Photonics in communication

Fibre optics are now a familiar feature of long-range communication. An optical fibre consists of a glass core and a cladding layer wrapping around it. The core and cladding are precisely chosen so that their refractive indices (the ability to bend light by specific amounts) ensure that the photons within the core are always reflected at the interface of the cladding (see Fig. 14.2).

This ensures that the only way light can escape is through the ends of the fibre. Either an LED or a laser sends electronic data that have been converted to photons along the fibre at a wavelength of between 1200 and 1600 nanometres. The most advanced fibres can send a light signal for about 50 miles without the need to boost the signal. Until the early 1990s the boosters were electronic, which created a bottleneck in the system. The answer was to insert stretches of fibre that were infused with ions of the rare earth element erbium. When the erbium-doped fibres are irradiated by a laser light the excited ions refresh the fading signal. This has resulted in dramatic improvements in capacity and speed - up to tens of gigabits per second. At the same time this refreshing facility can boost the power of many wavelengths simultaneously, so that it is now possible to send 160 frequencies in parallel and supply a total bandwidth of 400 gigabits per second over a fibre. Visible on the horizon is a fibre capacity of 300 to 400 terabits a second. New technology could break the petabit barrier (a petabit is ten to the power of fifteen bits). It will not come a moment too soon.

In February 2000 the computer network at Kent State University in the USA came to a virtual standstill when thousands of hits from the music file-sharing utility Napster invaded emails from the Vice Chancellor and research data on genetic engineering. This gives credence to the nightmare scenario that a video-Napster capable of downloading anything from Birth of a Nation to Rocky IV could bring down the entire Internet.1 On-line virtual reality could overwhelm the system with up to 10 petabits per second, which is 10,000 times greater than present-day traffic. Linked computers sharing power called metacomputing could require 200 petabit capacity.

The only transmission medium capable of meeting this challenge is a fibre optic system which is not inhibited by electronic switching. At present the problem is that the most advanced networks transmitting 10 billion bits per second threaten to choke the processing units and microchip memories in electronic switches. It's as though a ten-lane motorway suddenly contracts to a country lane. The gigabit tidal wave of photonic data has to be broken up into slower data streams that can be converted to electronic processing. Then the sequence has to be reversed to produce the fast flowing photonic mode. The answer is photonic switching, the holy grail of photonics research.

Eliminating the electronic stage of transmission has been the aim of Japanese scientists in Tsukuba. In May 2001 they claimed to have created an optical transistor that would pave the way for all-optical networks. Basically they have found a way to make one light beam make another disappear, thereby creating an optical semiconductor.

Huge amounts of venture capital are being directed at this developing field of science. In the first nine months of 2000 venture funding for optical networks totalled $3.4 billion. The attraction for this kind of investor is that the cost of transmitting a bit of optical information is halving every nine months.

Soon the whole world will be linked to an optical fibre superhighway based on photonic materials. One consequence is that teleworking will become much more prevalent, enabling commercial enterprises to scale down their centralized operations. High-capacity communication systems based on a multimedia super corridor accommodating audio, computer and visual communication will have a major impact on work patterns. Already teleconferencing is reducing the need for costly gatherings of executives as companies spread their operations globally. This will offer much greater freedom to employees as regards their place of abode.

The most recent development in IT is known as 'tele-immersion', described by Scientific American as 'a new telecommunications medium which combines virtual reality with videoconferencing. [It] aims to allow people separated by great distances to interact naturally as though they were in the same room' and 'involves monumental improvements in a host of computing technologies . . . Within ten years tele-immersion could be a substitute for many types of business travel'.2 Photonic switching is perhaps the most monumental improvement that heralds a quantum change in the architecture of computers which are already approaching the barrier imposed by the physics of electronic processing. Not only will this next generation of computers have vastly increased capacity, they will achieve this with a fraction of the power consumed by present day machines. They will also avoid the heat gains of electronic processors. So the combination of LEDs and photonic computers will dramatically reduce the energy requirements of a typical office building, not only in terms of lighting and computing load but also in reducing the cooling load on the ventilation system.

A note of caution to conclude this chapter. One outcome of the exponential development of IT is that the economic and business certainties of the twentieth century are disintegrating. As electronic commerce grows, governments will find it ever harder to raise taxes. Each day trillions of dollars move around the global money market as corporations locate their transactions in low tax jurisdictions. Add to this the fact that people are increasingly obtaining goods and services via the Internet from places with the lowest taxes and it is clear that national governments will have diminishing power to raise revenue, with obvious consequences for the social services.

One scenario is that the growing gap between the poor and the affluent will continue to widen. The dividing line will become sharply defined as between those with IT and communication skills who can keep up with the pace of change and those who increasingly fall behind in this new Darwinian environment. As Ian Angell (head of the Department of Information Systems, London School of Economics ) puts it:

People with computer skills are likely to end up winners. Those without are likely to emerge as losers. The power of the nation state will weaken. Communities that invest substantially in communication technologies will thrive. Those who don't, or those whose citizens are isolated from the new ways to communicate, will suffer. Change is inevitable. The Information Age will be kindest to those who adapt.3

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