How Photons Become Facebook: Data transmission through fiber optic cables

by admin-natalie | Dec 22, 2017 | Uncategorized

Picture this: It’s been a long day at work. You come home and all you want is something to take the edge off, something cute. We’ve all been there. That’s the moment you log into Facebook, and start scrolling.

But how did your fiber Internet deliver that feed? How does a photon stream carry data across tens, hundreds or even thousands of miles of fiber optic cable? How does light carry data at all? Light isn’t, in itself, network information—but the properties of photons make them excellent candidates for data transmission. Read more on why life’s better in the light.

There’s a lot going on here. That’s why today we’re setting out to answer these questions and more.

How Fiber Optic Cables Work

So what’s going on inside a fiber optic cable anyway? It’s easy to understand that laser light enters one end of the cable and exits the other in a flash. We see this property working in surgeons’ endoscopes and at the nettle-ends of our color-changing fiber optic Christmas trees—but how?

It’s possible because fiber optic cables achieve what’s called total internal reflection, which occurs when two or more media and their refractive indices affect the way light propagates in significant ways. We won’t get too intertextual with this term, but the basic idea is this: the hair-thin glass core through which the light travels is more reflective than the protective glass cladding that surrounds it, and so the light signal naturally “wants” to “bounce” repeatedly and continuously, for as long as it’s able, down the glassene superhighway as opposed to getting bogged down by the other, less reflective parts of the cable core. We mean, wouldn’t you? In another way, you might consider it romantically: Light loves going fast—that’s exactly why we chose it to be what gets your data where it needs to go.

 


All that ricocheting reflection and refraction, all-said, comes at a marginal cost. Because fiber optic cables’ glass tubing isn’t a perfect vacuum, each miniscule bounce takes its micro-toll on the signal. Don’t worry, though. When things start slowing down, about every 50 mi (80 km) or so, the signal stream is re-amplified inside of strategically-placed nodes called “repeaters.” This node-to-node distance, which varies with the types of fiber technology emplaced, is farther than what can be achieved by copper cable by nearly a factor of twenty. If twenty-times seems like a lot, it is—at NebraskaLink, we’re all about infrastructural economy, and it’s fiber optics itself that allows us that freedom from excess.

But what exactly is that signal?

In short: The data’s in the difference.

 

Conversion Factors

What we do when we convert light into data (and vice-versa) is something called pulse code modulation. Because light travels in waves, we’re able to use extremely sensitive instruments to measure even the most subtle and infinitesimal changes in wavelength, or the peaks and troughs of these waves’ curves. When taken in aggregate, these differences in wavelength become a sort of reference key. It’s kind of like how the “long-short, short’s” of Morse code represent letters of the English alphabet. By assigning each step of a signal’s sine wave to a three, four, or six-digit bit value (as seen in the diagram) we’re able to make a sort of language out of all the noise.

 


This “assigning” work is done by what we call modulators and demodulators. A modulator takes in the electronic signal from, say, your desktop computer’s ethernet port and transposes it into a fiber optic cable-ready photonic (light) signal. When that packeted information reaches its destination, the demodulator waiting for it administers the inverse treatment, and it’s back to digital again. In fact, this process—called modulation-demodulation—is exactly where we get a word that we’re sure you’re familiar with: modem!

 

Blazing the Trail from A to B

Now that we’ve laid everything in place, let’s map it out.

 

 
 
1. First, while scrolling your Facebook feed you spy a post your aunt made this afternoon—she’s created a new album filled to the brim with her favorite photos of kittens in boxes. Being a reasonable, red-blooded human being:  (1) You click.

2. This click creates a request (we’ll call it “Kittens, please!”) from your computer all the way to Facebook’s servers.

3. The request begins as digital information which (2) moves from your desktop to your modem, where it’s (3) modulated into a photonic signal.

4. From there, (4) it’s off to the races—the signal hits repeater after repeater, enjoying breakneck boosts in strength and speed along the way.

5. Once it reaches the nearest Facebook server space, your request is (5) demodulated, interpreted and received.

6. Facebook hears “Kittens, please!” and readily obliges. It packets all those kitten photos, and the entire process, 1→5, begins again in reverse (1←5).

Before you can even blink, your web browser receives and downloads Facebook’s packet, uses it to build and render a new page, and the album opens right up. Thanks to NebraskaLink (and your aunt) your evening gets a whole lot cuter.

Now, you might be wondering whether there are exceptions to these rules especially if you’re in the networking-know (“But what about delta modulation?”). There are too many exclusions, exceptions, and special conditions to name in this one single post when it comes to making fiber optic Internet work, but that’s what fiber optic data transmission is—a perfect storm. Fiber optic internet is only possible because the right components come together under exact elements at a precise moment in time. We at NebraskaLink like to think our company, our network and our unbeatable service operate very much the same way.

To see it for yourself, or to find out more, give us a call. Like a kitten guarding the packing peanuts inside their favorite box—we’re always standing by.