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ANALYSIS OPINION
diameter coating protects the glass fibre from mechanical damage and stress. Tis coating also protects the light-carrying capability of the glass by shielding it from mechanical forces that otherwise could cause small deviations in the axis of the core, leading to loss of optical power through the mechanism known as microbending. To enable tighter packing of fibre in the
cable, the coating diameter of the new generation of single-mode fibres has been reduced from 250µm to 20µm while still retaining the same 125µm cladding diameter of conventional single-mode fibres (see Figure 1). To compensate for the reduced coating thickness that could lead to more microbend loss, a ITU-T Recommendations G.657 compliant glass design is used as these fibres provide enhanced microbend resistance as well as superior macrobend performance. Further, the use of a superior coating provides resistance to microbend inducing external stresses – even when applied at the lowest thickness. Tere are three sub-categories defined by
the ITU-T Recommendation G.657 (G.657.A1 or ‘bend -improved’ fibres, G.657.A2 or ‘bend- tolerant’ fibres and G.657.B3 fibres or bend- insensitive fibres). As might be expected, the macrobend performance of each category is also reflected in the microbend tolerance. Tis leads to a selection decision for network owners wanting to take advantage of 200 micron fibres – what category of bend resistance is sufficient to ensure low- loss installation? G.657.A1 fibre is intended for use in outside plants and has been enthusiastically adopted by network owners[4]
. G.657.A2 and
G.657.B3 compliant fibres are more commonly used inside the building where much tighter bends on low fibre-count cables are oſten encountered and an improved bend performance may be required as a consequence.
Furthermore, the optical core profile design
that is frequently used to yield outstanding bend performance of G.657.A2 and G.657.B3 fibres can result in difficulties when attempting to splice in high volume in the outside plant when using established splicing programs and installation practices. Complimented by a suitably resilient coating material, G.657.A1 200µm fibre can deliver enough microbending resistance for outdoor applications to overcome challenges presented by the thinner coating application. Based on this understanding, Corning has
developed ClearCurve 200 fibre: a full- spectrum single-mode fibre with enhanced G.657.A1 macrobending performance and a mechanically strippable, UV-cured, Corning CPC acrylate protective coating, perfect for outside plant applications.
Making the most of 200-micron fibres Te smaller cross-sectional area of 200 micron fibres can enable either higher fibre count in the same cable cross-section or smaller cable cross-section maintaining the same fibre in a lighter package, both
delivering practical benefits for operators: l Increased fibre capacity within the existing duct infrastructure;
l Re-utilisation of the duct infrastructure to avoid expensive additional trench digging;
l Reduced costs for operators that lease ducts based on space occupied by the cable; and
l Extended blowing distances and reduced installation time in already crowded ducts. Telecom Italia, for example, has opted for
these reduced coating 200-micron fibres, recognising their potential to develop high-density cables without increasing the external diameter, therefore remaining compatible to current minicables and microducts[5]
200-micron fibres by reusing partially filled ducts, alternative operators can use 200-micron fibres to reduce duct leasing costs. In many European countries, regulatory bodies oblige their incumbents to provide access to their duct infrastructure, yet leasing prices are expensive. In some cases, duct rental is actually based on cross sectional area, in Europe this is the case in Portugal[6]
and France[7] . Based on published data about duct leasing fees in Portugal[8] a 50
per cent smaller cross-sectional area obtainable using 200 micron fibres could deliver cost savings of typically up to €800 per cable km (NPV of 25-year savings in duct leasing fees).
Conclusion 200 micron fibres have an important role in the trend for miniaturisation of FTTH hardware and cable. Te smaller and higher density cable designs that these fibres enable can have significant benefits in CapEx and OpEx network cost for both incumbents and alternative operators. Te bend resistance of G.657.A1-based 200 micron fibres is sufficient for a wide range of outside plant cable designs and applications, and their optical core profile technology makes these fibres compatible with existing G.652.D legacy networks and standard installation practices.l
Bibliography [1]
FTTH Council (2012). The Cost of Meeting
Europe’s Network Needs, Retrieved from http://
www.ftthcouncil.eu/documents/Reports/Cost_ Model_Report_Full_Version.pdf [2]
it cut the cost of fibre to the home?, Retrieved from
http://www.strategies.nzl.com/ wpapers/
2008019.htm [3]
and avoiding trenching. While incumbent operators will mostly benefit from
optical fibre and cable, Retrieved from http://
www.itu.int/rec/T-REC-G/en [4]
Network Strategies (2008). Micro-trenching: can
ITU-T (2009). Characteristics of a single-mode Mack, R. (2013). Commenting on Ruderman’s
“Fibre in Europe bucks economic trends”, Lightwave. Retrieved from http://www.
lightwaveonline.com/articles/2013/01/fibre-in- europe-bucks-economic-trends.html [5]
Billoti, M. (2012). Evoluzione Della Rete Di
Accesso Fissa, Notiziario Tecnico Telecom Italia, 2, 115 [6]
CSMG (2010). Economics of Shared
Infrastructure Access. Retrieved from http://
stakeholders.ofcom.org.uk/binaries/ consultations/wla/annexes/csmg.pdf [7]
ARCEP (2010). ARCEP publishes a decision that
sets the economic terms governing access to France Telecom ducts [Press release]. Retrieved from
http://www.arcep.fr [8]
Ofcom (2010), Economics of Shared Cross sections of conventional and 200-micron fibres
Infrastructure Access. Retrieved from http://
stakeholders.ofcom.org.uk/binaries/ consultations/wla/annexes/csmg.pdf
Issue 5 • Autumn 2014 FIBRE SYSTEMS 13
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