Twisted Light Carries More Data

Broadband fiber-optics carry information on pulses of light through optical fibers. But the way the light is encoded at one end and processed at the other affects data speeds. This world-first nano­photonic device encodes more data and processes it much faster than conven­tional fiber optics by using a special form of twisted light.

An ultrathin OAM-dispersive plasmonic topological insulator film is constituted by spatially shifted semi-circular nanogrooves and mode-sorting nanoapertures, through which the OAM-superposed beams are spatially separated and directly measured by a CMOS detector in the far-field region. (Source: RMIT)

Haoran Ren from RMIT’s School of Science said the tiny nano­photonic device they have built for reading twisted light is the missing key required to unlock super-fast, ultra-broadband communi­cations. “Present-day optical communi­cations are heading towards a capacity crunch as they fail to keep up with the ever-increasing demands of Big Data,” Ren said. “What we’ve managed to do is accu­rately transmit data via light at its highest capacity in a way that will allow us to massively increase our band­width.”

Current state-of-the-art fiber-optic communi­cations, like those used in Australia’s National Broad­band Network (NBN), use only a fraction of light’s actual capacity by carrying data on the colour spectrum. New broadband tech­nologies under development use the oscil­lation of light waves to encode data, increasing band­width by also making use of the light we cannot see. This latest tech­nology, at the cutting edge of optical communi­cations, carries data on light waves that have been twisted into a spiral to increase their capacity further still. This is known as light in a state of orbital angular momentum (OAM).

In 2016 the same group from RMIT’s Labora­tory of Arti­ficial-Intelli­gence Nano­photonics (LAIN) managed to decode a small range of this twisted light on a nano­photonic chip. But tech­nology to detect a wide range of OAM light for optical communi­cations was still not viable, until now. “Our miniature OAM nano-electronic detector is designed to separate different OAM light states in a conti­nuous order and to decode the infor­mation carried by twisted light,” Ren said.

“To do this previously would require a machine the size of a table, which is completely impractical for tele­communi­cations. By using ultrathin topo­logical nano­sheets measuring a fraction of a millimeter, our invention does this job better and fits on the end of an optical fiber,“ Ren said. LAIN Director and Associate Deputy Vice-Chan­cellor for Research Innovation and Entre­preneurship at RMIT, Min Gu, said the materials used in the device were compatible with silicon-based materials use in most tech­nology, making it easy to scale up for industry appli­cations.

“Our OAM nano-elec­tronic detector is like an eye that can see infor­mation carried by twisted light and decode it to be understood by electronics. This tech­nology’s high perfor­mance, low cost and tiny size makes it a viable appli­cation for the next generation of broadband optical communi­cations,” he said. “It fits the scale of existing fiber technology and could be applied to increase the bandwidth, or poten­tially the processing speed, of that fiber by over 100 times within the next couple of years. This easy scala­bility and the massive impact it will have on telecommu­nications is what’s so exciting.”

Gu said the detector can also be used to receive quantum information sent via twisting light, meaning it could have appli­cations in a whole range of cutting edge quantum communi­cations and quantum computing research. “Our nano-elec­tronic device will unlock the full potential of twisted light for future optical and quantum communi­cations,” Gu said. (Source: RMIT)

Reference: Z. Yue et al.: Angular-momentum nanometrology in an ultrathin plasmonic topological insulator film, Nat. Commun. 9, 4413 (2018); DOI: 10.1038/s41467-018-06952-1

Link: Laboratory of Artificial-Intelligence Nanophotonics, School of Science, RMIT University, Melbourne, Australia

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