Meet the optical ‘couple’ that help speed and secure wireless communications – ScienceDaily


Han and Léia. Georges and Amal. Kermit and Miss Piggy. Gomez and Morticia. The greatest couples in history rely on communication to make them so strong that their power cannot be denied.

But that’s not only true of people (or Muppets), it’s also true of lasers.

According to new research from the USC Viterbi School of Engineering, recently published in Nature Photonics, adding two lasers together as a sort of optical “pair” promises to make wireless communications faster and more secure than ever. But first, a little reminder. Most laser communications – think fiber optics, commonly used for things like high-speed internet – are transmitted in the form of a laser (optical) beam passing through a cable. Optical communications are exceptionally fast but limited by the fact that they have to go through physical cables. Bringing the high-capacity capabilities of lasers to unattached and traveling applications – such as airplanes, drones, submarines, and satellites – is truly exciting and potentially revolutionary.

USC Viterbi researchers have brought us closer to this feat by focusing on something called Free Space Optical Communication (FSOC). This is no small feat, and it’s a challenge researchers have been working on for some time. A major obstacle has been what is called “atmospheric turbulence”.

When a single optical laser beam carrying information travels through the air, it experiences natural turbulence, much like an airplane. Wind and temperature changes in the surrounding atmosphere make the beam less stable. Our inability to control this turbulence is what has prevented the FSOC from achieving performance similar to that of radio and fiber systems. Leaving us stuck with older, slower radio waves for most wireless communications.

“Although the FSOC has been around for some time, it has been a fundamental challenge to effectively retrieve information from an optical beam that has been affected by atmospheric turbulence,” said Runzhou Zhang, senior author and PhD. . student at USC Viterbi Optical Communications Laboratory in Ming Hsieh Electrical and Computer Engineering Department.

The researchers moved forward in solving this problem by sending out a second laser beam (called a “pilot” beam) traveling with the first to act as a partner. Traveling as a couple, the two beams are sent in the same air, undergo the same turbulence and have the same distortion. If only one beam is sent, the receiver must calculate all the distortion experienced by the beam en route before it can decode the data. This considerably limits the performance of the system.

But, when the pilot beam moves along the original beam, the distortion is automatically removed. Like Kermit in the “Rainbow Connection” duo with Miss Piggy, the information in this bundle arrives at its destination in a clear, crisp, and easy-to-understand manner. From an engineering perspective, this achievement is no small feat. “The problem with radio waves, our current best bet for most wireless communications, is that they are much slower in terms of data throughput and much less secure than optical communications,” said Alan Willner, Chief team on paper and professor of electricity and electricity at USC Viterbi. engineering computer Science. “With our new approach, we get one step closer to mitigating turbulence in high capacity optical links.”

Perhaps most impressive, the researchers haven’t solved this problem with a new device or a new material. They just looked at physics and changed their perspective. “We used the underlying physics of a well-known device called a photodetector, typically used to detect the intensity of light, and realized that it could be used in a new way to advance problem solving. turbulence for laser communication systems, ”says Zhang.

Think of it this way: When Kermit and Miss Piggy sing their song, both of their voices are distorted in the air the same way. It makes sense; they stand next to each other and their sound travels in the same atmosphere. What this photodetector does is turn the distortion of Kermit’s voice into the opposite of the distortion of Miss Piggy’s voice. Now when they are mixed again, the distortion is automatically canceled in both voices and we hear the song clearly and precisely.

With this new application of physics, the team plans to continue exploring how to further improve performance. “We hope that our approach will one day lead to better and more secure wireless links,” said Willner. Such links can be used for everything from high resolution imaging to high performance computing.

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Material provided by University of Southern California. Original written by Ben Paul. Note: Content can be changed for style and length.

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