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 Monday, February 27, 2006

A revision to a commonly used ITU-T Recommendation will extend use of fibre previously used mainly in core networks to metropolitan or regional networks. Crucially it also has the potential to greatly reduce operating costs for network providers.

G.655 for non-zero dispersion-shifted fibre (NZDSF) was originally designed to support DWDM long distance core, it was designed to reduce a phenomenon called four wave mixing (an interaction between wavelengths that generates additional optical channels). The impressive improvement in dispersion profiles afforded by G.655 fibre together with the development of the G.692 standard for optical interfaces for multichannel systems with optical amplifiers led to an explosion in the market for DWDM systems experts say.

Reduced dispersion allows sending signals over greater distances without dispersion compensation, meaning that operators will be able to avoid using a compensator and amplifier as well as the costs associated with this; power, protection, housing and security.

The revision to G.655 (full title, Characteristics of a non-zero dispersion-shifted single-mode optical fibre and cable) deals with chromatic dispersion, a phenomenon which at low levels counteracts distortion, but at high-levels can make a signal unusable. The management of chromatic dispersion is crucial as the number of wavelengths used in WDM systems increases. ITU has a history of providing the specifications that allow operators to most efficiently handle this. The revision allows more efficient use of the properties of chromatic dispersion by more stringently defining its existence. It defines chromatic dispersion in two new categories that can be exploited by systems designers as necessary.

The need for the work stemmed from systems' designers want to better understand dispersion. And a result is that experts saw a use for G.655 cable in metro or regional networks where it had previously only been used in core networks.