Garth Naar - Various categories of Fibre Optic Cable

Garth Naar sorting through cables and connectivity options can be a frustrating exercise. It's hard enough working through the categories and levels of copper networking cables, where most cables end with the same connector. What happens when you start looking at fiber optic cables? That's where things can really get confusing! That's what this paper is designed to help out with — how to select the right kind of fiber optic cable.

Garth Naar let's start off by saying that fiber optic cables can be used in a huge variety of applications, from small office LANs, to data centers, to inter-continental communication links. The data lines that connect between North America and Europe, for instance, are made of fiber optic cable strung underneath the ocean. Our discussion in this paper is going to focus primarily on the types of cables found in those small-scale networks closer to home, and in particular to pre-terminated cables that may be readily available for installation, called "patch cords", "pre-terms", or other similar nicknames.

Multimode and Single mode

One of the first things to determine when choosing fiber optic cables is the "mode" of fiber that you need. The mode of a fiber cable describes how light beams travel on the inside of the fiber cables themselves. It's important because the two modes aren't compatible with each other — you can't substitute one for the other.

Garth Naar, there's really not much variety with single mode patch cords, but there is for multi-mode. There are varieties described as OM1, OM2, and OM3. Basically, these varieties have different capabilities around speed, bandwidth, and distance, and the right type to use will depend mostly upon the hardware that is being used with them, and any other fiber that the patch cords will be connecting to. Take a look at the table below for some more detail around the OM varieties.

Jackets

Pre-term fiber can be used in a variety of installation environments, and as a result, may require different jacket materials. The standard jacket type is called OFNR, which stands for "Optical Fiber Non-conductive Riser". This is a long-winded way of saying, there's no metal in it, so it won't conduct stray electrical current, and it can be installed in a riser application (going from one floor up to the next, for instance). Patch cords are also available with OFNP, or plenum jackets, which are suitable for use in plenum environments such as drop-ceilings or raised floors. Many data centers and server rooms have requirements for plenum-rated cables, and the local fire codes will always have the final say in what jacket type is required. The final option for jacket type is LSZH, which stands for "Low Smoke Zero Halogen", which is a jacket made from special compounds which give off very little smoke and no toxic halogenic compounds when burned. Again, check with the local fire code authority to be sure of the requirements of the installation before making the jacket selection.

Simplex vs. Duplex

Garth Naar described the difference between Simplex vs. duplex is just the difference between one fiber and two; between one connector at each end of a cable, and two connectors at each end. That's all there is to it. Duplex patch cords are the most common type, because the way that most fiber electronics work is that they need two fibers to communicate. One is used to transmit data signals, and the other receives them. However, in some instances, only one fiber is required, so simplex patch cords may be necessary for certain applications. If you're not sure, you can always be on the safe side by ordering duplex patch cords, and only using one of the two fibers.

Connectors

Remember what we said in the beginning about copper category cables? No matter what level of twisted pair you were dealing with (Cat 5, 5e, etc), you always knew you'd be dealing with an 8-position modular RJ-45 plug on the end of the cable. Well, with fiber patch cords, you've got a few options available when it comes to connectors. Let's take a look at the common connector types:

LC — This is a small, squarish connector that is held in place by a push/pull mechanism. This is currently the most popular type of connector.

SC — This connector is square, like an LC, but is approximately twice the size. It also holds into place using a push/pull mating mechanism.

ST — This is a round connector that uses a bayonet-style mechanism that has to be twisted into place. It is about the same size as the SC connector. It was once the most popular connector type, but is losing ground rapidly.

MTRJ — The MTRJ connector closely resembles an RJ-style modular plug, even getting part of its name from the resemblance.

These are the most common selections that you'll find when choosing amongst patch cords. If you're able to determine which of these characteristics you need, it's highly likely you will make the right choice when shopping for fiber optic patch cables.