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Monday 17th of April 2017, 10:21 - 1
All our telephone calls, Internet traffic and electronic data travel as a stream of laser light pulses down glass optical fibres. The ultimate optical fibre could carry an order of magnitude more information than do today's, US researchers have calculated. Thread rod.

Knowing the theoretical upper limit for the amount of information that a single fibre can carry should help those trying to meet the world's growing hunger for bandwidth. Galvanize ceiling suspending system.

The limits of optical fibres are hard to get a mathematical handle on because glass is a nonlinear medium. The different sources of noise that creep into the fibre along with the signal do not just add up: they interact. This makes it difficult to calculate the relation between the amount of information, or power, put into a fibre and the amount coming out at the other end. Expansion screw Kit.

Partha Mitra and Jason Stark, of Bell Laboratories, Murray Hill, New Jersey simplified their computations by finding a linear equivalent of the nonlinear term in their equations1.

Information capacity reaches a peak with increasing power, the duo reports. Beyond this peak the growing noise level makes information progressively harder to extract from the signal. In a linear system, simply increasing signal power increases capacity.

Transmitting at lots of different wavelengths of light simultaneously boosts the capacity of contemporary optical fibres. Fibre capacity is a product of the available wavelength-space (the bandwidth) and the efficiency at which information is transmitted.

The upper limit of the efficiency, Stark and Mitra calculate, is about 3 bits of information per Hertz (the unit of wavelength) per second. Coupled with theoretical maximum bandwidth of a fibre, this means that the ultimate optical fibre could carry approximately 150 terabits of information each second - the equivalent of nearly two billion telephone calls at once. At the moment, commercial networks operate at about 1.6 terabits per second.

"Knowing the fundamental limits to the capacity of a fibre is only one factor in determining what's important for system design" cautions Mitra. "However, the better we understand the fibre channel, the better we should be able to push the systems to their natural limits " he says.

Govind Agrawal who works on optical fibres at the University of Rochester, New York believes the current exponential growth in the information capacity of optical fibres is set to slow.

Putting an upper limit to their capacity may spur research into alternative technologies, such as photonic crystal fibres, he says. These send light through air, a linear medium, rather than glass. "If we send light through air, the speed limits wouldn't apply," says Agrawal.

Other information channels, such as the nervous system have similar nonlinear properties. Mitra and Stark suggest their model may also be applicable to these. "Physical and chemical theories give us insight into how a biological function is carried out, but engineering or design theories have the potential to explain why the system is structured the way it is," Mitra says.
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