Pollutions caused by heavy metals has become a wordwide concerned issue. Herein, CsPbBr3 perovskite quantum dots are used as fluorescent probe for selective detection of copper ions in organic phase with a limit of detection (LOD) down to 0.1 nM.

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We demonstrate the evolution characteristics of laser linewidth in accordance to Rayleigh backscattering (RBS) signal accumulated from different lengths of the RBS fiber. An ultra-narrow-linewidth fiber laser operating in single longitudinal mode has been obtained. The output linewidth is approximately 210 Hz and the side-mode suppression ratio is as high as ∼60 dB provided the length of the RBS fiber is set to be 5 km. The theoretical prediction suggests linewidth of tens of Hertz could be achieved provided the experimental setup is further optimized and the temperature control device is introduced.

In this Letter, we demonstrated an intensity-modulated directional torsion sensor based on an in-line Mach-Zehnder interferometer in single-mode fiber. A non-circular symmetric perturbation is created to excite non-circular symmetric cladding mode and then interference with the core mode at the second perturbation. An initial rotation angle is designed between two perturbations for the purpose of discriminating the torsion direction. Both experimental and theoretical results enforce that the spectral peak/dip turns to be the dip/peak when the fiber is twisted from the counter-clockwise to the clockwise direction. Benefiting from the reversal between peak and dip, an intensity-modulated directional torsion sensor is realized in the range from -50  rad/m to 50 rad/m with a sensitivity of 45.3%/(rad/cm).