Total Internal Reflection 101

Total internal reflection is a scientific phenomenon critical in fiber optics. Since we think the mechanics are fascinating, we thought it would be useful to pose a scenario that helps better explain what makes optical fiber work.

Read on, then get in touch and we’ll take care of all of your network infrastructure consulting needs in Mercer County, NJ:

Say you’re scuba diving with a laser. Why you would ever be doing that is beyond us, but for the sake of this example just pretend there’d be a scenario in which you’d have a laser underwater. How you possessed the laser to begin with is questionable, but we won’t ask too many questions.

Anyway, so you’re swimming along with your laser, and you get the bright idea of shining it. The angle at which it points in relation to the surface is very important, and will dictate a number of outcomes for how its light will behave.

In order to understand total internal reflection, first you should know the difference between two key words. Let’s brush up on our physics terminology:


If the laser light hits the surface of the water and bounces out and into the air above, that light is refracting, because it’s leaving the initial area of containment—in our example, that’s the ocean. Here’s a basic example using a glass of water and a straw. In this case, the straw replaces your laser light.

As you can see, “light” (the straw) is hitting the surface at an angle which makes it refract out of the cup. That brings us to our next term.


When the laser light hits the surface and bounces back into the water, it is reflecting back into our area of containment. Here’s an example of light reflecting in a glass tank, rather than refracting out of it.

When your light hits the water’s edge at an angle that makes it shoot right along the surface, you have reached your critical angle, which is depicted below.

Now, say the ocean floor around where you’re scuba diving is actually a mirror with the capacity to refract laser light, just the same way the surface could. When you shine your light toward the surface at an angle that allows it to reflect back into the water, shine down toward that reflective ocean floor, hit it, reflect back into the water again, and repeat that process infinitely, causing the light to be totally contained in the water, you have caused (drumroll, please) total internal reflection. Here’s a simple video showing the phenomenon:

Hurray, you did it!

Fiber optic cables use totally reflective light to transmit information from one end to the other, very quickly.

So, if you need optical fiber, voice and data cabling for your Monmouth County, NJ business, or a variety of other telecom services, give us a call today and we’ll get you set up. We promise not to work in scuba gear!