New research presents a low-energy means to overcome a fundamental barrier in free-space optical communication: The weather, in the form of clouds and rain. It particular, atmospheric clouds and fog form a formidable barrier to light propagation for free-space optical communication (FSO).
The main challenges is due to the randomness in size and position of water droplets leads to substantial scattering of the optical energy presented by atmospheric events.
FSO technology uses light propagating in free space to wirelessly transmit data for telecommunications or computer networking. The technology presents a significant advance on radio waves. However, there are obstacles, like those cause by the weather, and hence improvements can be made with the signal quality.
Rensselaer Polytechnic Institute’s Professor Moussa N’Gom and his team have devised a method to make communications between satellites and the ground more effective irrespective of the weather conditions.
In research recently published, the research team demonstrates how ultrafast, femtosecond lasers can be used to cut through the clouds and rain, avoiding the conditions that commonly cause losses in free-space optical communication (FSO).
According to N’Gom, the technology works thus: “The lasers we use are so energetic that they change the environment in which they propagate. The environment starts to change the laser that is changing it, and they have a light-matter interaction. It becomes a cascading effect that creates a long filament of light.”
In practice, the filament of light is accompanied by a shockwave, along the lines of a sonic boom. The laser filament proceeds to propagate through clouds. The accompanying shockwave clears the space around the filament, providing an open pathway for visible light. For this the researchers use structured light, in the form of a spiral with a hole at its centre, to propagate through the pathway.
Referred to as the Laguerre–Gauss beam, the light travels through this empty space without interacting with the filament and is unobstructed by the clouds. Under normal conditions, light travels in one, flat wave. With the new innovation, light travels in a spiral. This is sad to be much like curling a flat piece of paper with scissors.
This spiral shape of the light also allows for more information to be transmitted, at a rate substantially higher capacity than radio frequency communication.
The work was funded by the U.S. National Geospatial Agency.
The research appears in the Journal of Applied Physics, titled “Structured light signal transmission through clouds.”
