Which Type of Optical Fibers are Used for Fiber Optic Data Cables?

Here is a query received from one of the visitors to this site. “I have one doubt regarding the application of FTTH cables and fiber optic data cables. I was a bit confused between the both. I like to clarify the difference between FTTH indoor cables and data fiber optic cables. I know that the fiber optic is the same but the construction of the cable for both applications is different”. 

“Can we use the same fiber optic cable for both applications? When I approached a fiber optic cable supplier’s engineer, he told me that they use their indoor cable for both types of applications. So could you please tell me the difference if any and the applications, equipment, etc. for each type of cable if at all there are any differences?”

The answer was Fiber optic data cables are used mainly for data communication as the name indicates. Computer networking in an office is the best example and simple application. The applications include remote control, temperature sensing, etc. Fiber optic data cables are used also with Medium voltage (MV) and High Voltage (HV) energy cables to provide remote control of rotor speed, blade angle, braking, temperature, hydraulic levels, etc. through distant programmable Logic controllers, abbreviated as PLCs.

The application area of fiber optic data cable demands mainly uses of Multimode fibers. Both 62.5/125 micrometer and 50/125-micrometer fibers are used according to the application. Multimode data fiber cables come with a mainly tight buffer design. i.e., 0.9 mm coated fiber. The coating material used again depends on the application like plenum or riser application. For Plenum, PVC with fire-resistant characters or LSOH material is used. There are polyester elastomeric materials for riser application. Multimode fibers have good bandwidth required for data communication for short distances up to 2 km for example.

FTTH application is slightly different. FTTH requires single mode fiber compliant with ITU T G.657A recommendations. Generally called Bend insensitive fiber, G.657A fibers are used to reach the last mile in the optical networks. The application area needs small cables with low and many bending capacities as there will be many curves in a home or apartment. The cable should be small enough to be placed in the Rosette or Wall mounted outlet. Indoor cables without bend insensitive fibers are not a good solution for FTTH application.

It seems the answer given above could not satisfy his actual doubts. After some days he came with some more doubts. He contacted his fiber optic cable supplier and they informed him that they stopped using multimode fibers due to the unavailability of multimode fibers. Now all the fiber optic cables make use of only single mode fiber even for data application. He wanted to know whether this is an accepted method or not? The fiber optic cable provider informed him that they supply fiber optic cables for metro, long haul, backbone and access networks, all singlemode fibers. He was interested to know which is the right fiber to be used and whether it is good to use single mode fibers for data cables.

Both single mode fibers and multimode fibers can be used for the transfer of data from one place to another place and that is called communication. The basic purpose of fiber optic cable is communication. It all depends on the distance of the fiber optic network and amount of data to be transferred and the cost of the total fiber optic system in order to decide on the type of optical fiber that is to be used in the fiber optic cable.

Generally, multimode fibers and G.657A fibers come at the last mile of the network. Multimode data cables are used in short distance data transmission. For example, a 2 km or intra-building fiber optic network.

Why Do Fiber Optic Installers Prefer Multimode Fiber for Short Distance?

Multimode optical fibers due to their property can not go more distance as many modes travel together get confused due to modal dispersion after a long distance. Also, optical components, light sources, and detectors, etc are cheaper compared to that for a single mode fiber.

Though the multimode fiber is a little bit costlier, which approximately US $ 40 to the US$ 45 per km data fiber optic cables need a few fiber counts like 4 to 24 fiber cables. The overall system cost using Multimode fiber is cheaper for short distance communication.

It is up to the installer when he calculates the power budget and total system cost to decide which fiber is suitable for his system. Of course for long distance data transmission, he has to go for singlemode fiber. For short distance data communication, optical component cost is predominant. Single mode fibers can carry a huge amount of data, but local area networks do not need to carry a very high amount of data like that in long haul communication. Local area network data can be carried by Multimode fibers.

All the above points will be taken care of by installation system engineers to decide on the type of fiber. For the long haul, metro, backbone, and access networks single mode fibers are used. Distance in all these cases will be more than 2 to 4 km from the OLT point to the end user fiber distribution hub. When the local area network distance is within 2 to 4 km, optical components prices are more important and the data amount is suitable for a multimode to carry, then the installer decides in favor of multimode.

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