Researchers demonstrate noise-free communication with structured light

Light patterns hold great promise for large coding alphabets in optical communications, but progress is hampered by their susceptibility to distortion, such as atmospheric turbulence or bent optical fiber.

Now, researchers at the University of the Witwatersrand (Wits) have established a new optical communication protocol that uses spatial patterns of light for multidimensional coding without the need for pattern recognition, thereby overcoming the prior limitation of modal distortion. in noisy channels. The result is a novel encoding of more than 50 vector patterns of light transmitted virtually noiselessly through a turbulent atmosphere, opening up a new approach to high-resolution optical communications.

published in Laser and Photonics Reviews, the Wits team from the Structured Light Laboratory in the Wits School of Physics used a new invariant property of vector light to encode information. This quantity, which the team calls a “vector,” scales from 0 to 1 and remains unchanged when passed through a noisy channel.

Unlike traditional amplitude modulation, which is either 0 or 1 (just a two-letter alphabet), the command divides the vector range from 0 to 1 into more than 50 divisions (0, 0.02, 0.04, etc. to 1). used an invariant to divide. An alphabet of 50 letters. Since the channel through which information is transmitted does not violate vectority, both sender and receiver always agree on the value, hence noise-free information transfer.

A key hurdle the team overcame was using light patterns in a way that didn’t require “recognition” of noisy channels, to ignore the natural distortions of noisy channels. Instead, an invariant quantity “turns on” the light in specialized measurements, indicating a quantity that sees no distortion at all.

Professor Andrew Forbes of the Wits School of Physics says: “This is a very exciting achievement because we can use many patterns of light as a coding alphabet without having to worry about how noisy the channel is.” “In fact, the only limit to how big the alphabet can be is how good the detectors are, and the channel noise is completely unaffected.”

Lead author and Ph.D. candidate Keshaan Singh adds, “The generation and detection of vector modulation requires nothing more than conventional communications technology, allowing us to immediately deploy our modal (pattern)-based protocol in real-world settings.”

The team has already begun demonstrations on optical fiber and fast communication in free space, and believes the approach could work in other noisy channels, including underwater.