Although patterns of light show great promise for a vast encoding alphabet in optical communications, development is hampered by these patterns’ sensitivity to distortion, such as that caused by air turbulence or bent optical fiber.
Researchers at the University of the Witwatersrand (Wits) have now proposed a new optical communication protocol that uses spatial patterns of light for multi-dimensional encoding without requiring recognition of the patterns, thus getting around the earlier restriction of modal distortion in noisy channels.
As a result, a novel state-of-the-art encoding of over 50 vectorial patterns of light conveyed almost noise-free over a turbulent environment has been developed, paving the way for a new approach to high-bit-rate optical communication.
The Wits researchers from the Structured Light Laboratory at the Wits School of Physics employed a new invariant characteristic of vectorial light to encode information in a study published this week in Laser & Photonics Reviews.
This parameter, dubbed “vectorness” by the researchers, scales from 0 to 1 and remains constant when going through a noisy channel.
The researchers exploited the invariance to split the 0 to 1 vectorness range into more than 50 parts (0, 0.02, 0.04, and so on up to 1) for a 50-letter alphabet, as opposed to classical amplitude modulation, which is simply 0 or 1 (only a two-letter alphabet).
Since the channel via which the information is transmitted does not alter the vectorness, both the sender and the receiver will always agree on the value, resulting in noise-free information transfer.
The researchers overcome a crucial barrier by using light patterns in a way that does not need them to be “recognized,” allowing the inherent distortion of noisy channels to be ignored. Instead, the invariant amount simply “adds up” light in specialized measurements, showing a quantity that is not affected by the distortion.
This is a very exciting advance because we can finally exploit the many patterns of light as an encoding alphabet without worrying 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 not at all influenced by the noise of the channel.
Andrew Forbes, Professor, School of Physics, University of the Witwatersrand
Study lead author and Ph.D. candidate Keshaan Singh added, “To create and detect the vectorness modulation requires nothing more than conventional communications technology, allowing our modal (pattern) based protocol to be deployed immediately in real-world settings.”
The team has already begun experiments in optical fiber and rapid networks over free space, and they hope the concept will work in additional noisy channels, including underwater.