Advantages and Limitations of Optical Fiber Cable/ Communication

An overview of Optical Fiber Cables/ Communication is given in the above Infographics. You can find a more in-depth technical information about OFC here. There is also a nice flash presentation outlining the basics of Optical Fiber Cables/ Communications here. What you can expect to read in this article though, are the advantages and dis-advantages/limitations of Optical Fiber Cables/ Communication (especially over Copper UTP Cables) for creating Computer Networks.

Advantages of Optical Fiber Cable / Communications:

• Optical Fiber Cables can run massive distances like 40 KM or much more (Single Mode Fiber Cables) without having to repeat the signal anywhere in-between.
• Normally, the Optical Fiber Cables do not have speed limits or bandwidth limitations. They can support any speed/ bandwidth depending only on the type of optics (active components) used at either end. But the distance over which they can support such speeds varies for each fiber material.
• Its normally enough to replace the optics (active components) at either end in order to upgrade the fiber communication to support higher bandwidths. There is no need to change all the underlying cabling.
• Optical Fiber Cables support duplex communications (simultaneous upstream and downstream), but they use two cores for doing so. One core is used for Transmission (Tx) and the other core is used for Reception (Rx).
• Optical Fiber Cables are flexible and can be laid both within the buildings (Indoor Fiber Cables) and outside the buildings (Shielded Fiber Cables). In most of the cases, they are buried under the ground (with a depth of minimum 3 feet) using a Trench and protective materials.
• Multiple cores are built into each optical fiber cable(like 6/12/24 cores) and hence each optical cable can support multiple individual connections (3/6/12).
• Optical Fiber Cables are not affected by EMI – Electromagnetic Interference as they carry light, and hence can be used even for the most demanding industrial applications.
• They can also be used in lightning prone areas as they do not carry the electrical signals as such to affect switch ports, etc during a lightning.
• The danger of ignition during a fire is much less with optical fiber cables.
• There are optical taps that can be inserted in-between long running optical cables. There are two types of taps – Passive optical taps that do not require electrical power and are used for simple monitoring of OFC networks & Active optical taps that require electrical power and are used for manipulation or boosting of signals sent to the monitoring port.
• The low cost 850 nm Laser optimized 50/125 micro meter Multi-Mode Fiber (OM3 type) gives 10 GE performance for up to 300 meters. The optics associated with it are also moderately priced. So, these fibers can be used in the enterprise LAN segment for short distances, where the single mode optics might turn out more expensive. OM4 Laser Optimized Multi-Mode Fiber supports even higher bandwidths like 40/100 Gbps.
• Even if many fibers run along side each other, the chances of cross talk (and hence signal loss) is very less, unlike Copper UTP Cables.
• Wire tapping with Optical Fiber Cables is more difficult.
• Optical Fiber Cables (Especially Passive Optical Networks) are used for providing high speed broadband to homes, these days (FTTH).
• Trouble shooting an Optical Fiber Network is possible with equipments like the OTDR Tester (Optical Time Domain Reflectometer). Using this, one could measure the optical power loss and locate the faults caused due to fiber breaks, connectors or splicing.

Disadvantages/ Limitations of Optical Fiber Cable Networks:

• Optical Fiber cables have limited bend radius (about 30 mm). So, if they are bent more, it might lead to some signal loss. But recently, bend resistant fibers have been introduced which have higher tolerance to bending.
• Copper UTP cables can carry data as well as power. Some POE enabled IP devices like IP Phones, Wireless Access Points etc are powered directly using the UTP Cables/ POE switches. This, is not supported by the optical fiber cables as they carry only data.
• Unlike Copper UTP cables which have standard Rj-45 Jacks and connectors (mostly), optical fiber cables have many types of connectors and this lack of standardization adds confusion.
• By bending the normal optical fiber cables, some leakage of signal could be induced and that can be used for hacking the information in them. So, even though doing that might be difficult, they are not totally tamper proof.
• Single mode cables and their associated optics (active components) are very expensive. Even though multi-mode cables/ optics are less expensive, they are not even close to the costs of copper UTP cables/ ports. Moreover, multi-mode cables have restrictions in distance for supporting higher bandwidth (like 1 Gbps and 10 Gbps).
• There are outdoor fiber cables but they need to be shielded well. This shielding makes them less agile/ flexible to run in all the places and it increases the cost of cables as well.
• Fiber cables can not be directly terminated on to the network/ optical switches. They need a whole array of active/ passive components like SFP Modules, Fiber Patch Cords, appropriate connectors, Fiber Patch Panel (LIU), Pigtails and Couplers. All these components add the cost of fiber network implementation at each location.
• Each Core of the Optical Fiber cable needs to be spliced in order to complete the connection to the network/optical switch. Both the splicing equipment and the cost of installation (for splicing) per core is quite high.
• Fiber splicing is a complicated procedure and requires skilled manpower to achieve. If it is not done properly, there will be performance degradation.
• An outdoor shielded fiber cable cannot just be laid in a trench. It requires, at minimum, external HDPE pipe surrounding it over the entire length, bricks/ concrete slabs over the fiber cable/ HDPE pipe also extending the entire length through which they are laid, outdoors. This, no need to mention, further increases the cost.
• After installation and also during trouble shooting, the fiber cores need to be tested using testing equipments like OTDR. But these equipments are quite expensive to procure, and if rented, the charges for testing each core could be considerable.

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