A high-sensitivity all-fiber temperature sensor based on a Sagnac interferometer is demonstrated by splicing a section of polarization maintaining fiber (PMF) between two sections of standard single mode fibers (SMFs). In this sensor, the SMF-PMF-SMF structure in the Sagnac loop is bent into a circle to enhance the sensitivity. The length and curvature of the PMF in the loop are investigated and can be optimized to further increase the temperature sensitivity of the sensor. Results show that the radius of the circle has an important effect upon temperature sensitivity due to the bend-induced birefringence variation of the PMF. The SMF-PMF-SMF structure bent into a circle with a radius of 30 mm exhibits a high-sensitivity temperature of 1.73 nm/℃. The sensor is provided with the advantages of easy fabrication, low-insertion loss, and high sensitivity, which may find potential applications in the field of high precision temperature measurement.

Photovoltaic power converters transform optical power into electrical power, which is inherently immune to RF, EMI, high voltage, and lightning effects. Capable of powering electronic circuitry directly over optical fiber in a wide variety of applications, this technology has been validated in industries such as electric power, communications, remote sensing and aerospace. From no more than a laboratory curiosity less than fifteen years ago, power-over-fiber, or photonic power, has established itself in thousands of industrial operations worldwide. Optical energy for pre-amplifiers or lowpower transmitters as well as switches and relays can be efficiently delivered through noise immune and non-conductive optical fiber. These advantages are also readily available for safe and arm applications since optical fiber is immune to electrical noise, magnetic fields and conduction of unexpected electrical currents. Since it is made from glass, a dielectric fiber is impervious to electromagnetic interference. High optical power is readily delivered through fiber, and conversion of optical to electrical energy at the remote site with efficient photovoltaic converters is routine.

A cost-efficient P-D fiber structure-based Sagnac loop sensor is proposed and experimentally demonstrated for measuring temperature and liquid refractive index (RI). The P-D structure is fabricated by fusion splicing a section of polarization-maintaining fiber (PMF) to a piece of multimode D-shaped optical fiber (MMDF). Then the P-D structure is built into a Sagnac loop using a 3dB coupler. The temperature and RI characteristics of the sensor are investigated experimentally. The results show that two resonant dips have different spectral responses of temperature and RI, which indicate that the sensor can realize simultaneous temperature and RI measurement. The high sensitivities of -1.804nm/°C and -131.49nm/RIU are achieved. The obtained resolutions of temperature and RI of the proposed sensor can reach 0.01°C and 2.46 × 10RIU, respectively. The proposed sensor has the potential application in biological and chemical fields.

A fibre loop mirror sensor is proposed and demonstrated for strain and temperature measurements in experiment. In these schemes, fibre loop mirrors are constructed with single-mode-multimode-polarization-maintaining-multimode-single-mode optical fibre (SMPMS) structures. The strain and temperature characteristics of the sensor, depending on the lengths of multimode fibre (MMF) and polarization-maintaining fibre (PMF), are studied in the experiment. The results indicate that PMF and MMF lengths have less impact on strain sensitivity but a remarkable impact on temperature sensitivity, which is consistent with the theoretical analysis. The best strain and temperature sensitivities of an SMPMS structure sensor can reach up to 39.0 pm/με and 2.366 nm/°C, respectively. The sensors have the merits of easy fabrication, cost-efficiency and high temperature sensitivity and are quite suitable for fields requiring high-precision measurement. This is an open access article under the terms of the Creative Commons Attribution-NonCommercial License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited and is not used for commercial purposes.

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