EMZETT.Fiber optics (FTTH): Internet over light
In short: With fiber connections, data is transmitted as pulses of light through thin glass fibers right into the house, at very high speed and range.
In more detail: Instead of electrical signals on copper cables, a glass fiber carries light pulses. The light is guided inside the fiber by total internal reflection. There is hardly any attenuation, hardly any interference from electromagnetic fields, and the range without amplifiers is many kilometres. FTTH (fiber to the home) brings the fiber into the home; with FTTC (fiber to the curb) it ends at the street cabinet and the rest runs over copper (VDSL).
In Depth
Structure of a fiber
The core (a few micrometres to 50 µm) conducts the light, the cladding with a different refractive index keeps it in the core by total internal reflection, and a coating protects the outside. Single-mode fibers (core about 9 µm) carry a light signal over very long distances and are used in telecom networks and house connections. Multimode fibers (50 or 62.5 µm) suit shorter distances, for example in the data center.
Technology in the house connection
Usually GPON (Gigabit Passive Optical Network) or a successor (XGS-PON) is used: one fiber from the distribution point is split by passive splitters to many households. In the house it ends in the fiber modem (ONT), which converts light to Ethernet. Your router connects to the ONT. Alternatively there are point-to-point connections with a fiber of their own per household.
Advantages
- High bandwidth (1 Gbit/s and more, often symmetrical, i.e. equally fast on upload).
- Low and stable latency.
- No dependence on line length, unlike DSL.
- Future-proof, since only the devices at the ends need to be replaced. For links between data centers and across oceans (submarine cables) it is indispensable anyway.
In practice
Laying is laborious, so availability differs regionally. The fiber is sensitive to tight bends, so do not bend cables sharply. Connectors (SC, LC) and plugs must be clean; dirt on the end face degrades the signal. The light is invisible (infrared) and can damage eyes: never look into open fibers or ports.