Facebook’s Lightbulb: Facebook’s Connectivity Lab has designed a lightbulb-shaped detector that can receive information-carrying beams of light from any angle. Rather than the costly process of building towers and burying cables, Facebook is taking the internet to the sky to get those people online, much like Google’s Project Loon. After last year unveiling the drones that would beam data-laden lasers down to remote areas, the social netowrking giant’s Connectivity Lab has now solved the problem of how those beams of light are received on the ground, achieving speeds of up to 2 Gbps. Transmitting information wirelessly using light, or free-space optical communication, has the potential for very high bandwidths and data capacity. The problem is, it’s a precise science at the best of times, and aiming a tiny laser at a tiny photodetector across vast distances is no easy task, especially when the laser is moving. Using mechanical systems to reorient the detector so the laser hits it is one solution, but it’s not an elegant one.
Connectivity Lab team designed a lightbulb-shaped light collector, made up of a bundle of fluorescent, plastic optical fibers. With a surface area of 126 sq cm (19.5 sq in), the unique shape of the device allows it to collect light from any angle, which it then concentrates onto a small photodetector. The fibers also contain organic dye molecules that absorb blue light but emit green. The high speeds in question can reach up to 2 Gbps, which is even more impressive when you consider that the system only has a bandwidth of 100 MHz. The speeds are thanks to the use of orthogonal frequency division multiplexing (OFDM), which is a method of encoding data that allows multiple streams to be transmitted simultaneously. The fact that it takes less than two nanoseconds for the device to absorb blue light and emit green light helps as well. The researchers say blistering speeds of up to 10 Gbps may be possible in future, if the system can be adapted to incorporate materials that work with infrared wavelengths.