SPIE Newsroom, 19 April 2013
White LEDs hold promise as a key enabler for future wireless networks based on optical attocells, offering significant improvements to indoor data coverage.
The advent of the first cellphones in the 1980s marked the beginning of commercial mobile communications. Now, only 30 years later, wireless connectivity has become a fundamental part of our everyday lives and is increasingly being regarded as an essential commodity like electricity, gas, and water. The technology's huge success means we are now facing an imminent shortage of radiofrequency (RF) spectrum. The amount of data sent through wireless networks is expected to increase 10-fold during the next four years.1 At the same time, there isn't enough new RF spectrum available to allocate. In addition, the spectral efficiency (the number of bits successfully transmitted per Hertz bandwidth) of wireless networks has become saturated, despite tremendous technological advancements in the last 10 years. The US Federal Communications Commission has therefore warned of a potential spectrum crisis.
Light fidelity (Li-Fi),2 the high-speed communication and networking variant of visible light communication (VLC),3 aims to unlock a vast amount of unused electromagnetic spectrum in the visible light region (see Figure 1). Li-Fi works as a signal transmitter with the off-the-shelf white LEDs typically used for solid-state lighting and as a signal receiver with a p-i-n photodiode or avalanche photodiode. This means that Li-Fi systems can illuminate a room and at the same time provide wireless data connectivity. Unlike laser diodes, the LEDs my colleagues and I studied produce incoherent light, which means the signal phase cannot be used for data communications. Therefore, the only way to encode data is to use intensity modulation and direct detection. This poses severe restrictions on the data rates we can achieve.