![]() ![]() In the modern era, semaphores and wireless solar telegraphs called heliographs were developed, using coded signals to communicate with their recipients. The ancient Greeks used a coded alphabetic system of signalling with torches developed by Cleoxenus, Democleitus and Polybius. Optical communications, in various forms, have been used for thousands of years. History A photophone receiver and headset, one half of Bell and Tainter's optical telecommunication system of 1880 The technology is useful where the physical connections are impractical due to high costs or other considerations. This contrasts with using solids such as optical fiber cable. "Free space" means air, outer space, vacuum, or something similar. At the top right corner is a monocular for assisting the alignment of the two heads.įree-space optical communication ( FSO) is an optical communication technology that uses light propagating in free space to wirelessly transmit data for telecommunications or computer networking. The receptor is the large lens in the middle, the transmitters the smaller ones. For short- to medium-range communication, see Optical wireless communications.Īn 8-beam free-space optics laser link, rated for 1 Gbit/s. The research is published in the Journal of Applied Physics.This article is about optical communication over long distances. "I expect free-space optical communication technology of this type to enable hyper-speed secure worldwide quantum communications." N'Gom's innovative research shows how to overcome a fundamental barrier in free-space optical communication," said Curt Breneman, dean of the Rensselaer School of Science. Previous attempts to overcome the persistent obstacle of rain and clouds required substantial energy, large investments, or were less effective. ![]() The method presents a significant advance for FSO, which already has substantially higher capacity than radio frequency communication. On top of facilitating transmission through clouds, the spiral shape of the light also allows for more information to be transmitted. ![]() Imagine it like curling a flat piece of paper with scissors." "Normally, light travels in one, flat wave, but the light we create travels in a spiral. "The Laguerre–Gauss beam travels through this empty space without interacting with the filament and is unobstructed by the clouds," N'Gom said. N'Gom uses structured light, in the form of a spiral with a hole at its center, to propagate through the pathway. The laser filament propagates through clouds and the accompanying shockwave clears the space around the filament, providing an open pathway for visible light. The filament of light is accompanied by a shockwave, along the lines of a sonic boom. It becomes a cascading effect that creates a long filament of light." "The environment starts to change the laser that is changing it, and they have a light-matter interaction. "The lasers we use are so energetic that they change the environment in which they propagate," N'Gom said. In research recently published, N'Gom and his team used ultrafast, femtosecond lasers to cut through the clouds and rain that commonly cause losses in free-space optical communication (FSO). Rensselaer Polytechnic Institute's Moussa N'Gom, assistant professor of physics, applied physics, and astronomy, has devised a method to make communications between satellites and the ground more effective no matter the weather. Credit: Journal of Applied Physics (2023). (c) Filament propagates through the chamber containing a sparse cloud. (b) Side view picture of the filament (glowing line) in the air with a yellow line as a guide. After filtering out the femtosecond pulse with DM, IF, and ND, the structured light is imaged by an sCMOS camera. The structured light beam generated by the SLM is coupled with the filament by the MC before entering the cloud chamber. L, lens ?=2-m BE, beam expander SLM, spatial light modulator I, Iris DM, dichroic mirror IF, interference filters ND, neutral density filters and MC, mirror coupler. ![]()
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