Optical Fiber – CompTIA A+ 220-1101 – 3.1

We rely on fiber optics to connect our high-speed and high-bandwidth network links. In this video, you’ll learn about the construction of a fiber optic cable and how multimode and single-mode cables are used on today’s networks.

Many of us use ethernet over twisted pair copper cabling, but there are ethernet standards that support communication over optical fiber. This is transmission by light. We are sending light signals down one side of the fiber, receiving the light on the other side, and that is the way we’re able to transmit data very long distances without any type of copper cabling.

Another characteristic of fiber optic communication is because we’re sending light signals, there’s no radio frequencies. This also means that we’re a bit more secure, because there’s no radio frequencies that could be intercepted by someone else to be able to see what traffic was going over that network.

And as you’re also probably aware, you can send light signals a very long distance, much longer than you could over a copper cable. Radio frequencies tend to have a shorter distance than fiber optics. This means that communicating over fiber optics can be done to a distance that’s much farther than you can communicate using copper cabling.

And if there’s any radio frequencies in your immediate area, they’ll have no impact on the signal going across the fiber optic network. This means if you’re in a manufacturing environment where there is a lot of radio frequency in use, then you can run fiber instead of copper and not have to worry about any of that equipment interfering with the signal on your fiber optic.

Here’s a picture of the fiber optic connection. You can see the fiber itself is very, very small, especially compared to a copper cable, and the actual fiber is a small that’s on the very end of this ferrule that’s protecting the fiber optics.

On the inside is the fiber itself. This is where we might have a light source, such as a light emitting diode, that is sending the light signal from one side of the fiber to the other, where it’s received by the equipment on the other side. The light is bouncing through this particular fiber, all the way through that core, and to the other side.

Around this core is cladding, which has a low reflective index, which means that any light that happens to hit the cladding is usually absorbed by the cladding instead of being reflected back in through the core. Around all of this we have a buffer coating, which protects everything that’s on the inside of that fiber optic cable.

If we look at the end of a fiber optic connection, there’s usually a ferrule, which is very often a large ceramic protector that goes around the fiber optics. And inside of that ferrule is the core of the fiber itself. You can see in this image it’s a very dim circle that’s right in the middle. I’ll highlight the middle, just so you can see where that particular fiber is. And if we remove that highlighting, you can now see where that fiber connection is in the middle of this connector.

There are two broad categories of fiber optic cable– a multi-mode fiber and a single-mode fiber. Multi-mode fiber is commonly used for short range communication. And in the world of fiber optics, short range means anywhere up to about two kilometers in distance. Each networking standard has its own set of maximum distances that you can use, depending on what type of cabling you’re using.

Multi-mode fiber tends to have a relatively inexpensive light source, so commonly we’ll see LEDs being used to send that light through the optical fiber. We refer to this as multi-mode fiber, because when we put the light into one end of the fiber, it is large enough so that multiple reflections can occur as that light is moving through the fiber. Those multiple reflections or multiple modes make their way through the fiber by bouncing back and forth through the core and then being collected on the other side.

Single-mode fiber is used for much longer distances, and there are some network standards that can support up to 100 kilometers in distance without needing to regenerate that signal using single-mode fiber. To get such a bright light that can go such a long distance, it’s not unusual to see single-mode fiber used with lasers as the light source. In single-mode fiber, you can see that the core is much narrower, and because of that, there is a single mode of communication that will occur between the source and the destination.