , and the linear fitting coefficient is up to 0.998. The sensor can realize high linear (0.997) vector bending sensing on the plane where the two cores are located, and the sensing sensitivity is 3262.57 nm mm and −1608.56 nm mm respectively. Compared with fiber sensors based on complex and fragile structures, it has higher mechanical strength, wider sensing range, and simple preparation process.