The demand for reliable and fast data transmission is growing rapidly in areas such as smart homes, Industry 4.0 and cloud computing, pushing the existing network of copper and coaxial cables to their physical limits. Fibre optic cables, on the other hand, can already handle data rates in the terabyte range, which far exceeds the requirements of current home networks and internet connections.
This indicates that fibre optics will replace old copper networks in many countries in the coming years. But how do fibre optic connections differ from conventional copper cables? And how does fibre optic technology actually work?
The Basics of Fibre Optic Technology
Firstly, it is important to distinguish between the terms ‘optical fibre’ and ‘fibre optics’, which are often used interchangeably. Technically, however, there is a subtle difference: ‘optical fibre’ is the generic term for all cables that transmit data via light. ‘Fibre optics’ specifically refers to fibres made of highly pure glass used in telecommunications and for home internet connections. In practice, when we talk about fibre optics for home connections, we are always referring to an optical fibre cable made of glass.
Principle of light transmission: total reflection
At the heart of fibre optic technology lies total internal reflection: when light from an optically denser medium (the core) encounters an optically thinner medium (the cladding), it is fully reflected at a specific angle. This causes the light to ‘bounce’ back and forth within the core without penetrating the cladding, enabling it to be transmitted over long distances with minimal loss. However, this effect only works as long as the angle of incidence is smaller than the critical angle.
Transmission rates and performance
Fibre optics are particularly impressive due to their high transmission rates. In theory, rates of up to 100 Gbit/s and beyond are possible — far higher than copper or coaxial cables can currently achieve. In practice, however, actual speeds depend on several factors.
Signal attenuation over the fibre distance and the quality of the cables and connectors significantly impact performance. Any unclean connector or excessive bending of the fibre can reduce signal strength and thus limit the maximum data rate. Fibre optic networks are generally backward compatible, meaning a connection that supports 10 Gbit/s can often be used with devices requiring 1 Gbit/s. For home networks, this means that if your router, switches and end devices support higher rates, you can upgrade your connection without laying new fibre optic cables.
Structure of a fibre optic cable
A fibre optic cable consists of several layers, each of which performs a specific function:- Core:
The core is the central component of the optical fibre. Light signals are transmitted along the entire length of the cable within this core. This part of the cable consists of particularly pure glass. Alternatively, it can be made of plastic with a higher refractive index than the surrounding cladding. - Cladding:
The cladding glass surrounds the core and is made of an optically transparent dielectric material with a lower refractive index. This layer ensures that the light remains in the core and does not ‘escape’. - Coating und Buffering:
To protect the sensitive optical fibres from mechanical influences, they are coated in a thin layer of plastic. An additional protective layer (buffering) can be applied on top of this. This layer protects against moisture, temperature, and bending stresses, ensuring that the fibres remain undamaged during installation and movement within the cable sheath.
Important to note: Plastic optical fibres (POF) have a significantly larger diameter than glass fibres, at around 0.1 mm. They are flexible and easy to handle, but more sensitive and have higher attenuation values. They are therefore particularly suitable for short distances or indoor applications, such as in vehicles or for industrial automation.
Single-mode vs. multi-mode
In fibre optic cables, the term ‘mode’ describes the number of different paths that a signal can take within the fibre. There are essentially two types:
- Single-mode fibres (SMF): These have a core diameter of around 9 µm and transmit light in a single mode only. This results in minimal differences in propagation time between light waves, making them ideal for long distances (up to several kilometres) and high data rates. Typical wavelengths are 1310 nm and 1550 nm.
- Multi-mode fibres (MMF): With a larger core diameter of 50 or 62.5 µm, several light modes can be transmitted simultaneously. While this simplifies coupling with inexpensive light sources (LEDs and VCSELs), it does lead to slight signal delays between the light paths. Multimode fibres are therefore suitable for short distances, such as within buildings, data centres, and home networks. The typical wavelengths are 850 and 1300 nm.
The most important types of cable for domestic use
There are various types of cable for use with fibre optics in the home. These differ in terms of their structure, material, and area of application. The right cable should be chosen based on where it will be used and what is needed. Indoor cables, for example, are specially designed for use in buildings; they are fire-rated, lightweight and flexible. Outdoor cables, on the other hand, have a tough sheath that is resistant to UV rays and moisture, and are used from the street connection to the building or between houses.Home networks usually use ready-to-install fibre optic cables (patch cables) with connectors such as LC/LC or SC/LC. Depending on their construction, cables can be categorised as simplex (one fibre), duplex (two fibres), breakout or mini breakout – the latter are particularly space-efficient and easy to handle.
Fibre optic cables can be assembled yourself or purchased ready-made. When assembling them yourself, field connectors are attached directly to the fibre. However, this requires experience, specialised tools, and a clean working environment. Pre-assembled plug-and-play cables offer clear advantages: they are ready for immediate use and minimise the risk of installation errors.
Types of connector and their areas of application
Fibre optic connectors are used to reliably connect fibre optic cables to network devices, ONTs or patch panels. They are crucial for stable signal transmission, as even the slightest amount of dirt or incorrect seating can severely impair performance.
The most common types of connector are:
- LC connectors: These are most commonly used in residential applications because they are compact, easy to install, and ideal for patch cables or ONTs. LC connectors are often installed in pairs as a duplex solution, with one fibre transmitting and the other receiving.
- SC connectors: These are slightly larger and more robust than LC connectors. They are used in buildings and data centres. They are easy to plug in and provide a stable connection, but their size makes them less suitable for tight installation areas.
- ST connectors (Straight Tip): These have a bayonet locking mechanism. They were previously widely used in industrial and campus networks. They provide a reliable connection but require a little more space, and are increasingly being replaced by LC connectors in modern home networks.
- E2000 connectors: They have a protective cap and are precision-polished. They offer extremely low reflections and attenuation, and are often used in single-mode backbones or professional fibre optic networks. They are less common in home networks.
- APC connectors (Angled Physical Contact): Have a slightly bevelled contact surface. This angled polish reduces reflections in the light signal and ensures particularly low loss. APC connectors are mainly used with single-mode fibres for connections over longer distances or at higher data rates, for example.
Common sources of error and tips for avoiding them
Careful installation is crucial when working with fibre optics. Common problems arise from excessive bending radii, dirty connectors, or mechanical stress on the cables. Fibre optics can only be bent to the specified minimum radius (usually around 30 mm), as excessive bending causes signal loss.It is also important to keep the connectors clean at all times, as even the smallest dust particles or fingerprints can impair light transmission. Protective caps and suitable cleaning tools are therefore essential. Tensile forces must also be avoided at all costs: fibre optic cables must not be under tension and should be laid loosely with suitable strain reliefs.
How to get started with fibre optic technology
Switching to fibre optics is a step towards faster internet and an investment in the digital future. Those who familiarise themselves with the technology today can enjoy stable, high bandwidths in the long term, as well as laying the foundation for a future-proof home network that can cope with upcoming technologies and increasing data requirements, such as 4K streaming and smart homes.
Glasfaseranschluss im Haus – der typische Aufbau
Ein moderner Glasfaseranschluss beginnt am Hausanschlusskasten (APL), wo ein Techniker das Glasfaserkabel von außen ins Haus führt und fachgerecht terminiert. Vom APL gelangt das Signal zum Optical Network Terminal (ONT) , dem Herzstück des Hausanschlusses. Das ONT wandelt die Lichtsignale der Glasfaser in elektrische Daten um und stellt die Schnittstelle zu Router, Telefon und TV her. Manche ONTs verfügen über integriertes WLAN oder zusätzliche Netzwerkports, um das Heimnetz flexibel zu gestalten.
Careful planning is required when laying fibre optic cable in the house. Empty conduits, cable ducts or ceiling and floor routes are usually used to guide the cable safely to the end devices. Wall bushings protect the sensitive fibre from kinking. The specified bending radius must also be observed to avoid signal loss. As plastic and glass fibre optic cables are sensitive, professional handling is crucial, particularly when installing them in narrow conduits or over long distances.
After the ONT, the connection to the router, switch or end devices is usually taken over by copper cables (Ethernet/LAN). This combination of fibre optic technology and conventional network connections offers the advantages of high bandwidths and interference-free transmission, as well as flexibility.
Glossary – Important terms relating to fibre optic cables and fibre optic connections
| APL (Access Point Line Technology) | The point at which fibre optic cables enter a building; usually installed in the basement. This is where the internal fibre optic cabling begins. |
| ONT (Optical Network Termination) | A network termination device that converts the optical signal from the fibre optic cable into an electrical network signal (Ethernet). It is often connected between the APL and the router. |
| LWL (fibre optic cable) | An umbrella term for cables that transmit data using light signals. They offer extremely high bandwidths with low attenuation and electromagnetic insensitivity. |
| Single-mode fibre (SMF) | Fibre optic cable with a very small core diameter (approx. 9 µm) that conducts light in only one mode. It is ideal for high data rates and long distances (typical in FTTH expansion). |
| Multi-mode fibre (MMF) | Glass fibre with a larger core (50 or 62.5 µm) that transmits multiple light modes. Suitable for shorter distances (e.g. within buildings). |
| Simplex / Duplex | Simplex: one fibre core for data transmission in one direction Duplex: two fibres – one for sending and one for receiving (standard in home networks) |
| Patch cable (fibre optic patch cable) | A patch cable is a pre-assembled fibre optic cable with connectors at both ends. Used to connect devices or ports. Available in various lengths, colours, and connector types. |
| SC connector (Subscriber Connector) | Common fibre optic connector, especially for FTTH connections. It is rectangular with a push/pull mechanism. Robust and easy to handle. |
| LC connector (Lucent Connector) | The LC connector (Lucent Connector) is a compact fibre optic connector that is often used in modern network devices (e.g. SFP modules). It is half the size of an SC connector, making it ideal for dense installations. |
| SFP / SFP+ module | This is a transceiver module that plugs into a router, switch or media converter. It supports various transmission standards (1 Gbit/s and 10 Gbit/s) via a fibre optic cable. |
| Attenuation | Signal loss in the fibre optic cable, measured in dB. This is affected by cable length, connectors and bending radii. The lower the attenuation, the better. |
| Bending radius | The smallest radius at which an optical fibre cable can be bent without degrading the signal. Bending the cable too tightly can lead to excessive attenuation or cable breakage. |
| Field connectors | Fibre optic connectors that can be mounted on a fibre optic cable on site. They are useful for individual installations, but are prone to errors and are costly. |
| Splicing | The professional connection of two fibres with minimal attenuation, usually involving a splicing device, e.g. in commercial construction. |
| Light wavelength | This indicates the wavelength of light (typically 1310 or 1550 nm) with which a fibre optic cable operates. This depends on the cable type (SM/MM) and the transceiver used. |
| Breakout cable | Fibre optic cable with several individually offset fibres. It is suitable for directly connecting several devices or ports at a single point. |
Images: Adobe Stock, reichelt elektronik
