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Reduced-diameter, high-density research yields 180μm-coated bend-insensitive fibre

diameter fibres

Reduced-diameter, high-density research yields 180μm-coated bend-insensitive fibre

In a new report, Prysmian documents the design and fabrication of a 180μm-coated bend-insensitive fibre with standard 125μm cladding.


High-density cables can help meet capacity demands and make installations faster, more cost effective and environmentally friendly. Prysmian’s innovation has excellent optical and mechanical properties and is fully compatible with legacy 245μm- and 200μm-coated fibres. A 576-fibre micro-duct cable with an 8.2mm diameter, yielding a record fibre density of 10.9fiber/mm² for such cables, was also fabricated.

Ways to increase cable density with fibres.

  • Space-division-multiplexed fibres with standard 125μm cladding diameter. However, there are cost and connectivity challenges ahead before these solutions become practical.
  • Reducing the cladding diameter to 80μm with coating diameters around 160μm. These fibres suffer from increased micro-bending sensitivity (factor of ~10 compared to standard 125μm-cladding fibres with same other properties) and still face connectivity and handling challenges.
  • Keeping a standard 125μm cladding diameter and reducing the standard 245μm coating diameter. There have been impressive cable demonstrations fitting 6,912 fibres into a 50mm duct (https://na.prysmiangroup.com/media/press-releases/PG-NA-first-to-produce-6912-fiber), using 200μm coated fibres introduced over a decade ago. Preliminary studies of <200μm coated fibres have been reported but work on index-profile designs and coating materials is needed to make them suitable for cabling. Prysmian designed and manufactured an optimized fibre with 180μm coating diameter using this third approach. A trench-assisted step-index profile, that had long proven effective in reducing bending sensitivities, was chosen.

Properties of 180μm-coated bend-insensitive fibre with 125μm cladding diameter

  • Fully compliant with ITU-T recommendations G.652.D and G.657.A2
  • Microbending sensitivity similar / better than 245μm and 200μm coated fibres.
  • Can be spliced with legacy fibres using conventional tools and fusion splicers. Fusion splicing tests proved full backward compatibility with legacy fibres. Tests ensured that no problems exist with the 180μm coated G.657.A2 trench fibre and verify backward compatibility with 245μm- and 200μm coated fibres.
  • Excellent mechanical reliability. The 180μm-coated G.657.A2 trench fibre meets all existing requirements for stripping, tensile strength, and fatigue properties (in accordance with IEC 60793-2-50 for type B fibres). There was no difficulty in cleanly stripping the 180μm coatings with commonly used tools.
  • Strength at 50% probability of breakage was always above the 550kpsi lower limit specified by the Standard, before and after aging treatments.
  • The smallest 180μm diameter has a cross-section about half of that of 245μm coated fibres, for tighter fibre packing densities and cable miniaturization.
  • A 576-fiber micro-duct cable with a diameter of 8.2mm, yielding a record fibre density of 10.9fiber/mm² for such cables, was successfully fabricated.

“The challenge was to maintain a significant buffer layer of soft primary coating for protection against micro-bending while preserving an adequate secondary coating thickness to allow handling robustness and mechanical protection,” explains Pierre Sillard, Fibre products R&D Manager at Prysmian Group. “We managed to reduce the micro-bending sensitivity by a factor of ~2, compensating for a reduction of the primary coating diameter. We reduced this to 150μm and decreased the thickness of the coloured secondary coating. As expected, the 180μm-coated G.657.A2 trench fibre showed almost no degradation when compared to the 200μm-coated G.657.A2 trench fibre. It also performs better than the 200μm-coated G.652.D non-trench fibre.”

Pierre Sillard

Fibre products R&D Manager at Prysmian Group

“Given the excellent optical and mechanical performance of the 180μm coated bend-insensitive fibre, we fabricated several micro-duct cables with 192 to 576 of such fibres. Their standard structures are based on loose tubes with a diameter of just 1.2mm, each containing 24 fibres, around a central strength member. The 576-fibre cable has a 8.2mm diameter yielded a density of 10.9 fibre/mm² – a record for such cables - and a weight of only 66kg/km. It is compliant with IEC 60794-1-21 optical and mechanical specifications.”

Adrian Amezcua, Optical Fibre Product Line Manager, adds: “A critical temperature cycling test confirmed the practical use of the cable. It can be installed into an 10mm inner diameter duct where previously it was only possible to install 432 fibres with 200μm coating diameter (<8.2fibre/mm²) or 192 fibres with 245μm coating diameter (<4fiber/mm²). With the 180μm-coated bend-insensitive fibres, up to 50% smaller microducts can be used to deploy the same number of fibres. These smaller ducts offer other significant advantages: up to 50% less polyethylene material used for fabrication, faster installation, and longer lengths (~70%) on a drum, reducing the numbers of drums needed for a project.”

Adrian Amezcua

Optical Fibre Product Line Manager