It is estimated that more than 5 billion optical fiber kilometers are installed on the earth including all kind of installations such as Submarine, Aerial, underground and premise. This number can be roughly converted to 138 million cable kilometers if we consider an average fiber count of 36 fibers per cable. With the progress of fiber to the home projects, this average will further go down since the premise cables are of smaller fiber counts. Higher count cables are mostly deployed in backbone/metro core networks. Extremely high count cables are utilized for data centers, but the lengths are limited. Recent reports from Prysmian shows development of 6912F cable for datacenter application.
Submarine cables have smaller fiber counts typically in the range of 6 to 12. Submarine cable system utilizes latest transmission technologies to achieve highest possible data transmission speeds and capacity over a single fiber. Long distance communication lines are made of typically from 24 to 48 fiber count cables. Metro-core/backbone networks utilize high fiber count cables typically in the range of 144 to 576 fibers per cable. In extremely high density population areas this number goes up to 1000 to 2000 fibers per cable.
As the number of fibers in a cable goes up, the chances of fiber break also goes up. Recent studies conducted to analyze fiber breaks throw light to this direction. It is estimated that more than at every 1 (one) minute 1 (one) fiber break occurs per 1000 kilometers of installed cable daily worldwide. Higher the number of fibers in a cable, higher will be the probability of fiber breaks. This not only indicates the higher probability of fiber breaks on high fiber count cables, but also indicates to the higher construction/digging activities in the metro area.
Number of fiber breaks in one day worldwide is estimated to be around 1566 on a rough calculation based on studies conducted by FCC in 2002 and the total fiber cable kilometers installed so far. Survey findings have revealed that on an average it takes around 4 hours to rectify/repair and bring back the network to its original condition. For submarine cables, it may take days or even weeks, depending on the damage. Almost 70% of the recovery time is spent to identify the nature and location of the fault. 30% of the recovery time is spent to do the actual repairing work.
Metro/backbone networks suffer mostly due to mistakes in construction work. Location of Installed cables are either unknown or wrongly informed to the construction workers. If the installed cable locations are not properly marked, inadvertent mistakes may happen from the installation crew. Premise area is more sensitive to fiber breaks since the fiber enters home and is in the middle of daily life and movements. ITU-T recommendations categorize bend insensitive fibers for premise application. Apart from lower attenuation increase with smaller bends, bend-insensitive fibers, that are categorized as ITU-T G.657A fibers, have higher resistance to the bending and therefore lower chance for break compared to the conventional fibers (G.652D).