Fiber-optic cables allow data to travel around the world at the speed of light. But according to SSLEEC collaborator John Bowers, professor in the Department of Electrical and Computer Engineering and director of the UCSB Institute for Energy Efficiency, “As we move from a tethered existence, in which computers are tied to the wall with Ethernet cable, to an untethered, wireless existence, another chapter is emerging in the story of light and data transmission.”
That chapter is being written by light fidelity, or Li-Fi, which enables wireless communications to be transmitted at unprecedented speeds.”
Li-Fi’s familiar predecessor, Wi-Fi, has advanced tremendously since a rudimentary form of it was introduced in 1991, and the 5G network, expected to roll out in 2020, will be a significant next step in terms of both bandwidth and download speed. But Wi-Fi has limits, says Bowers, a world expert in the field of light-based data transmission.
Because light waves have a much higher frequency than the electromagnetic waves used by Wi-Fi, they transmit faster and can carry much more information. A standard household LED lightbulb in a Li-Fi system could transfer data at a up to 100 megabits per second (Mbps). Laser-based Li-Fi would be even faster, with speeds up to 100 gigabits (Gbps) per second compared to the quite-fast, but comparatively snail-like, 5G network, which is expected to boost streaming speeds from 4G’s current 1 or 2 Gbps to 10 Gbps.
The fiber-optic backbone does that today. “The issue,” Bowers explains, “is getting that high capacity out of the fiber and into the wireless space between the end of the fiber and your laptop, cellphone, or other device. That’s the bottleneck.”
Bowers explains that the computer connector to a device used to transmit data at 1 Gbps. Now it’s up to 10 Gbps. Newer versions of those connectors will be running at 50 and 100 Gbps. He adds, “The antenna in electronic devices does not have that capacity, but because transmission is typically asymmetric, we can use Lif-Fi to transmit to our electronic devices at 100 Gbps or higher, and the return path could be wireless. Because light wavelengths are so short — a fraction of a micron — the photodetector could be small. Right now the entire outside of a cell phone is the antenna. A visible-light detector able to run 100 Gbps is small and cheap, so the phone could be thinner, more data-intensive, and less expensive.”
In his SSLEEC research, Bowers has worked to increase the speed of indium gallium nitride (InGaN) lasers so that they can transmit data at higher rates. “It is clear now that eventually, every room will have a laser or LED light source; they’re ubiquitous and inexpensive,” he says. “What’s not as clear is whether the cost will allow for putting data on top of that.”
In the late 1990s, Bowers worked on the first “mode locking” of an InGaN laser. Mode locking (versus direct modulation) is a way of generating extremely short optical pulses, which enables the laser to transmit data at even higher rates, up to hundreds of Gbps when used in concert with integrated external modulators.
According to Bowers, “We demonstrated mode locking fifteen years ago, primarily to investigate the science and physics of transition times in GaN lasers. At that point, Li-Fi wasn’t yet an issue. Wi-Fi had plenty of data capacity for anyone’s needs, so there wasn’t’ a reason to focus on it. But that has changed.”
Today, he and SSLEEC director, Steve DenBaars, continue their efforts on laser modulation, so that they can directly modulate the laser at gigabit speeds, and then use external modulation to move to higher data rates. According to Bowers, “We have the experience and tools from telecommunications and data communications, and we can apply them to Li-Fi.”