Coverage Improvement of Laser Diode-Based Visible Light Communication Systems Using an Engineered Diffuser

A combination of a blue laser diode (LD) and a warm white light emitting diode (LED) has been used for indoor lighting and visible light communications (VLC). Contrary to LD and phosphor based white lighting communication, no blue LD power is lost due to phosphor conversion. As a result, a longer communication distance has been achieved. The laser beam is diffused in a hat-top profile by an engineered diffuser in such a way that the received signal strength remains flat over a large area, thus improving the coverage area of the communication system. The experiment demonstrates a 1.7 Gbits/s communication speed over a distance of 1.85 m keeping bit error rate (BER) below $2.8\times 10^{-3}$ over a large area. The coverage area has been improved by 238 % to $2.27 m^{2}$ using the hat-top diffuser from $0.95 m^{2}$ for a phosphor diffuser. This is the largest reported coverage area for the achieved VLC speed at a 1.85 m distance to the best of the authors’ knowledge. A correlated color temperature (CCT) of 2952 and a color rendering index (CRI) of 86 have been achieved and the blue light exposure has been kept under the permitted limit. As the radiation standards for eye safety are more relaxed for the infrared (IR) spectrum compared to the visible spectrum, a near-IR LD has been utilized to achieve higher data rates. A data rate of 2.55 Gbits/s has been achieved using the near-IR LD and the proposed diffuser for the same coverage area and distance.