We have proposed and demonstrated a Michelson interferometer-based fiber sensor for detecting acoustic emission generated from the partial discharge (PD) of the accessories of a high-voltage cable system. The developed sensor head is integrated with a compact and relatively high sensitivity cylindrical elastomer. Such a sensor has a broadband frequency response and a relatively high sensitivity in a harsh environment under a high-voltage electric field. The design and fabrication of the sensor head integrated with the cylindrical elastomer is described, and a series of experiments was conducted to evaluate the sensing performance. The experimental results demonstrate that the sensitivity of our developed sensor for acoustic detection of partial discharges is 1.7 $\mathrm{rad}/\left(\mathrm{m}\cdot \mathrm{Pa}\right)$ . A high frequency response up to 150 kHz is achieved. Moreover, the relatively high sensitivity for the detection of PD is verified in both the laboratory environment and gas insulated switchgear. The obtained results show the great potential application of a Michelson interferometer-based fiber sensor integrated with a cylindrical elastomer for in-situ monitoring high-voltage cable accessories for safety work.

Atomic layer deposition (ALD) technology is introduced to fabricate a high sensitivity refractive index sensor based on an adiabatic tapered optical fiber. Different thickness of Al₂O₃ nanofilm is coated around fiber taper precisely and uniformly under different deposition cycles. Attributed to the high refractive index of the Al₂O₃ nanofilm, an asymmetry Fabry-Perot like interferometer is constructed along the fiber taper. Based on the ray-optic analysis, total internal reflection happens on the nanofilm-surrounding interface. With the ambient refractive index changing, the phase delay induced by the Goos-Hänchen shift is changed. Correspondingly, the transmission resonant spectrum shifts, which can be utilized for realizing high sensitivity sensor. The high sensitivity sensor with 6008 nm/RIU is demonstrated by depositing 3000 layers Al₂O₃ nanofilm as the ambient refractive index is close to 1.33. This high sensitivity refractive index sensor is expected to have wide applications in biochemical sensors.

Vortex beams have attracted much attention in recent years due to unique features of the phase or polarization singularity in the center part of beams. Various applications have been explored by the vortex beams including optical communication, optical tweezer, etc. Especially, the vortex beams for optical sensing applications have emerged. Compared with the traditional Gaussian beams, the vortex beams enable the optical sensing with the degree of freedom by controlling the spin and orbital phase and polarization. In this review article, we have discussed the theory of polarization and phase vortices, and then summarized the vortex beam generation in optical fiber and their sensing applications. It is hoped that the article can intrigue further research interest and development in fiber vortices for sensing applications.

We demonstrate a method to truly measure the phase change originated from external vibration by heterodyne phase-sensitive optical time-domain reflectometer ($\varphi$-OTDR). The method of differential phase between sections of a sensing fiber is explored. In order to truly measure the phase change induced by external vibration, we point out that such sections of the fiber to calculate differential phase must cover at least the whole vibration region together with a section of fiber spaced by a pulse duration. The resultant differential phase is theoretically found to be twice the value of the real phase induced by external vibration. We further experientially investigate a distributed sensor with a sensing fiber of 41.2 km based on $\varphi$-OTDR system. The experimental results are well consistent with the simulation results, which provides a general guidance for quantitative phase measurement of the external excitation such as slow variations based on heterodyne $\varphi$-OTDR technique.

The discovery of graphene has intrigued the significant interest in exploring and developing the two‐dimensional layered materials (2DLMs) for the photonics application in recent years. Unlike the isotropic graphene, a number of 2DLMs possess the in‐plane anisotropic crystal structure with low symmetry, enabling a new degree of freedom for achieving the novel polarization‐dependent and versatile ultrafast photonic devices. In this review article, we focus on the typical anisotropic 2DLMs including BP, ReS ₂ , ReSe ₂ , SnS, and SnSe and summarize the recent development of these anisotropic 2DLMs in the pulsed laser and the optical switch applications. First, we introduce the fabrication methods as well as the material characterization of the anisotropic 2DLMs by analyzing the polarized Raman configuration. Second, we discuss the anisotropic nonlinear optical properties of the anisotropic 2DLMs and concentrate on the anisotropic nonlinear absorption response. Next, we sum up state of the art of the anisotropic 2DLMs in the application of pulse lasers and optical switches. This review ends with perspectives on the challenge and outlook of the anisotropic 2DLMs for ultrafast photonics applications.

We have proposed a magnetic field sensor using orbital angular momentum (OAM) $ {L}= {\pm }1$ modes, corresponding to right- and left- handed circular polarization, respectively, in a vortex fiber that supports propagation of these modes. These two circularly polarized OAM modes produce a phase difference under the Faraday effect, which results in the rotation of optical petal when both OAM modes pass through a polarizer. A photodetector is used to detect the intensity variation of the output from the polarizer followed by a slit. By using this method, we have experimentally achieved the superposition of OAM modes with the vector representation of HE ₂₁ mode for magnetic field sensing. And a magnetic field sensitivity of 3.31%/ $T$ can be reached at the width ratio of the slit to the petal-like pattern of 0.35 ± 0.02. The obtained experimental results prove the successful implementation of this proof-of-concept principle, showing its potential applications in all-fiber current sensing.