Optical fibre cable laying

Cable laying along RATP's railtracks is carried out during passenger's traffic break between 1h30 and 4h30 am.
More often, cables are laid in gutters along the RER lines and hanged up on hooks along the metro lines. Cables installed by Telcité generally include 36 monomode fibres in 6 tubes of 6 fibres, which is a good modularity for ease of soldering as much as for possibilities to separate the tubes at delivery points.
There are today two methods for linking together two optical fibres : 1) Mechanical linking which most often includes the coupling of two connectors put end to end, and sometimes the linking by mechanical "Splice" which is used for repair after a circuit break. Optical distribution frames allow cross connect fibres from different cables, by means of connection leads (yellow) and optical connectors.
This operation is needed to make the different connections, some of them being exit points to the customer network. Attenuation for one point of connection (2 connectors and 1 connection lead) is less than 0,7 dB (at 1300 nm and 1550 nm).

2) Soldering :
This operation is done with an automatic soldering machine that ensures :- alignment of the fibre's core along the 3 axis,- visual display in real-time of the fibres soldering,- traction test after soldering (50 g to 500 g) ,- attenuation measurement at 1310 and 1550 nm ( 0,03 à 0,1 dB on average with a maximum of 0,15 dB).


An other technique for laying : blowing
Telcité lays its optical cables in cables trays generally made up of lines of hooks or gutters whose lids are removable. Another technique of laying, known as "blowing", is used for laying optical cables in roadways. Indeed, the cables can be "blown" in a tube made of HD-PE (High Density Poly Ethylen) itself laid at the bottom of a trench which is refilled after installation of multitube structures made up of n tubes. The optical fibre cable (10 mm to 15 mm in diameter) is then blown in the tube (about 50 mm in diameter using an air compressor which can propel it up to 2 kilometres away. This technique allows to lay the cables in the tubes only when needed.