Fog has a strong attenuation effect on the optical channel, which will greatly degrade the performance of visible light communication (VLC). Studying the effect of the fog on communication performance is crucial to realize outdoor VLC for next generation networks, but there is little research on this topic. In this work, the transmission characteristics of visible light band in the foggy channel were measured and a high-speed VLC system based on a 450 nm blue laser diode (LD) and 16-ary quadrature amplitude modulation orthogonal frequency division multiplexing (16-QAM-OFDM) in the artificial fog environment was demonstrated experimentally. Through a foggy channel of 60 cm, a maximum data rate of up to 4 Gbps was achieved at the pass loss of 13.06 dB with a bit error rate (BER) of 3.5 × 10−3 below the forward error correction (FEC) limit (3.8 × 10−3), which was the highest data rate ever reported for VLC in the foggy channel. Even at a higher pass loss of 17.32 dB, the proposed system still could achieve a data rate of 2.84 Gbps with a BER of 2.8 × 10−3. Further extending the distance to 16.9 m for a more practical application, a data rate of 2.0 Gbps was also demonstrated successfully.

The present study reports a simple quenching method to simultaneously improve flux pinning and grain connectivity in polycrystalline H-doped MgB2, which was ex-situ synthesized at 350 oC under the H2 pressure of 3 MPa. Quenching prevented the phase transformation of β-Mg(BH4)2→α-Mg(BH4)2 upon cooling, and the dominant point-pinning effects originated from the self-generated nano-sized β-Mg(BH4)2 particles that were confined within the MgB2 grains. A semi-coherent relationship was found between MgB2(100) and Mg(BH4)2(—11—4) planes. Meanwhile, the precipitation-induced expansion of the MgB2 grains remained at room temperature, leading to an increasing number of contact points as well as grain connectivity. Compared with the un-doped MgB2, the quenched H-doped one exhibited enhanced critical current density over the entire field. These results are expected to guide the design of flux pinning centers for improving the Jc performance of standard type II superconductors.

Traffic signs should provide clear signals for drivers and passengers under various environmental and geographic conditions. In foggy weather, the signal will be disturbed due to light scattering, which will cause obstacles to recognition. This study simulated a foggy environment in the laboratory, used a standard color card as the target, and introduced a colorimeter to record the color coordinates, then calculated the color difference and analyzed the four-color samples’ color properties in different lighting conditions. We found that as the relative visibility increases, the chromatic aberration of the sample will gradually decrease under different lighting conditions and reach zero when the relative visibility is higher than 70%. We found that the green and blue samples have better color coordinate retention capabilities than the fog’s red and yellow. We compared all tested light sources’ performance, and the results showed that 3000K LED and incandescent lamps are better than other light sources. This study will provide a data basis for the study of traffic safety and accident prevention.

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