EMZETT.Fibre
In short: Fibre-optic cable — transmits data as pulses of light instead of electrical signals, enabling very high bandwidths over long distances.
In more detail: Because light is transmitted instead of electricity, fibre is immune to electromagnetic interference and hardly loses any signal quality over long distances — unlike copper cables. Used both over long distances (backbone networks) and increasingly all the way to the end customer (FTTH, “fibre to the home”).
In Depth
Physical principle: total internal reflection
An optical fibre consists of a thin glass core surrounded by a cladding with a lower refractive index — light fed into the core is therefore trapped inside by physical total internal reflection as soon as it hits the boundary at a shallow angle, and “travels” through the fibre practically without loss, even over many kilometres and around gentle bends. There are two main types: multimode fibres (thicker core, several light paths/“modes” possible at once, cheaper, suitable for short distances such as data centre cabling) and single-mode fibres (very thin core, only a single, exactly straight light path possible, more expensive in the laser optics required, but practically without alternative for very long distances such as intercontinental submarine cables, because with multimode the different light paths take different amounts of time over long distances and the signal would blur — modal dispersion).
Advantages over copper
Compared with copper cables (coax, twisted-pair cables), fibre has three decisive advantages: practically no signal attenuation over long distances (depending on the cable type, copper needs active amplifiers/repeaters every few hundred metres, while high-quality single-mode fibre manages entirely without them over tens to more than a hundred kilometres), complete immunity to electromagnetic interference (because no electrical signal at all, only pure light, is transmitted — fibre can be laid right next to high-voltage lines without problems, which would cause interference with copper cables), and a considerably higher maximum bandwidth — modern fibre technology with wavelength-division multiplexing (several colours of light at once over the same fibre) transmits terabits per second over a single physical fibre.
Drawbacks and installation
The drawback: fibre is more sensitive to mechanical stress (sharp kinking can break the fibre permanently without this being visible from the outside), and installation or repair requires specialised tools — in particular fusion splicers, which melt two fibre ends together precisely under controlled heat instead of simply connecting them mechanically as with copper. This tends to make fibre installation and maintenance more expensive and complex than more robust copper cabling, which is outweighed by the considerably higher capacity and range as soon as these are really needed.
FTTH vs. FTTC for end customers
For end customers, a distinction is made depending on how close to the household the fibre is actually brought: FTTH (“fibre to the home”, fibre right into the flat — the fastest and most future-proof variant, because no copper section limits the speed anywhere along the route) versus FTTC (“fibre to the curb/cabinet”, fibre only as far as the distribution box at the roadside, with the last metres to the house still running over classic copper, often over coaxial cable via DOCSIS or DSL) — a compromise that is faster and cheaper to roll out, but limits the achievable end speed through the remaining copper section.
See also: Coax, Bandwidth, Cat categories and specifications