More stable way to send light through nano-photonic fibers

DAEJEON, South Korea, Sept. 19 (UPI) — Many phones, TVs and computers already rely on optical cables, which carry information in the form of light. But engineers have struggled to achieve stable light propagation across long distances. Thus, most optical cables require the introduction of an amplifier every so often.

New research promises an amplifier-free future for optical fibers.

In a new study, published this week in the journal Scientific Reports, researchers advocate abandoning the strategy most scientists have used to propagate a strong and stable optical pathway. The study authors call for scientists to abandon PT symmetry.

The “P” in PT symmetry stands for parity reversal and the “T” stands for time reversal. The concept refers to the interchangeability of concurrent light waves. Researchers liken the idea to a pair of cars on the highway. One is accelerating and the other decelerating, but for a brief moment, they’re both moving at the same speed — interchangeable. There is also time parity, because one can go back in time by switching from the accelerating car to the decelerating car.

Inside optical cables, the cars’ speed is the equivalent of the intensity of light. Time is the transfer of light between multiple cables. Light waves traveling down fibers in an optical cable overlap with one another. The phenomenon is known as tunneling.

As many scientists have found out the hard way, achieving PT symmetry by carefully controlling light intensity through optical cables is exceedingly difficult. It’s virtually impossible to make a pair of optical pathways exactly the same. No two fibers are alike.

Researchers at the Institute for Basic Science in Korea suggest abandoning PT symmetry and taking an alternative approach. Their latest research efforts suggest it is possible to maintain stable light propagation by deliberately making divergent optical pathways — the equivalent of choosing two different cars in the previous scenario.

“You have the potential to realize a lot of the items of the wish-list of the PT symmetry, by breaking the PT symmetry. But you have to break it in the right way,” Sergej Flach, director of the Center for Theoretical Physics of Complex Systems at IBS, said in an news release. “Now we know how to tune the characteristics of the fiber couplers to achieve a long-lasting constant light propagation.”


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