So in the last video we looked at how we could send in some information over a copper wire. In this video I want to look at a couple other common media that we might use in networking. And one of them, a very common one, is fiber optics. And so this is a fiber optic patch cable that has two different strands, the blue and the red.
It's just sort of part of one cable. But the way this works is that each of these strands has a fiber strand here. fiber strand in the middle and then outside there's this The the fiber strand is basically this really thin strand of glass that has a coating of a different glass which is called cladding and the cladding is slightly different refractive index from the fiber strand and so what happens is if you send light in usually with a laser into this strand the The difference in refractive index between the cladding and the strand itself is enough that will cause total internal reflection here, where the fiber light will refract off of the edge here.
And so as this fiber travels through this fiber, or excuse me, as the laser light travels through this fiber, it refracts off of this difference in refractive index and will even sort of refract around corners. And so you can have this cable coiled up like this. and the light will continue to refract through and then come out the other end. And so here's an example here where there is a laser attached on this end shooting some red light into the blue fiber here.
And you can see over here how you can see the red light visibly here coming out. Sometimes in networking they'll use infrared light, but it's the same concept. And you can see, again, the light sort of reflecting off the table here.
And so it's very clear you can see this one does not have light and this one does. And so going back to our previous discussion about encoding different symbols, you can imagine one symbol that we might encode is light is off. Another symbol that we might encode is the light is on. And you could use this to send information by pulsing the light on or off. And that's a very basic way of sort of on-off keying to send information through fiber.
Another way that we could send information that is also very common in networks is Using radio waves and so this is an example of a wireless router of some sort and there's an antenna here and Very very roughly the way this works is you have this antenna which is just essentially this sort of wire It might be a coil of wire or something like this But the way it works is you vary the voltage so this this device here is varying the voltage in that in that antenna at a high frequency, so this might be a 2.4 gigahertz sine wave that this voltage is being is fluctuating at. And then by doing that this antenna will then radiate radio waves which is just sort of basically how an antenna works. And then another device might pick up those radio waves and then be able to amplify them and convert them back into the same the same signal. And so what we could do here is this might be a 2.4 gigahertz sine wave And then what we could do is we could shift the phase of this a little bit, so that instead of, so for example, instead of the phase of the sine wave, if we kind of zoom in looking like this, we could shift it so the phase maybe goes like this, which basically just sort of inverts it.
And this is a way that we can use to alter a radio wave in a way that we can detect on the other end. And so if this is sort of the in-phase, signal, we could have an out-of-phase signal or a 180 degree out-of-phase signal that represents a different symbol. And so, you know, this in-phase might represent a zero and this out-of-phase might represent a one. And by shifting the phase between this and this very rapidly, we might be able to send ones and zeros across radio waves. And so these are just a couple different ways that we can use to send symbols over fiber or over radio waves.