30 April 2004, Geneva - ITU has set a global standard for a new optical fibre that will make it easier for network operators to
deploy bandwidth to maximise technology in core networks. The development of standards in this area is important if network
operators are to reduce costs and provide more innovative services to customers.
"G.656 is another significant step in the evolution of optical networks, because it allows a more economical deployment of optical
transport networks", says Peter Wery, Chairman of ITU-T Study Group 15 responsible for the Recommendation.
The new standard – Recommendation G.656 – will allow the easier deployment of Coarse Wave Division Multiplexing (CWDM) in
metropolitan areas, and increase the capacity of fibre in Dense Wave Division Multiplexing (DWDM) systems. Wave Division
Multiplexing (WDM)increases the data carrying capacity of an optical fibre by allowing simultaneous operation at more than one
wavelength.
G.656 allows operators using CWDM to deploy systems without the need to compensate for chromatic dispersion, a phenomenon that at
low levels counteracts distortion, but at high-levels can make a signal unusable. Although complicated, the management of chromatic
dispersion is crucial as the number of wavelengths used in WDM systems increase. ITU has a history of providing the specifications
that allow operators to most efficiently handle this.
G.656 also means that at least 40 more channels can be added to DWDM systems. In this case chromatic dispersion is used to control
harmful interference over this – unprecedented – range of the optical spectrum.
Note to technical editors:
The most important new feature in Recommendation G.656 fibre is the chromatic dispersion coefficient. In G.656 this coefficient has
an allowed range of 2 to 14 ps/nm*km in the 1460-1625 nm band, compared to 1 to 10 ps/nm*km for G.655.B and G.655.C which is only
related to the 1530-1565 nm band. This low value of the chromatic dispersion coefficient in the S-C-L bands is the real novelty of
G.656 because it allows the utilization of a larger wavelength band.
The other characteristics are very similar to previous Recommendations. The range of mode field diameter permitted in G.656 of 7 to
11 µm compares to 8 to 11 µm in the G.655 non-zero dispersion-shifted fibre. G.656 fibre has a maximum PMD link design value of 0.20
ps/sqrtkm, which is the lowest value recommended by ITU-T (the same value that ITU-T recently adopted for G.655.C). G.656 has the
same cable cut-off wavelength and cable attenuation coefficients in the C and L bands as G.655.
ITU-T G.656 (Characteristics of a fibre and cable with Non-Zero Dispersion for Wideband Optical Transport) is the most recent in the
G-series which specifies the geometrical, physical, mechanical and transmission characteristics of the optical fibres. Other
Recommendations in this series include:
- ITU-T G.652 - Characteristics of a single-mode optical fibre and cable
- ITU-T G.653 - Characteristics of a dispersion-shifted single-mode optical fibre and cable
- ITU-T G.654 - Characteristics of a cut-off shifted single-mode optical fibre cable
- ITU-T G.655 - Characteristics of a non-zero dispersion-shifted single-mode optical fibre and cable
For further information:
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