In general, visible light communication (VLC) systems, which utilise white light-emitting diodes (LEDs), only offer a bandwidth limited to the low MHz region. Therefore, providing VLC-based high data rate communications systems becomes a challenging task. To address this challenge, we propose a solution based on multiplexing in both the frequency and space domains. We experimentally demonstrate a 4 $\times$ 4 imaging multiple-input multiple-output (MIMO) VLC system (i.e., space multiplexing) utilising multi-band carrier-less amplitude and phase (m-CAP) modulation (i.e., frequency multiplexing). Independently, both MIMO and m-CAP have shown the remarkable ability to improve transmission speeds in VLC systems, and hence, here we combine them to further improve the net data rate. We investigate link performance by varying the number of subcarriers m, link distance L, and signal bandwidth B$_{sig}$. From all the values tested, we show a data rate of ~249 Mb/s can be maximally achieved for m = 20, B$_{sig}$ = 20 MHz, and L = 1 m, at a bit error rate of 3.2$\times$10$_{-3}$ using LEDs with ~4 MHz bandwidth.

In optical camera communication (OCC) systems leverage on the use of commercial off-the-shelf image sensors to perceive the spatial and temporal variation of light intensity to enable data transmission. However, the transmission data rate is mainly limited by the exposure time and the frame rate of the camera. In addition, the camera's sampling will introduce intersymbol interference (ISI), which will degrade the system performance. In this paper, an artificial neural network (ANN)-based equaliser with the adaptive algorithm is employed for the first time in the field of OCC to mitigate ISI and therefore increase the data rate. Unlike other communication systems, training of the ANN network in OCC is done only once in a lifetime for a range of different exposure time and the network can be stored with a look-up table. The proposed system is theoretically investigated and experimentally evaluated. The results record the highest bit rate for OCC using a single LED source and the Manchester line code (MLC) non-return to zero (NRZ) encoded signal. It also demonstrates 2 to 9 times improved bandwidth depending on the exposure times where the system's bit error rate is below the forward error correction limit.

Today’s lowest-loss hollow core fibers are based on antiresonance guidance. They have been shown both theoretically and experimentally to have very low levels of backscattering arising from the fiber structure – 45 dB below that of traditional optical fibers with a solid silica glass core. This makes their longitudinal characterization using conventional reflectometric techniques very challenging. However, it was recently estimated that when filled with air, their backscattering coefficient increases to about 30 dB below that of standard solid core fibers. This level should be measurable with commercially available high performance optical time domain reflectometers (OTDR). Here we demonstrate – for the first time to the best of our knowledge – the measurement of backscattering from the air inside a hollow core fiber. We show that the characterization of multi-km long hollow core fibers with 15 m spatial resolution is possible using a commercial OTDR instrument. To benefit from its full dynamic range, we strongly suppress the 4% back-reflections that ordinarily occur at the OTDR’s standard fiber output when directly-connected to a hollow core fiber. Furthermore, low coupling loss into the hollow core fiber (0.3 dB in our experiment) also helps to maximize the achievable OTDR signal-to-noise ratio. This approach enables distributed characterization and fault-finding in low-loss hollow core fibers, a topic of increasing importance as these fibers are now starting to be installed in commercial optical communication networks.

In this letter, we investigate the performance of vehicular visible light communications based on the radiation patterns of different commercial taillights (TLs) using non-sequential ray tracing simulations. Our simulation results indicate a significant variation in the path loss compared with Lambertian model. Based on the ray tracing results, we propose a new path loss model as a function of the propagation distance considering the asymmetrical radiation pattern of TLs. We use this model to derive the attainable transmission distance. We further present the delay spread for various vehicular communication scenarios to demonstrate the effect of neighboring vehicles.

We propose an approach to interconnect a hollow-core fiber (HCF) of arbitrary core size with standard single-mode fiber with perfect mode-field size adaptation and experimentally achieve for the first time insertion loss agreeing with that predicted by simulations. We demonstrate this using three low-loss HCFs, including 1st window nested antiresonant nodeless fiber (NANF), 2nd window NANF and the state-of-the-art double NANF (DNANF). The connection with a minimum achieved insertion loss of 0.079 dB was permanently secured via gluing and did not degrade during 4 weeks of continuous measurement. To the best of our knowledge, this is the lowest reported value and is comparable to or lower than the connection between dissimilar single-mode fibers (e.g., standard single-mode fiber and dispersion-compensating fiber). We also show that such connection leads to excellent suppression of higher-order modes coupling, of importance to all applications sensitive to multi-path interference. Importantly, obtaining agreement between simulations and experiments validates for the first time the accuracy of the simulations and opens the door to further optimization via simulations with the ability to subsequently achieve the same result experimentally.