A perfect stream of video delivered down your broadband connection without irritating blips may seem as likely as uncovering the elixir of youth. Now a team of optical engineers think they have discovered the secret to both. They鈥檝e devised a way to revitalise light signals being sent down optical fibres, enabling them to send more information down the wires.
Bandwidth-hungry video streaming applications are prompting changes in the way that information is sent across the internet via its network of optical fibres. Conventionally, data is sent as a series of on-off light pulses, where each pulse encodes a single bit of information. More data can potentially be squeezed onto a stream of light by modifying the phase of each light pulse in a measurable way. Even greater carrying capacity can be achieved using light at several intensity levels, potentially 鈥渁n order of magnitude鈥� higher than now, says at the University of Southampton, UK.
However, light signals are gradually distorted by interacting with the fibre 鈥� a process known as attenuation. The more complex the signal, the harder it becomes to resolve after attenuation. What is needed is a way to reverse the degradation process and recreate the original signal, says Richardson, and his team has now developed one.
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Mix it up
Their device makes a copy of the attenuated incoming signal, and 鈥渕ixes鈥� it with a laser beam in a length of specially designed optical fibre. This generates two additional strong signals that are perfectly in phase with the data signal, one with a frequency just higher than the original and one with a frequency just lower. These signals can then act as a scaffold that, after interaction with a second copy of the data signal in a second fibre, removes the noise and generates a pristine version.
The team has demonstrated the technique on signals at 40 gigabits per second, but Richardson says it should handle higher data rates too.
Similar systems have been demonstrated before, but only in a 鈥渧ery controlled way where the phase and carrier frequency of the incoming signal are known鈥�, says Richardson. The new device can reconstruct an incoming signal without this information 鈥� a more likely scenario in the real world.
Phased approach
The current version works with relatively simple signals where the information is encoded into one of two light phases 鈥� so called 鈥渂inary phase-shifted keys鈥� (PSK).
鈥淥ur primary interest is in extending the approach to work with more complex signals such as quadrature PSK鈥�, which can encode more data in the phase, says Richardson.
A team led by at the University of Central Florida in Orlando has demonstrated components of the device separately, but not combined them into a fully functioning system. 鈥淭he results they demonstrated are quite impressive,鈥� he says.
Journal reference: Nature Photonics, DOI: 10.1038/nphoton.2010.203
