Optical fiber sensor based on upconversion luminescence for synchronous temperature and curvature sensing.

A multifunctional optical fiber sensor based upconversion luminescence (UCL) for synchronous temperature and curvature sensing was proposed. The sensor was fabricated by assembling UCL nanoparticles doped by rare earth (RE) ions in polydimethylsiloxane (PDMS) materials. Temperature measurements were achieved through the fluorescent intensity ratio (FIR) technique with the dual green UC luminescence generated. The fabricated sensor provided the temperature sensitivity of 714.82 K-1 with excellent linearity (R2=0.997) at a temperature range of 303 to 423 K. In the lower temperature region, temperature measurement based on the FIR technology is almost independent on the fluorescence intensity of a 525 nm emission peak. Hence, deformation produced by the sensor through bending results in detectable and reversible changes in its reflected light, allowing the curvature to be simultaneously measured. The sensor can monitor temperature and curvature simultaneously, providing a new optical alternative for multi-parameters monitoring in the future.

Ultra-Sensitive Fiber Refractive Index Sensor with Intensity Modulation and Self-Temperature Compensation.

In this paper, a novel in-line modal interferometer for refractive index (RI) sensing is proposed and experimentally fabricated by cascading single-taper and multimode-double- cladding-multimode (MDM) fiber structure. Owing to evanescent field in taper area, the ultra-sensitive and linear intensity-responses to the varied surrounding RI are gained in both single- and double-pass structures. Moreover, the crosstalk from temperature can be effectively discriminated and compensated by means of the RI-free nature of MDM. The experimental results show that the RI sensitivities in single- and double-pass structures, respectively, reach 516.02 and 965.46 dB/RIU (RIU: refractive index unit), both with the slight wavelength shift (~0.2 nm). The temperature responses with respect to wavelength and intensity are 68.9 pm°C-1/0.103 dB°C-1 (single-pass structure) and 103 pm°C-1/0.082 dB·°C-1 (double-pass structure). So the calculated cross-sensitivity of intensity is constrained within 8.49 × 10-5 RIU/°C. In addition, our sensor presents high measurement-stability (~0.99) and low repeatability error (<4.8‱). On account of the ~620 µm size of taper, this compact sensor is cost-efficient, easy to fabricate, and very promising for the applications of biochemistry and biomedicine.