How Fiber Optic Cables Work

Fiber optic cables are crucial for many communications and computing applications. The cables are actually a bundle of minuscule optical fibers that carry light signals, similar to how electrical cables can carry an electrical current. Fiber optic cables are versatile and can be used to carry light around obstacles or around the corner of a room. Optical cables work on the principle of total internal reflection, which keeps the light energy trapped inside the casing of the cable.

How fiber optic cables work: Refraction of light

Fiber optic cables use the phenomenon of total internal reflection to capture and carry the light inside of the cable's casing. When light particles hit a surface that separates two different types of media, they will be absorbed, refracted, or reflected. If light is refracted, the outgoing refraction angle will vary based on the medium's refractive index. If the first medium has a lower refractive index than the second, the light will be refracted to a smaller than normal angle. This commonly occurs when light particles travel from a medium like air to a more refractive medium like glass. Because the refractive angle is less than the incident angle, the light is refracted away from the surface of the second medium.

How fiber optic cables work: Total internal reflection

Total internal reflection happens when the light is traveling from a medium with a high index of refraction to a different medium that has a lower refractive index. Due to Snell's Law, the refracted angle in such a set up must be 90 degrees. If the incident angle is less than 90 degrees, the light cannot be refracted into the second medium. Instead, it will be reflected, causing the principle of total internal reflection. This type of reflection will only happen if the light particles are traveling from a medium with a high refractive index to one with a lower index. It cannot occur when the media are reversed. The chances of total internal reflection increase when the difference between refractive indexes are greater.

How fiber optic cables work: Transfer of data

In fiber optics, this idea of total internal reflection is what keeps the light trapped inside of the cable. The waves of light enter the many optical fibers inside of the casing. Whenever the light hits the edge of the fiber optic cable, it is reflected back inside. With no way to escape, the light eventually travels through the entire length of the fiber optic cable. By using the reflection of light through optical fibers instead of traditional metal wiring, there is less loss of data due to electromagnetic interference.