New fibre optic technology promises breakthrough in Internet bandwidth
28 June 2013
A team of engineers has devised a new fibre optic technology based on optical vortices that promises a dramatic increase in Internet bandwidth.
Widely studied in molecular biology, atomic physics and quantum optics, optical vortices (also known as orbital angular momentum, or OAM, beams) were thought to be unstable in fibre, until Boston University's (BU's) Professor Siddharth Ramachandran designed an optical fibre that can propagate them.
He and Professor Alan Willner of the University of Southern California (USC) have demonstrated not only the stability of the beams in optical fibre but also their potential to boost Internet bandwidth.
"For several decades since optical fibres were deployed, the conventional assumption has been that OAM-carrying beams are inherently unstable in fibres," said Ramachandran. "Our discovery, of design classes in which they are stable, has profound implications for a variety of scientific and technological fields that have exploited the unique properties of OAM-carrying light, including the use of such beams for enhancing data capacity in fibres."
The reported research represents a close collaboration between optical fibre experts at BU and optical communication systems experts at USC. "Siddharth's fibre represents a very unique and valuable innovation. It was great to work together to demonstrate a terabit-per-second capacity transmission link," said Willner.
Ramachandran and Willner collaborated on this work with OFS-Fitel, a Danish fibre optics company, and Tel Aviv University.
Traditionally, Internet bandwidth has been enhanced by increasing the number of wavelengths of data-carrying laser signals transmitted via an optical fibre, where the signals are processed according to their frequency (or colour). Increasing the number of colours has worked well since the 1990s when the method was introduced, but now that number is reaching physical limits.
An emerging strategy to boost bandwidth is to send the light through a fibre along distinctive paths, or modes, each carrying a cache of data from one end of the fibre to the other. Unlike the colours, however, data streams of ones and zeroes from different modes mix together; determining which data stream came from which source requires computationally intensive and energy-hungry digital signal processing algorithms.
Ramachandran's and Willner's approach combines both strategies, packing several colours into each mode, and using multiple modes. OAM modes in these specially designed fibres can carry data streams across an optical fibre while remaining separate at the receiving end.
In experiments Ramachandran created an OAM fibre with four modes (an optical fibre typically has two), and he and Willner showed that for each OAM mode, they could send data through a one-kilometre fibre in ten different colours, resulting in a transmission capacity of 1.6 terabits per second, the equivalent of transmitting eight Blu-Ray DVDs every second.