A simple, compact, and highly sensitive optical fiber directional bend sensor is presented. This device consists of a lateral-offset splicing joint and an up-taper formed through excessive fusion splicing method. The lateral-offset splicing breaks the cylindrical symmetry of the fiber and defines a pair of directions along which the bending response of the Mach-Zehnder interferometer transmission spectrum is different and thus could be used for bending vector measurement. For a curvature range from -3 to 3 m(-1), the bending sensitivities at 1463.86 nm and 1548.41 nm reach 11.987 nm/m(-1) and 8.697 nm/m(-1), respectively.

High-order orbital angular momentum (OAM) modes, namely, OAM and OAM, were generated and demonstrated experimentally by twisting a solid-core hexagonal photonic crystal fiber (PCF) during hydrogen-oxygen flame heating. Leaky orbital resonances in the cladding depend strongly on the twist rate and length of the helical PCF. Moreover, the generated high-order OAM mode could be a polarized mode. The secret of the successful observation of high-order modes is that leaky orbital resonances in the twisted PCF cladding have a high coupling efficiency of more than -20  dB.

A miniaturized tip Fabry-Perot interferometer (tip-FPI) is proposed for high-temperature sensing. It is simply fabricated for the first time by splicing a short length of microfiber (MF) to the cleaved end of a standard single mode fiber (SMF) with precise control of the relative cross section position. Such a MF acts as a Fabry-Perot (FP) cavity and serves as a tip sensor. A change in temperature modifies the length and refractive index of the FP cavity, and then a corresponding change in the reflected interference spectrum can be observed. High temperatures of up to 1000 °C are measured in the experiments, and a high sensitivity of 13.6 pm/°C is achieved. This compact sensor, with tip diameter and length both of tens of microns, is suitable for localized detection, especially in harsh environments.

High-dimensional entanglement has demonstrated potential for increasing channel capacity and resistance to noise in quantum information processing. However, its distribution is a challenging task, imposing a severe restriction on its application. Here we report the first distribution of threedimensional orbital angular momentum (OAM) entanglement via a 1-km-long optical fibre. Using an actively-stabilising phase precompensation technique, we successfully transport one photon of a three-dimensional OAM entangled photon pair through the fibre. The distributed OAM entangled state still shows a fidelity up to 71% with respect to the three-dimensional maximal-entangledstate (MES). In addition, we certify that the high-dimensional quantum entanglement survives the transportation by violating a generalised Bell inequality, obtaining a violation of ∼ 3 standard deviations with I3 = 2.12 ± 0.04. The method we developed can be extended to higher OAM dimension and larger distances in principle. Our results make a significant step towards future OAM-based high-dimensional long distance quantum communication. *

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