Facebook says it has developed a laser detector that could open the airwaves to new high-speed data communications systems that don’t require dedicated spectrum or licenses. The component, disclosed on recently in a scientific journal, comes from the company’s Connectivity Lab, which is involved in developing technology that can help spread high-speed Internet to places it currently doesn’t reach.
Getting Internet signals to new areas is typically done using wireless, because it’s much more cost-efficient than running cables to communities outside of urban areas. But traditional wireless comes with speed limitations and requires radio spectrum that often needs to be purchased from the government. Faced with these limitations, engineers have increasingly eyed sending data from point-to-point over laser beams. They don’t need any special spectrum or permission, and multiple systems can work in the same area without interfering with each other.
But sending high speed signals using lasers isn’t simple. First, to achieve multi-gigabit per second speeds, the photodiodes used to receive the signal need to work very fast. And that means they need to be small—just a millimeter square, or several times smaller than a grain of rice. And laser beams spread out as they travel, so by the time they reach their destination they can cover an area much bigger than the detector itself and need to be focused using lenses. This reduces the aperture of the system, so a complex pointing and aiming system is required to keep the laser locked onto the receiver.
In short, it’s an engineering feat to get it working even at low speeds. Getting it to work at higher speeds it a real challenge. Now Facebook thinks it’s found a way, by developing a new detector that’s much larger but can still operate at high speeds.
At 126 square centimeters, Facebook’s new laser detector is thousands of times larger. It consists of plastic optical fibers that have been “doped” so they absorb blue light. The fibers create a large flat area that serves as the detector. They luminesce, so the blue light is reemitted as green light as it travels down the fibers, which are then bundled together tightly before they meet with a photodiode.