Recently, Facebook’s Connectivity Lab team published a paper in the journal “Optica†on the use of fluorescence-boosting signal detection in free-space optical communications. Free-space optical communication is undoubtedly related to Project Aquila launched by Facebook last year. The project aims to use a solar unmanned aerial vehicle and a signal station to form a network and transmit data to the ground through laser communications. You don't need to lay fiber-optic cables to connect remote areas to the Internet.
The co-authors of this paper include T. Peyronel, KJ Quirk, SC Wang, and TG Tiecke, all of whom are Facebook employees. The paper shows that the use of fluorescent materials can increase the effective area and field of view of the photodiode without sacrificing the reaction time. The specific method is to select a certain density of dye covering the surface of the detector to make it a Luminescent detector (LD). Because of the effect of the fluorescent dye, the detector can absorb light of a certain wavelength and then use it again. The wavelengths of light are emitted. For example, it absorbs blue light but emits green light.
This conversion of light wavelengths is very rapid. For example, it takes less than 2 nanoseconds to absorb light from blue light to green light emission. In addition, a technique called "orthogonal frequency division multiplexing" (OFDM) is used in spite of the broadband of the system. It is 100MHz and the transmission rate can also exceed 2 Gbps. Researcher TG Tiecke said that this new technology will theoretically exceed the 10 Gbps optical transmission rate of free space.
The shaped fluorescence detector shows a bulb shape as shown in the figure below. It consists of a single piece of fluorescent sheet module that absorbs light in all directions.
Picture from: Facebook Connectivity Lab
Fluorescence detectors have proven to increase their effective area by 3 orders of magnitude, while also demonstrating a full range of sensitivities. The paper states that future research will focus on the development of custom materials for communications applications.
One of the problems that currently exists with the Laserbird UAV is that it generates sparks when it travels through the network. It is also called "flash." The turbulence in the atmosphere can cause light to fluctuate, eventually causing the signal to weaken. The researchers believe that this new technology with dyes will likely suppress this spark effect.
Despite the broad prospects of this study, it is not enough to allow the Tian Ying laser drone to complete its goal of covering remote areas, because there is another big problem that plagues drones: batteries. And this new optical technology will still need more experiments in reality.
Via OSA Publishing, TC