INSIGHT ISSUE 02 | 2020

28 Enabling the Digital and Energy transition Piet Matthijsse, now retired fromDraka, suggested this bend-insensitivity technical issue: “I had worked for Dutch telecom incumbent KPN which gave me a great understanding of the issues cable users faced. I had seen there was often no alternative but to bend or twist fibres in large buildings. We had also experimented with adding “We soon saw that using these bend-insensitive fibres in connectivity products such as ODFs, splice closures and wall boxes meant that less space was needed for components, which is very important in FTTH networks with its high fibre densities. The robustness of the fibre made it possible to save great deal of money on installation and helped avoid rework. The market didn’t take a great deal of convincing. People immediately understood the benefits and sales were excellent right from the start.” Frans Gooijer, Marianne Bigot, Pierre Sillard, Louis-Anne de Montmorillon SPECS A unique product \ Bend-insensitive fibre \ Trench-assisted design \ Fully in line with ITU-T recommendation G.652.D \ Fibre radii as low as 7.5 mm fibre to the local loop. That provided an opportunity to see which difficulties installers would typically encounter.” Louis-Anne de Montmorillon, now at Prysmian Group Fibre R&D in Douvrin, France, solved the technical challenge: “I had already been working in fibre design for some years and was able to adapt the trench concept to standard single mode fibres, in order to reduce bend losses by a factor of ~100 without impacting the other characteristics. This allowed for full compliance with the single mode fibre type, which was already installed worldwide in vast quantities.” A key challenge involving the R&D teams in Marcoussis and Douvrin was ensuring all relevant standards were met. For example, the mode-field diameter of the fibre had to be large enough not to introduce splice and incoupling losses, and the higher-order modes had to be contained to avoid interference with the fundamental mode and preserve ‘single-modeness’. A unique bend-insensitive fibre with a trench-assisted design was developed, fully in line with ITU-T recommendation G.652.D of standard single mode fibres for compatibility with the installed base. Bending characteristics were made compatible with the newly introduced ITU-T recommendation G.657. Even at fibre radii as low as 7.5mm, fibre lifetime was not a concern. After successful tests, the new optimized product was presented at the European Conference on Optical Communications, ECOC, in September 2006 and two months later at the 55th International Wire & Cable Symposium. Product and process developments lead to multiple follow-up patents related to further improvements and fine- tuning. Draka was asked critical questions regarding cable durability, but had carried out plenty of tests and could convincingly explain lifetime would not be an issue.