An optical fiber composite overhead ground wire (OPGW) distributed ice-coating monitoring scheme based on Brillouin optical time domain reflectometer (BOTDR) temperature measurement is proposed and demonstrated. The thermodynamic factors affecting the temperature of the OPGW cable are analyzed, and the temperature variation characteristics of the icing and non-icing sections of the OPGW cable with different icing thicknesses are analyzed via finite-element analysis. The results of an OPGW icing experiment indicate that when the ambient temperature changes, there is an obvious hysteresis characteristic between the temperature changes of the icing and non-icing sections of the OPGW cable, which is related to the thickness of the ice. Thus, we propose a distributed OPGW cable icing monitoring system based on BOTDR temperature monitoring.

A scheme for monitoring icing on overhead transmission lines with fiber Bragg grating (FBG) strain sensors is designed and evaluated both theoretically and experimentally. The influences of temperature and wind are considered. The results of field experiments using simulated ice loading on windless days indicate that the scheme is capable of monitoring the icing thickness within 0–30 mm with an accuracy of ±1 mm, a load cell error of 0.0308v, a repeatability error of 0.3328v and a hysteresis error is 0.026%. To improve the measurement during windy weather, a correction factor is added to the effective gravity acceleration, and the absolute FBG strain is replaced by its statistical average.

In this paper, we propose and demonstrate a low-complexity fiber nonlinearity impairments compensation (NLC) scheme based on simple recurrent neural network (SRNN), combining with the triplets derived from the first-order perturbation solution of the coupled nonlinear Schrodinger equation. Benefitting from the time memory of SRNN, the proposed NLC can reduce the computational complexity without sacrificing the compensation performance compared with the schemes based on memoryless feedforward neural networks. To verify the feasibility of the proposed NLC, the simulation systems of single channel and three channel 30 GBaud polarization division multiplexing (PDM) 16 quadrature amplitude modulation (QAM) over 2400 km standard single mode fiber transmission are constructed respectively. Comprehensive numerical simulation results demonstrate that although the NLC performance of proposed scheme is inferior to that of digital back propagation (DBP) with much higher complexity and impracticality, it can still achieve the competitive NLC performance with lower computational complexity compared to the schemes based on deep neural network (DNN) and artificial neural network (ANN). Moreover, it is further proved that using triplets as the feature required for NLC can cause the pattern of pseudo random bit sequence to be destroyed, resulting in the neural network-based NLC scheme not suffering from the problem of overestimation for performance. Additionally, the time memory of SRNN enables the number of triplets in training set required by the SRNN-based NLC to be reduced by 169% compared to that of DNN and ANN. The experimental results of 16 GBaud PDM-16QAM wavelength division multiplexing coherent systems demonstrate that compared to with ANN and DNN, the comparable NLC performance can also be achieved by the proposed scheme with lower complexity.

We investigate the communication performance of a few-mode EDFA based all-optical relaying system for atmospheric channels in this paper. A dual-hop free space optical communication model based on the relay with two-mode EDFA is derived. The BER performance is numerically calculated. Compared with all-optical relaying system with single-mode EDFA, the power budget is increased by 4 dB, 7.5 dB and 11.5 dB at BER $= 1\times10^{-4}$ under the refractive index structure constant $C^2_n = 2\times10^{-14}, 5\times10^{-14}$ and $1\times10^{-13}$ respectively when a few mode fiber supporting 4 modes is utilized as the receiving fiber at the destination. The optimal relay location is slightly backward from the middle of the link. The BER performance is the best when mode-dependent gain of FM-EDFA is zero.

The sharply growing demand for increased transmission capacity and bandwidth in last meter and last mile access networks together with the commercialization of fifth generation (5G) wireless systems has been opening up new opportunities for non-radio frequency (RF)-based wireless technologies. Visible light communications (VLC) technology is a potential candidate for access networking in 5G, which offers a higher spectral efficiency than RF-based Femtocell networks by three orders of magnitude. This paper proposes an all wireless optical bidirectional VLC multiple access scheme for pure VLC network access points in terminals. Centralized coordination is adopted to reduce the system complexity. And reservation of resource is introduced to guarantee collision avoidance during data frame transmission. The proposed multiple access scheme introduces special system parameters to achieve the balance of system throughput and access latency. The feasibility of the proposed scheme is verified by both theoretical analysis and experimental investigation. We show that the proposed scheme is suitable for a bidirectional pure VLC access network and can be used as a supplement in the IEEE 802.11 bb for 5G+bidirectional VLC application scenarios.

A novel insulator string leakage current-monitoring sensor based on a fiber Bragg grating (FBG), cantilever beam, and spiral coil is demonstrated. The spiral coil is used to convert the leakage current into the force exerted on the cantilever structure, which is obtained by measuring the strain of the FBG. Experimental results show that the linear regression correlation coefficient is 0.99964. In addition, although the leakage current measurement is not sufficiently accurate, the 50-Hz component measurement is accurate. The sensor is suitable for use as an insulator string flashover warning and has promising prospects for future grid security protection applications.