Visible light communication (VLC) is one of the key technologies for the sixth generation (6G) to support the connection and throughput of the Industrial Internet of Things (IIoT). Furthermore, VLC channel modeling is the foundation for designing efficient and robust VLC systems. In this paper, the ray-tracing simulation method is adopted to investigate the VLC channel in IIoT scenarios. The main contributions of this paper are divided into three aspects. Firstly, based on the simulated data, large-scale fading and multipath-related characteristics, including the channel impulse response (CIR), optical path loss (OPL), delay spread (DS), and angular spread (AS), are analyzed and modeled through the distance-dependent and statistical distribution models. The modeling results indicate that the channel characteristics under the single transmitter (TX) are proportional to the propagation distance. It is also found that the degree of time domain and spatial domain dispersion is higher than that in the typical rooms (conference room and corridor). Secondly, the density of surrounding objects and the effects of user heights on these channel characteristics are also investigated. Through the analysis, it can be observed that the denser objects can contribute to the smaller OPL and the larger RMS DS under the single TX case. Furthermore, due to the blocking effect of surrounding objects, the larger OPL and the smaller RMS DS can be observed at the receiver with a low height. Thirdly, due to the distance dependence of the channel characteristics and large time-domain dispersion, the link adaption method is further proposed to optimize the multipath interference problem. This method combines a luminary adaptive selection and delay adaption technique. Then, the performance of the link adaption method is verified from four aspects through simulation, including the signal-to-noise (SNR), the RMS DS, the CIRs, and the bit-error rate (BER) of a direct-current-biased optical orthogonal frequency division multiplexing (DCO-OFDM) system. The verification results indicate that our proposed method has a significant optimization for multipath interference.

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We present a method, based on the equivalent-current theory of optical waveguide coupling, by which metal-clad optical fiber polarizers can be analyzed. Good agreement between theoretical predictions and previously published experimental results is attained.

Terbium-doped optical fiber has high Verdet constant and is called magnetsensitive fiber. It is of importance for a variety of applications including magnetic field sensor, current sensor, and fiber-type isolator. In this paper, we describe magnet-sensitive optical fiber fabrication, magnetooptic coefficient measurement, and its application in current sensor system. Experimental results show that the Verdet constant of magnet-sensitive fiber containing high rare-earth content (-4000 parts in lOs) is 2.7 times as high as that of ordinary silica based fiber. When tested in current sensor system, it gives similar performance observed in ultralow birefringent fiber. These results are new and have not been published before.

A fiber-embeded optical isolator with in-line fiber polarizer is proposed and fabricated. The optical isolator consists of the in-line fiber polarizers , the crystal Faraday roator , and the fiber GRIN-rod coupling system. In the coupling system, the both conventional and polarization maintaining single-mode fiber have been utilized. Isolation and insertion losses at 1. 5pm are 25dB and 4. 5dB, respectively.