Fiber

Similar to some sort of conductor that conducts electricity, where we can turn it on and off and send data down a line, we can do the same thing with light. We can turn a light on and off to represent different information. In the very crude sense, we could have a flashlight that sends data, with some sort of sensor that picks up that light information and turns it into some sort of data.

Now, the problem is that a flashlight really disperses the data, so we need to somehow focus it. That's where lasers come in, where a laser is a focused light and so it will travel much longer distances. There's different ways that we can create this laser light. But then the other issue is how do we go around corners, and how do we get the data past walls and to other areas. That's where fiber optics comes in.

How fiber routes light

Fiber optics allows us to route the light in certain directions. What it does is it uses some physics principles of how light, as it travels through transparent but more dense material, will actually do some refraction of that material. It's a similar concept to when you look at a glass of water and how it will bend the light. It uses some of those same characteristics.

This is a fiber optics cable that I have right here, and you see in the middle of it I have a material that's transparent but dense. That would be either glass or some sort of plastic that we have running through there. The higher-end ones are actually glass, because it has less attenuation and it will disrupt that fiber light less than plastic. Plastic tends to be a little more cloudy and will interrupt that light a little more. So that light gets refracted and bounced off as it goes down this really fine piece of fiber, this fiberglass.

Now the thing is that it's very breakable. This piece of fiber, if you bend it too much, can actually break, because it's actually glass inside of it — or even if it's plastic, then the plastic can break also. So it's fragile. It has multiple sheathing around the outside to protect it. Try not to bend it too much, and when you handle it you still have to be somewhat careful with it. If you have any kind of connection issue, it could be because the piece of glass is broke.

But we can take this and we can shine a laser in one side, and it will refract off the edges and bounce around in there and bounce out the other side, and then we read that light, whether it's on or off. We can get really fast connection speeds because that light is really quick. It actually turns on and off at the speed of light. So we can continually improve and make fiber optics go faster and faster.

Advantages over copper

There's a lot of advantages of fiber optics over some other choices. First of all, similar to a copper line, it is a direct connection from one point to another. Because of that, because it's not wireless, it tends to be more stable once you make that connection. As long as there's no breaks in the line, it tends to be a very stable connection.

What makes it better than copper is that it's less susceptible to attenuation. Where copper, over time, adds resistance to it and then the signal degrades, the same or a similar effect happens with fiber optics — light will degrade over time as it hits this material or goes through this material. However, it's less susceptible to that attenuation, so it can go a longer distance. Really, one of the powerful things with this is that it can go longer distances.

In fact, sometimes we relate fiber optics to speed, which isn't really — fiber optics is really not faster than copper, because sitting on both sides is electrical pulses. It's just that we can go longer distances without that attenuation, and so we can achieve higher speeds at longer distances, and that's why we think of fiber as being a really fast media.

The other thing that it has a step up above copper is that it's not susceptible to electromagnetic interference at all. It's light, and so it doesn't get interfered with by all of these EMI or EMF around. It doesn't have crosstalk, and so it's very stable from that perspective. It's a step above copper in many ways.

Disadvantages

However, there are some disadvantages, otherwise we'd be using it everywhere. The main disadvantage is just expense. It can be costly, because the fiber is expensive to make and it's really fragile, so you have to protect it. It also can be more difficult to actually install, because there's tighter constraints with it on how far it can bend. So there are some disadvantages to fiber optics as well.

Where fiber is used

We typically don't see a lot of companies that are installing fiber to the desktop. There is not a strong use case for that because of the expense of it. So where do we use fiber?

There's a lot of times we'll use fiber to go that last mile to the home, so there's fiber to the home, or FTTH. We've got the long-haul networks that set up those long-haul networks, or over the ocean floor. There's some areas like that where we like to have this fast speed and longer distances.

So those long hauls, but within our LANs we like to use them as well. There's a couple of places that we really like to use fiber. One is between our switches. You see that this switch right here has regular Ethernet ports on it that are copper based. It's got those connectors in it where you slide in those SFPs. You slide those in there, and then these are the fiber connections, and the fiber connections then can make the link between the switches. Quite often those come back to a main switch that connects all of the switches together. This would be very similar to what a lot of people will use as the core switch, and then you have fiber that's running from the core out to all of the individual access switches. So there's definitely use cases for using fiber, and you'll definitely see it in a lot of networks out there.

Multimode versus single mode

Here I've got an example of a multimode fiber optics cable and a single mode. A multimode is 50 microns thick — that's the diameter of that fiber inside of the cable — and the single mode is 9 microns, so quite a bit smaller. Functionally it's quite a bit different. Just as an example of that, the human hair is 70 micron, so we're talking about pretty small here. These are really small connectors.

But the difference between the 50 microns and the nine microns produces a fairly large result. That is, when light is transmitted through this single mode, it bounces back and forth through this and then comes out the other side, and the result of that is that you get a little more attenuation with that. Versus the nine micron allows it to take a much straighter path through this piece of fiber, and it doesn't bounce around in there like it does with the multimode. Therefore it takes a much more direct path, has less attenuation, can go longer distances, and so you're able to get a much clearer signal through it.

That's the difference between multimode and single mode. A lot of places find that multimode works just fine. We see single mode — once again, as technology develops, things become cheaper, and the expense ratio between these two is probably not as big as it used to be. So we may see some transitions.