Optical amplifiers

Date: 2015-10-07; view: 420.

Erbium doped fibre amplifier technology has made great strides in the last three years. By using such amplifiers at both ends of an optical link, it is possible to greatly increase the maximum distance between transmitter and receiver, with distances up to 300km being predicted for links that employ low loss optical fibre cables, (c.f. present day optical inks at 565Mbit/s which can typically span 40-70km). This great increase in span capability holds out the prospect of interconnecting the majority of large centres of popula­tion in Europe by unrepeatered line systems i.e. the line systems consist of two LTEs plus cable, without any intervening simple repeaters. (Drop and insert repeaters are a different case, as they are deployed to drop and insert traffic, rather than solely to boost the amplitude of the optical signals). The resulting extinction of con­ventional line system repeaters means that the SDH RSOH in the STMs will eventually become redundant for terrestrial systems.

In addition to this, there is also the future proofing that results from replacing a conventional, electronically regenerating repeater, with a repeater that merely amplifies the transiting optical signals. Optical amplifiers are largely hit rate independent, hence it should he possible to upgrade the capacity of a line system by merely changing the LTEs, and not the repeaters. This idea is particularly exciting for undersea line systems where a major part of the total system cost lies in the repeaters. Up till now, these have always been constrained to operate at a fixed bit rate.