Fiber forms the backbone of the internet and company networks today, because it carries an enormous amount of data over long distances without interference. Behind terms like single mode, multimode, WDM or GPON lies quite an understandable logic. Let us explain how fiber works and what types exist.

How fiber works

An optical fiber is a thin glass strand that carries data with light, not electricity. A transmitter (a laser or LED) at one end sends light pulses, which travel through the fiber to the other end, where a receiver reads them back into data. Because it is light in glass, fiber is not affected by electrical interference, handles enormous speeds and carries the signal far further than a metallic cable. That is why it is used wherever a lot of data and long reach are needed.

Single mode versus multimode

This is the basic division of optical fibers, and they differ in core thickness and reach:

  • Multimode has a thicker core (usually 50 micrometers), in which light travels along several paths at once. It uses cheaper transmitters and suits shorter distances on the order of hundreds of meters, typically within a building or a data center. It is marked OM3, OM4 or OM5 and tends to be orange or aqua.
  • Single mode has a very thin core (around 9 micrometers), in which light travels a single straight path. It uses a precise laser and handles enormous distances, kilometers to tens of kilometers. It is marked OS1 or OS2, tends to be yellow and is used by operators for long routes and fiber to the home.

Simply put: multimode is cheaper for short runs in a building, single mode is for long routes between cities and to customers.

WDM: several signals in one fiber

A single fiber can carry far more than it might seem, thanks to WDM (wavelength division multiplexing). The principle is simple: several signals are sent down the fiber at once, each on a different wavelength, that is, put simply, a different color of light. The receiver separates them again at the end. This multiplies the fiber’s capacity without having to dig new routes. We distinguish simpler CWDM with a few channels and dense DWDM with tens of channels for operators.

GPON: how fiber reaches your home

When you have a fiber connection at home, it is almost certainly the GPON (passive optical network) technology. It works so that a fiber runs from one device at the operator to a passive splitter, which divides it among several households. At your home it ends in a small box (the ONT), to which the router connects. So part of the fiber is shared among neighbors, but the capacity of fiber is so large that you do not notice it in practice. Passive means there are no active elements on the route that would need power, which is cheap and reliable.

Connectors and the fragility of fiber

Fiber is terminated with connectors, most often the SC type (square) or LC (smaller). The glass fiber is fragile and sensitive: it must not be bent too much, the face of the connector must be clean and dust-free, otherwise the signal drops significantly. A green connector marks a so-called APC termination with better reflection, which does not mix with the ordinary UPC. That is why it is better to have fiber connected and fusion-spliced by a professional.

Where fiber makes sense

  • Long routes and links between buildings, where metallic cable is not enough.
  • Noisy environments with electrical interference, where metallic cable would pick up noise.
  • The network backbone and high speeds in companies and data centers.

For short runs in a house or office, quality metallic cabling is often enough, which we cover separately.

Planning fiber for your company or a link between buildings? Get in touch, we will design and deliver a tailored solution, also as part of IT support for companies.