Solid-state lighting is a rapidly growing area of research and applications, due to the reliability and predicted high efficiency of these devices. The white LED sources that are typically used for ...general illumination can also be used for data transmission, and Visible Light Communications (VLC) is a rapidly growing area of research. One of the key challenges is the limited modulation bandwidth of sources, typically several MHz. However, as a room or coverage space would typically be illuminated by an array of LEDs there is the potential for parallel data transmission, and using optical MIMO techniques is potentially attractive for achieving high data rates. In this paper we investigate non-imaging and imaging MIMO approaches: a non-imaging optical MIMO system does not perform properly at all receiver positions due to symmetry, but an imaging based system can operate under all foreseeable circumstances. Simulations show such systems can operate at several hundred Mbit/s, and up to Gbit/s in many circumstances.
Previously, when selecting silicon photomultipliers (SiPMs) for use in visible light communications (VLC) systems the bandwidth of the SiPM has been a high priority. However, results of experiments ...on VLC receivers containing two different sizes of commercially available SiPMs show that, if equalization is used and the OOK bit time is less than one third of the duration of its output pulses, the SiPMs bandwidth doesn't significantly impact the receiver's performance. Consequently, for these data rates the criteria used to select which SiPM to incorporate in VLC receivers should put a higher priority on their area and photon detection efficiency than on their bandwidth. In addition, for these data rates, unless the SiPM becomes non-linear, the performance of a receiver containing a SiPM can be predicted based upon Poisson statistics.
Visible light communications (VLC) has the potential to play a major part in future smart home and next generation communication networks. There is significant ongoing work to increase the achievable ...data rates using VLC, to standardize it and integrate it within existing network infrastructures. The future of VLC systems depends on the ability to fabricate low cost transceiver components and to realize the promise of high data rates. This paper reports the design and fabrication of integrated transmitter and receiver components. The transmitter uses a two dimensional individually addressable array of micro light emitting diodes (μLEDs) and the receiver uses an integrated photodiode array fabricated in a CMOS technology. A preliminary result of a MIMO system implementation operating at a data rate of 1 Gbps is demonstrated. This paper also highlights the challenges in achieving highly parallel data communication along with the possible bottlenecks in integrated approaches.
This letter presents a novel technique to achieve high-speed visible light communication (VLC) using white light generated by a blue GaN μLED and a yellow fluorescent copolymer. We generated white ...light suitable for room illumination by optimizing the ratio between the blue electroluminescence of the μLED and yellow photoluminescence of the copolymer color converter. Taking advantage of the components' high bandwidth, we demonstrated 1.68 Gb/s at a distance of 3 cm (at 240 lx illumination). To the best of our knowledge, this is the fastest white light VLC results using a single blue LED/color converter combination.
White light-emitting diodes (LEDs) are becoming widespread in commercial lighting applications, and there are predictions that they will be in common use in domestic applications in the future. There ...is also growing interest in using these devices for both illumination and communications. One of the major challenges in visible light communications is the low modulation bandwidth (BW) available from devices, which is typically several megahertz. In this letter, we describe a link that uses 16 LEDs which are modulated using a resonant driving technique, creating an overall BW of 25 MHz. This is used to implement a 40-Mb/s nonreturn-to-zero on-off keying link which operates at low error rates, and also provides illumination at levels sufficient for a standard office environment.
In this paper, we report the performance of an imaging multiple-input multiple-output (MIMO) visible light communication (VLC) system. The VLC transmitter consists of a two-dimensional (2-D), ...individually addressable Gallium Nitride micro light-emitting diode (μLED) array. The receiver uses a 2-D avalanche photodiode array fabricated using complementary metal oxide semiconductor (CMOS). Using integrated CMOS-based LED drivers, a data rate greater than 1 Gb/s was obtained at a link distance of 1 m with the system field of view of 3.45° using four channels. At a reduced link distance of 0.5 m, a data rate of 7.48 Gb/s was obtained using a nine channel MIMO system. This demonstrates the feasibility of compact MIMO systems that offer substantial data rates.
Lasers possess many attractive features (e.g., high brightness, narrow linewidth, well-defined polarization) that make them the ideal illumination source for many different scientific and ...technological endeavors relating to imaging and the display of high-resolution information. However, their high-level of coherence can result in the formation of noise, referred to as speckle, that can corrupt and degrade images. Here, we demonstrate a new electro-optic technology for combatting laser speckle using a chiral nematic liquid crystal (LC) dispersed with zwitterionic dopants. Results are presented that demonstrate when driven at the optimum electric field conditions, the speckle noise can be reduced by >90% resulting in speckle contrast (C) values of C = 0.07, which is approaching that required to be imperceptible to the human eye. This LC technology is then showcased in an array of different display and imaging applications, including a demonstration of speckle reduction in modern vectorial laser-based imaging.
In this paper, the performance of a wide field of view VLC receiver that includes a silicon photomultiplier (SiPM) is reported. In particular, a receiver field of view of ±45° and On-Off keying data ...rates of 1.8 Gbps are demonstrated in 500 lux of ambient light. These results are achieved by combining optical absorption filters with a 6 mm by 6 mm SiPM. By absorbing ambient light between 450 nm and 750 nm these filters ensure that the SiPM is not saturated and reduces the transmitter power needed to support the required data rate. Unlike other optical filters the performance of absorption filters is not sensitive to angle of incidence. Consequently, the FOV is explained by a combination of the changes to the receiver's projected area, the path length of light in the filters and reflections from the filter surfaces. In addition, the results of the calculations, described by the IEC 62471:2006 safety standard, needed to determine the eye safety of a transmitter are reported. These calculations and the resulting irradiance levels available in a representative office scenario are used to show that data rates of more than 1 Gbps could be achieved with eye safe transmitters.
Fiber-wireless-Fiber links require alignment between the transmitter and receiver to a high degree of precision (typically ~ 0.01° for a link of a few meters), and channel coding can be used for ...mitigating the link margin reduction caused by the limited precision of the beam-steering and tracking system. This paper reports results from an experimental study of the misalignment tolerance attained by channel coding. Explicitly, the received power penalties imposed by misalignment are characterized, and then forward error correction techniques are adopted for mitigating the performance degradation inflicted, which is quantified experimentally. Our results characterize trade-offs between coding rate, decoding complexity and the degree of misalignment. Overall, an improvement of the tolerance to misalignment up to ~50% was attained for coded links compared with the uncoded counterpart.
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