Fiber Optics: How Glass Connects Us All
Every video call, text, and search you make travels as light through strands of glass thinner than a hair. This hidden network of optical fibers spans oceans and cities, moving your data at incredible speed with nothing but light pulses and a clever trick of physics. Here's how it actually works.
The Core Physics
Light travels through different mediums at varying speeds. It may be faster in air and slower through glass. This is why light refracts. Each material has a refractive index: a ratio of the speed of light in a vacuum to the speed of light in the medium. The greater the difference between two materials' refractive indices, the more sharply light bends when passing between them.
When light travels from a denser medium (higher refractive index) toward a less dense one (lower refractive index) and the angle of incidence is greater than a specific value, the light no longer passes through. Instead, it completely reflects back inside the denser medium. This angle is a material's critical angle, and this phenomenon is called total internal reflection (TIR).
Inside Optical Fibers
Fiber optic cables generally have five layers to them: core, cladding, coating, strengthening fibers, and a jacket. The core is a thin and fragile length of glass through which light carries information. It is made up of ultra-pure SiO₂, and the glass is so transparent that looking through several kilometers of it would appear about as clear as looking through a household window. The cladding is a similar piece of glass that differs from the core in its refractive index: cladding generally has a lower refractive index than the core, with a difference of about 1%. This difference is what makes total internal reflection possible, keeping the light trapped inside the core. A very thin acrylate coating covers both components, preventing any scratches or breaks. A strengthening fiber (Kevlar) is then wrapped around the cable to make it durable. Finally, a jacket covers everything. The jacket is made of strong plastics to prevent any damage due to external factors like rain and dirt.
How Does Light Carry Data?
Any data you send over a network can be converted to digital binary (1s and 0s). If you were to upload/download a super large file, it would take a very long time to completely process the file. As a result, everyone else on the network would also find it difficult to request or send data. So, the computer splits the data into tiny packets. Each packet gets labelled with a sender & receiver address and a sequence number. In your home network, you may have a modem connected to a fiber optic cable. This modem is also called an ONU (Optical Network Unit) or an ONT (Optical Network Terminal). Your computer sends the data packets with binary code to the modem; the modem then reads through the packet and sends pulses of light down the optical fiber connected to your home. In its simplest form, a pulse of light signifies a 1 and darkness signifies a 0. As the packets of data travel, they pass through devices called routers, which direct the data toward its destination along the most efficient path available. Once they reach their destination, a receiving computer reads the address and the sequence number on each packet to reassemble the data for the receiver. Finally, the computer converts the 1s and 0s back into sensible data for the end-user.
How Fiber Optics Connects the World
Today, over 95% of the world's international internet traffic travels through subsea optical fibers: the cables are simply arranged on the seabed, allowing transoceanic communication to take place. Fiber optic cables can also be set up on land by burying cables underground and below cities. Much of this fiber ultimately leads to cell towers, which transmit the final "last mile" of data wirelessly using radio waves. Fiber optic technology has become the standard in today's networks thanks to its extremely fast, high-capacity transfer of data.
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