| Popis: |
It has been clear for some time that optical fibre transmission systems have the potential to carry vastly greater amounts of traffic than they are currently used for. For example, in Fig.1, we show typical values for the insertion loss of a 50km fibre section in the 1500nm window and overlay it with an approximate representation of an Erbium Doped Fibre Amplifier (EDFA) gain spectrum. The combination promises transparency over a spectral window of about 35nm width, corresponding to a spectral bandwidth of approximately 4700 GHz. Dispersion in the fibre seems likely to limit the data rate transmitted over long distance circuits (say 1000km) to the region of 1 Gbit/s unless optical equalisation techniques are employed or special low dispersion (dispersion shifted) fibres are employed. Moreover, it is clear that at the terminations of any long haul system, the signals will be reconverted to electrical form. Two questions have thus presented themselves to us. How can this awesome potential of the fibre be better used and, at the same time, how can such higher capacity signals be routed and distributed through a complex multinode network in a flexible manner without returning them to the electronic domain? This latter question raises key points about how the signals will be multiplexed in the optical domain. |
