Which optical cable to choose according to your FTTP architecture?
The subscribers’ connection to very high speed networks is performed by telecom network engineers with the use of various FTTP solutions. FTTP cabling is needed to link different optical points, e.g. to connect an OTO to the ISP box. Choosing the right fibre optic cable is not an easy job: depending on the cable mode, its structure and the type of connectors, the choice of an optical cable can be made among different types.
The selection of an optical jumper involves various steps:
Etape 1 – Choisir le type de fibre optique
The mode corresponds to the transmission mode of the optical light: this can be singlemode or multimode.
A multimode cable enables several light modes to pass through so to transmit different data. The OM1 structure has a 62.5 micron optical core while the OM2, OM3 and OM4 structures have a 50 micron optical core.
OM1 and OM2 optical cords are generally used for short distance Ethernet networks: these are fibre optic older generations, orange coloured. OM3 and OM4 are more commonly used today and support higher data rates over longer distances. They are turquoise and magenta, respectively.
A singlemode cable, with its 9-micron optical core, offers much higher performances than multimode fibres. Yellow coloured, these cables are mainly used for telecom applications such as the rollout of high-speed networks over large areas.
Step 2 – Choosing the cable type
Whether multimode or singlemode, the optical cable comes in simplex or duplex versions depending on the intended use. The simplex version consists of a single fibre core, whereas the duplex version presents two. As simplex fibre is based on a single fibre optic, it allows data to be transferred in one direction at high speeds. Duplex fibre, on the other hand, allows for bi-directional data communication and is ideal for telecommunications applications.
Step 3 – Choosing the cable structure
There are two fibre optic structures: tight buffered and loose tube. In the case of tight buffered structure, all the fibres are covered with a plastic layer that increases the outer diameter from 250 to 900 microns. In the case of a loose tube structure, fibres are enclosed by a tube, in packs of 4 to 24.
For fibre optic tight buffered structures, the optical connectors are easier to assemble. Indeed, they are to be mounted directly on the fibre, whereas in the case of a loose tube structure, pigtails are needed, so the connectorisation requires various tools such as splice trays and a fibre optic fusion splicer.
250µm loose tube fibre optic cable
900µm tight buffered fibre optic cable
Low shrinkage and high tensile strength
Resistance to mechanical stress
Resistance to extreme temperatures
LSZH retardant polymer
Improves the system performance
High tensile strength
Good mechanical and thermal performances
Fibre glass resistance
Step 4 – Choose the cable diameter
Step 5 – Choose the connectors
The optical cord is equipped with optical connectors at each end so to allow the alignment and coupling of optical fibres and ensure a good light transmission. There are many different types of connectors, but only few of them are used on a daily basis. They can be singlemode or multimode, depending on the transmitting medium. Among the most commonly used connectors, we can find the SC, LC, FC and ST versions.
The SC connector with 2.5mm ferrule is a push-pull connector. Being a low cost solution and easy to use, this connector is very popular.
The LC connector present the same properties as the SC, while also having a ferrule diameter twice as small, which makes it easier to use in difficult to access places.
The FC connector is mainly used with singlemode optical jumpers. It is equipped with a 2.5mm ferrule and a high-pressure ceramic tip.
The ST connector is used with multimode optical jumpers. It includes a 2.5 ferrule, a ceramic tip and a locking system that prevents the connector from being over-tightened in order to avoid all fibre damaging.
Step 6 – Choosing the length of the optical cord