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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.

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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 broadband tunable orbital angular momentum (OAM) mode converter based on a helical long-period fiber grating (HLPFG) inscribed in a conventional single-mode fiber (SMF) is experimentally demonstrated. The proposed all-fiber OAM mode converter is based on the core-cladding mode dual resonance near the dispersion turning point (DTP). The converter can operate with a bandwidth of 303.9 nm @ −3 dB and 182.2 nm @ −10 dB, which is, as far as we know, the widest bandwidth for a conventional SMF. Furthermore, the bandwidth of the OAM mode can be dynamically tuned within a large dynamic range (>80 nm) by simply twisting the fiber clockwise (CW) or counterclockwise (CCW). The dynamic tunability of the bandwidth of the proposed OAM mode generator may find vital applications in large-capacity optical fiber communication systems.