“The problem is that LEDs, although they are more energy efficient than incandescent light, they still can be improved in terms of their light output,” says Harald Haas, chair of mobile communications at the University of Edinburgh and a member of the Ultra-Parallel Visible Light Communications Project. “We strongly believe the next wave of energy efficient lighting will be based on laser diodes.” Li-Fi encrypts the data coming on the light from LEDs by adjusting their output. The rapid flickering is not visible to the human eye; however, a receiver on a desktop computer or mobile device can read the signal, and even send one back to a transceiver on the ceiling of a room resulting in a two-way communication. But several of the LEDs use a phosphor coating to convert blue light to white. This in turn limits the speed with which the devices can be adjusted, thereby holding down the data rates. A research published in Optics Express, Haas and his team exhibited that replacement of the LEDs with off-the-shelf laser diodes vastly improved the situation. Lasers, with their high energy and optical efficiency, can be adjusted at 10 times the rate of LEDs. On the other hand by using phosphors, laser lighting would create white light by mixing the output of several lasers operating at different wavelengths. This means that each wavelength can be used as a separate data channel, the same sort of wavelength division multiplexing that lets optical telecommunications carry so much data. The Edinburgh group’s experiment used nine laser diodes. While LED-based Li-Fi could reach data rates of 10 Gb/s, which is an improvement over the 7 Gb/s maximum of Wi-Fi; however, using lasers could enhance that speed to “easily beyond 100 Gb/s,” Haas says. Currently to go ahead with such a setup would be costly, but Haas believes that mass production will lower cost of the lasers and move them into lighting applications. BMW is already selling cars with laser-based headlights on its i8 model. “That is only the start of a technology move as laser diodes get more inexpensive,” Haas says.
