Disadvantages of Fiber-Optic Cabling

With all of its advantages, many people use fiber-optic cabling. However, fiber-optic cabling does have a couple of disadvantages, including higher cost and a potentially more difficult installation in some cases.

Cost

It's ironic, but the higher cost of fiber-optic cabling has little to do with the cable these days. Increases in available fiber-optic cable–manufacturing capacity have lowered cable prices to levels comparable to high-end UTP on a per-foot basis, and the cables are no harder to pull. Modern fiber-optic connector systems have greatly reduced the time and labor required to terminate fiber. At the same time, the cost of connectors and the time it takes to terminate UTP have increased because Category 5e and Category 6 require greater diligence and can be harder to work with than Category 5. This is even more of a concern for Category 6A and STP cabling. So the installed cost of the basic link, patch panel to wall outlet, is roughly the same for fiber and UTP.

Here's where the costs diverge. Ethernet hubs, switches, routers, NICs, and patch cords for UTP are relatively (no, not relatively, very) inexpensive. A good-quality UTP-based 10/100/1000 autosensing Ethernet NIC for a PC can be purchased for less than $25. A fiber-optic NIC for a PC costs at least four times as much. Similar price differences exist for hubs, routers, and switches. For an IT manager who has several hundred workstations to deploy and support, that translates to megabucks and keeps UTP a viable solution. The cost of network electronics keeps the total system cost of fiber-based networks higher than UTP, and ultimately, it is preventing a mass stampede to fiber-to-the-desk. This is why hierarchical star, the typical topology in a commercial building, involves running fiber backbone cabling between equipment and telecommunications rooms or enclosures, and copper UTP horizontal cabling between telecommunications rooms or enclosures and telecommunications outlets near workstations. However, optical fiber offers some options in network topologies that can make the overall network cost lower than a traditional hierarchical star network wired with more copper cabling (also see TIA's Fiber Optics LAN Section: www.fols.org).

Installation

Depending on the connector system you select, the other main disadvantage of fiber-optic cabling is that it can be more difficult to install. Copper-cable ends simply need a mechanical connection, and those connections don't have to be perfect. Most often, the plug connectors for copper cables are crimped on and are punched down in an insulation displacement connector (IDC) connection on the jack and patch-panel ends.

Fiber-optic cables can be much trickier to make connections for, mainly because of the nature of the glass or plastic core of the fiber cable. When you cut or cleave (in fiber-optic terms) the fiber, the unpolished end consists of an irregular finish of glass that diffuses the light signal and prevents it from guiding into the receiver correctly. The end of the fiber must be polished with a special polishing tool to make it perfectly flat so that the light will shine through correctly. Figure 1 illustrates the difference between a polished and an unpolished fiber-optic cable end. The polishing step adds extra time to the installation of cable ends and amounts to a longer, and thus more expensive, cabling-plant installation.

 
Figure 1: The difference between a freshly cut and a polished end

Connector systems are available for multimode fiber-optic cables that don't require the polishing step. Using specially designed guillotine cleavers, you can make a sufficiently clean cleave in the fiber to allow a good end-to-end mate when the connector is plugged in. And, instead of using epoxy or some other method to hold the fiber in place, you can position the fibers in the connector so that dynamic tension holds them in the proper position. Using an index-matching gel in such connectors further improves the quality of the connection. Such systems greatly reduce the installation time and labor required to terminate fiber cables.