Network Fibre Optics: How Modern Optical Networks Work

Introduction to Network Fibre Optics

Network fibre optics forms the backbone of modern internet, cloud computing, and telecommunications infrastructure across the UK and globally. Since widespread commercial deployments began in the late 1980s and accelerated through the 1990s, optical fibre networks have expanded to connect homes, businesses, data centres, and entire continents. Today, data is transmitted as light pulses through ultra thin strands of highly transparent glass, bundled into fibre optic cables laid under streets, across cities, and on the seabed between continents.

This article answers two fundamental questions: what is network fibre optics, and how does it actually work? We’ll move from basic principles into cable types, network architectures including FTTx, metro, and long-haul designs, then examine the business advantages and disadvantages before looking at future trends. The practical relevance is clear: from gigabit fibre broadband services now available in UK cities like London, Manchester, and Edinburgh, to dark fibre lines linking data centres across London, Dublin, Amsterdam, and New York.

Consider the transatlantic cables deployed after 2010 to support explosive growth in streaming and cloud services. Google’s Dunant cable, completed in 2020, achieves approximately 250 Tbps using advanced modulation techniques across the Atlantic Ocean. Meanwhile, UK operators have rolled out full-fibre connections reaching millions of premises, with coverage expanding rapidly each year. These networks carry everything from Netflix streams to international financial transactions, demonstrating how fibre optic technology has become essential infrastructure.

What Is Network Fibre Optics?

Network fibre optics is the use of optical fibre cables to carry digital data traffic—including internet, voice, and video—as light signals across local, metro, and long-haul networks. Unlike traditional copper cables that transmit data as electrical signals, optical fibre uses photons travelling through glass to transmit data at incredible speed with minimal signal loss over long distances.

The basic structure of an optical fibre consists of a transparent glass core surrounded by a cladding layer with a slightly lower refractive index. This core, typically measuring about 9 micrometres in diameter for single mode fibre or 50-62.5 micrometres for multimode fiber, carries the light signals. The cladding reflects light back into the core through a phenomenon called total internal reflection, preventing the signal from escaping. Protective buffer coatings and an outer jacket encase the fibre, while strength members within the cable provide mechanical protection. Multiple fiber optic strands are bundled together into cables suitable for installation in ducts, on poles, or on the seabed.

The scale of modern fibre optic cable capacity is remarkable. A single fibre strand, about 125 micrometres in diameter (comparable to a human hair), can carry multiple 100 Gbps or 400 Gbps wavelengths simultaneously using wavelength-division multiplexing. Cable bundles containing 96, 192, or more fibres can deliver terabits per second of aggregate bandwidth across a single route.

The history of fiber optics spans several decades. Early experimental systems emerged in the 1960s, but practical deployment began when Corning developed low-loss glass fibres in 1970, achieving attenuation below 20 dB/km. Commercial long-haul fibre networks appeared in the late 1970s and 1980s, revolutionising telecommunications. Widespread FTTH and FTTP rollouts followed in the 2000s through 2020s, bringing high speed internet connections directly to homes and businesses.

How Do Fibre Optic Networks Work?

Understanding how a fibre optic network moves data from one point to another requires following the complete signal path. Data starts as electrical signals in networking equipment such as routers or switches. Optical transceivers convert these electrical signals into light signals using lasers (for single-mode) or LEDs (for multimode applications). This light travels through the optical fibre core, bouncing along through total internal reflection, until it reaches the destination. At the receiving end, another transceiver converts the light back into electrical signals for processing.

Total internal reflection is the fundamental principle that makes light transmission through fibre possible. When light travels from the higher-refractive-index core (typically 1.46-1.47 for silica glass) into the lower-refractive-index cladding (around 1.45), any ray exceeding the critical angle is completely reflected back into the core. This allows light to propagate along the fibre for tens of kilometres between optical amplifiers with minimal signal degradation.

The way light travels through fibre depends on whether the fibre is single-mode or multimode. Single mode fibre has a narrow core (8-10 micrometres) that allows only one mode of light to propagate. This eliminates modal dispersion and supports high speed data transmission over distances of 40 km or more without amplification. Single mode is the standard choice for long-haul networks, metro rings, and modern FTTH deployments.

Multimode fiber features a larger core (50-62.5 micrometres) that allows multiple light beams to travel along different paths simultaneously. While this makes coupling light into the fibre easier and reduces transceiver costs, modal dispersion limits the distance and speed achievable. Multimode is typically used for short distances within buildings, campus networks, and data centres, supporting links up to a few hundred metres.

Wavelength-division multiplexing (WDM) and its denser variant, DWDM (dense wavelength-division multiplexing), allow multiple colours of light—each at a different wavelength—to travel through the same fibre simultaneously. Each wavelength carries an independent data channel at 10, 40, 100, or even 400 Gbps. Modern DWDM systems can stack 80 or more wavelengths onto a single fibre, enabling multi-terabit backbone links that have powered internet growth since the mid-2000s.

Key Components in a Network Fibre Optic System

The fiber optic components that make up an optical network perform specific functions at different points in the system:

• Optical fibre – The transmission medium itself, consisting of core, cladding, and protective layers, carrying light signals between locations

• Connectors – LC, SC, ST, and MPO/MTP connectors provide standardised physical connections between fibres, patch panels, and equipment

• Patch panels – High-density termination points in data centres and exchanges where fibres can be cross-connected or routed to equipment

• Optical transceivers – Modules (SFP, SFP+, QSFP28, QSFP-DD) that convert electrical signals to light and vice versa, plugging into switches and routers

• Optical amplifiers (EDFAs) – Erbium-doped fibre amplifiers boost fading optical signals on long-haul routes, enabling spans exceeding 100 km without electrical conversion

• Optical splitters – Passive devices that divide one optical signal to multiple paths, essential in PON architectures serving multiple premises

• Optical switches and ROADMs – Reconfigurable optical add-drop multiplexers allow dynamic wavelength routing in metro and long-haul networks

In a typical deployment, the access network includes Optical Network Terminals (ONTs) at customer premises and Optical Line Terminals (OLTs) at the exchange. Metro rings connect exchanges and data centres within a city at 10G to 400G per wavelength. Long-haul routes link cities and countries using amplified spans and DWDM technology.

Performance characteristics vary by fibre type and equipment. Attenuation in modern single-mode fibre runs approximately 0.2-0.3 dB/km at the common 1550 nm wavelength, with 1310 nm also widely used for shorter reaches. Typical long-haul span lengths range from 60 to 100 km between amplifiers.

Types of Fibre Optic Cables and Optical Fibres

The choice of cable and fibre type determines the distance, speed, and cost characteristics of any fibre optic network deployment. Enterprise networks and carrier backbones select different fibre types based on their specific requirements, from short building links to transoceanic connections.

Single-mode fibre (SMF) uses a 9-micrometre core that permits only one propagation mode, eliminating modal dispersion entirely. Standards including ITU-T G.652D (standard SMF), G.655 (non-zero dispersion-shifted), and G.657 (bend-insensitive) cover different deployment scenarios. Single-mode dominates long-haul networks, metro rings, and FTTH installations, supporting wavelengths from 1 Gbps to 400 Gbps and beyond. The small core requires laser light sources and precise alignment, but delivers superior performance over long distances with very low attenuation.

Multimode fibre (MMF) comes in several grades designated OM1 through OM5. OM1 (62.5-micrometre core) and OM2 (50-micrometre core) are legacy types found in older installations. OM3 and OM4 (both 50-micrometre, laser-optimised) support 10 Gbps to distances of 300 and 400 metres respectively. OM5 extends this to support short-wavelength division multiplexing. Multimode remains common in campus networks, server rooms, and older data centres where distances are short but fibre density is high.

Cable construction varies by environment. Loose-tube outdoor cables protect fibres in gel-filled tubes for duct or aerial installation. Tight-buffer indoor cables place fibres directly in protective coatings for flexibility in risers and plenums. Blown fibre systems allow fibres to be installed into pre-placed microducts. Armoured cables provide steel or aluminium protection for direct burial. Submarine fibre optic cables incorporate power conductors for amplifiers and multiple layers of protection against water pressure, fishing activity, and anchor damage—these undersea cables have connected continents since the 1990s.

Connector types serve different purposes across the network. LC connectors dominate high-density data centre patching due to their small form factor. SC connectors remain common in telecom environments. ST connectors, with their bayonet coupling, appear in older installations. MPO/MTP multi-fibre connectors support 12 or 24 fibres in a single connection, enabling rapid deployment of high-speed links in modern data centres.

Optical Fibre Modes and Performance Characteristics

Modal dispersion occurs when light travels along different paths in multimode fiber, causing signal spreading that limits distance and bitrate. Chromatic dispersion affects all fibre types, as different wavelengths travel at slightly different speeds. Together, these phenomena constrain what any given fibre can achieve.

Key performance values network planners should understand:

• Attenuation at 1550 nm: approximately 0.2 dB/km for modern single-mode fibre

• Attenuation at 1310 nm: approximately 0.35 dB/km for single-mode fibre

• Multimode attenuation: typically 2.5-3.5 dB/km depending on grade

• Single-mode fibre supports spans of 10-80 km or more depending on equipment

Common Ethernet standards over fibre include 1000BASE-LX (1 Gbps, up to 10 km on single-mode), 10GBASE-LR (10 Gbps, up to 10 km on single-mode), and 10GBASE-SR (10 Gbps, up to 300 metres on OM3 multimode). Higher speeds use 40GBASE-SR4 (40 Gbps over 100-150 metres on OM3/OM4) and 100GBASE-LR4 (100 Gbps over 10 km on single-mode).

Optical Network Architectures (FTTx, Metro, Long-Haul)

The term “network fibre optics” encompasses vastly different designs depending on whether the network serves residential access, city-wide connectivity, or intercontinental transport. Access networks using FTTx architectures bring fibre to homes and businesses. Metro networks connect sites within cities and regions. Long-haul networks span countries and continents.

FTTx variants describe how close fibre comes to the end user:

• FTTH/FTTP (Fibre to the Home/Premises) – Full fibre from exchange to customer premises, now common in UK new-build estates and increasingly retrofitted in urban areas since around 2015

• FTTC (Fibre to the Cabinet) – Fibre reaches street cabinets, with copper wire completing the last few hundred metres to premises

• FTTB (Fibre to the Building) – Fibre terminates in a multi-tenant building, with internal copper or ethernet distribution to individual units

PON (Passive Optical Network) architectures use optical splitters to share a single fibre among multiple users, typically 32 or 64 premises per fibre. GPON (2.5 Gbps downstream) became widespread in the 2010s, while XGS-PON (10 Gbps symmetric) now enables symmetric gigabit services. Point-to-point Ethernet fibre provides dedicated fibres to each user, offering more bandwidth but at higher cost per connection.

Metro fibre networks connect exchanges, data centres, and major business sites within a city or region. Ring or mesh topologies provide resilience, with traffic rerouting automatically if a fibre cut occurs. Modern metro networks operate at 10G to 400G per wavelength, with DWDM enabling multiple wavelengths per fibre pair.

Long-haul and submarine networks carry data between cities, countries, and continents. Amplified spans of 60-100 km use EDFAs to boost signals without converting to electrical. DWDM systems carry signals over many thousands of kilometres. Major transatlantic systems deployed after 2010 support cloud providers and content delivery networks, with capacities reaching hundreds of terabits per second.

Dark Fibre vs Lit Fibre in Network Design

Dark fibre refers to unused physical fibre pairs leased to organisations that provide their own optical equipment. The customer controls wavelengths, speeds, and protocols, gaining maximum flexibility. Large enterprises, carriers, and hyperscale operators commonly use dark fibre for interconnecting data centres and building private backbone networks.

Lit fibre means the service provider supplies a managed bandwidth service—typically 1 Gbps, 10 Gbps, or 100 Gbps Ethernet—rather than raw fibre. The provider handles optical equipment, monitoring, and maintenance. This approach suits organisations that need high bandwidth connectivity without the expertise or capital to run their own optical network.

Dark fibre offers significant advantages for organisations with the technical capability to exploit it: complete control over capacity, the ability to upgrade speeds by changing equipment, and potentially lower long-term costs at scale. However, it demands upfront capital for optics and ongoing expertise for management. Lit services reduce complexity and suit smaller teams or situations where connectivity needs are straightforward and well-defined by available service tiers.

Applications of Network Fibre Optics

Fibre optic technology underpins everyday activities that billions of people take for granted: streaming HD and 4K video, participating in remote work, using cloud applications, making VoIP calls, playing online games, and collaborating in real time across continents. Video alone now accounts for approximately 80% of internet data traffic, and this volume simply could not travel over legacy copper connections.

Enterprise and data centre use represents a major application area. High-density fibre links in server racks connect thousands of servers in spine-leaf architectures using 10, 25, 40, and 100 Gbps optics. Cross-connects between co-located data centres in cities like London, Frankfurt, and Amsterdam run over dedicated fibre, often dark fibre leased from carriers. These environments demand high bandwidth applications with extremely low latency connections.

Telecom and ISP backbones form the core networks carrying IP, MPLS, and optical transport traffic between major hubs. These networks support mobile (4G and 5G) backhaul and fronthaul, as well as fixed broadband customers. A single failure-resilient fibre route between two cities might carry signals representing millions of simultaneous phone calls, video streams, and data sessions.

Specialised applications include financial trading links requiring ultra-low latency—where every microsecond matters for arbitrage strategies—research networks connecting universities and laboratories with high-capacity dedicated paths, and content delivery networks (CDNs) moving data from origin servers to edge locations closer to end users.

Everyday Services Powered by Fibre

Consumer-visible services that depend on fibre networks include on-demand television platforms that have largely replaced cable television in many households, cloud gaming services that launched after 2019 and stream interactive video in real time, and video conferencing platforms that saw explosive growth from 2020 onward during widespread remote working.

When a home user starts streaming a film, their request travels over local access fibre (perhaps FTTH using GPON) to the nearest exchange. From there, it moves across metro fibre to a regional data centre or internet exchange. If the content isn’t cached locally, the request continues over long-haul fibre—possibly across undersea cables—to a data centre on another continent. The response follows the reverse path, all within tens of milliseconds.

Consider the path of a simple backup job: files leave a home PC, travel over fibre broadband to the ISP, cross metro rings to reach a cloud provider’s data centre, then replicate over long-haul fibre to a geographically distant facility for redundancy. The entire round trip might touch a dozen different fibre links, yet the user experiences only a progress bar advancing steadily. This is the invisible infrastructure that makes high speed connectivity reliable and ubiquitous.

Advantages and Disadvantages of Network Fibre Optics for Business

Fibre is now the preferred medium for new business connectivity deployments, replacing legacy copper and offering capabilities that wireless simply cannot match at scale. However, adoption still involves cost and design trade-offs that organisations must evaluate carefully.

Key advantages of fibre for business:

• Extremely high bandwidth – Single fibres support 100 Gbps or more, with upgrade paths to 400G and beyond by changing only the transceivers

• Low latency – Light travels faster than electrical signals in copper, and fibre paths are typically more direct than legacy networks

• Long distance reach – Spans of 10-80 km without amplification, and thousands of kilometres with amplified systems

• Immunity to electromagnetic interference – Fibre carries signals as light, unaffected by power lines, radio transmitters, or solar activity that disrupts copper wire

• Enhanced security – Optical fibre is extremely difficult to tap without detection, unlike copper cables or wireless signals

• Future scalability – Existing fibre routes can carry more data by upgrading equipment at either end, protecting infrastructure investment

Key disadvantages and challenges:

• Higher initial installation cost – Cabling, fusion splicing (achieving less than 0.1 dB loss per splice), civil works, and specialised equipment increase upfront expense compared to copper connections

• Specialised skills required – Installation, testing (using OTDR and power meters), and maintenance demand trained technicians

• Legacy site challenges – Upgrading buildings with only copper phone lines requires new cable runs and potentially disruptive civil works

• Remote location difficulties – Extending fibre to rural or remote sites may be prohibitively expensive without subsidy or long-term volume commitments

Typical business scenarios where fibre delivers clear benefits include multi-site organisations migrating from leased lines to 10G or higher backbone links, migrations from MPLS over copper to Ethernet over fibre for combined cost and performance improvements, and adoption of dedicated fibre for mission-critical workloads requiring guaranteed capacity and latency.

Planning and Deployment Considerations

Decision-makers evaluating fibre should consider several factors before committing to deployment or service contracts.

Distance between sites determines whether dark fibre, lit services, or wireless backup links make sense. A 500-metre campus link has very different economics than a 50-kilometre inter-city connection. Required bandwidth today matters, but so does projected growth over three to five years—fibre’s upgrade flexibility means buying ahead of immediate needs can be cost effective in the long term savings it provides.

Resilience requirements often demand dual-path fibre routes taking physically diverse paths between sites. This protects against fibre cuts from construction or accidents, which cause approximately 80% of outages. Regulatory and wayleave constraints affect how quickly and affordably new fibre can be installed, particularly when digging new ducts or accessing existing infrastructure.

Working with experienced fibre installers is essential for design, route surveys, splicing, and testing. Proper loss budgets ensure that links operate within transceiver specifications, and OTDR testing verifies splice quality and identifies potential issues before they cause failures.

Service-level agreements (SLAs) matter for both lit services and dark fibre. Monitoring and maintenance provisions should be clearly defined, including response times for fault repair. Even dark fibre requires ongoing attention: connector cleaning, periodic testing, and coordination with duct owners for any civil works.

Future of Network Fibre Optics

Although optical fibre itself has existed for decades, advances in optics, modulation, and signal processing continue to increase capacity without replacing the glass already in the ground. The fibre networks installed today will carry signals for twenty years or more, with only the equipment at each end requiring upgrades.

Commercial deployment of 400G wavelengths began around 2020, with 800G systems following shortly after. Research demonstrations have achieved 1.6 Tbps per wavelength and beyond. These advances come from higher-order modulation (such as 64-QAM and above), coherent detection, and sophisticated digital signal processing that compensates for fibre impairments.

The rollout of 5G and future mobile generations depends heavily on fibre. Fibre provides fronthaul from radio units to baseband processing, midhaul between distributed processing sites, and backhaul to core networks. Dense small-cell deployments in urban areas require fibre to each cell site, creating substantial demand for new fibre optic network infrastructure.

Software-defined networking (SDN) and network function virtualisation (NFV) are changing how optical transport networks operate. Rather than static configurations, operators can dynamically adjust wavelength routing, allocate bandwidth on demand, and automate provisioning. This flexibility reduces operational costs and accelerates service delivery.

Emerging Use Cases and Technologies

Growth areas for fibre include edge computing nodes linked by fibre to regional data centres, industrial IoT requiring deterministic low latency fibre connections for automation and control, and smart city infrastructure connecting sensors, cameras, and systems across urban environments. Large volumes of data generated at the edge must travel to processing locations quickly and reliably.

New fibre types and enhancements continue to emerge. Bend-insensitive fibres (G.657) tolerate tight routing in buildings and furniture without signal degradation. Hollow-core fibres, currently under development, promise lower latency by allowing light to travel through air rather than glass (approaching 1.01c versus approximately 0.67c in solid glass). Advanced modulation schemes improve spectral efficiency, extracting more data from each wavelength.

Fibre networks will remain the foundation of digital services for at least the next decade, even as wireless and satellite systems evolve. Wireless technologies depend on fibre backhaul, and satellite links terminate at ground stations connected by fibre to the wider internet. The optic network—whether serving a single building or spanning oceans—provides the capacity that every other technology ultimately relies upon.

Whether you’re upgrading a campus network, connecting data centres, or evaluating fibre broadband for a new office, now is the time to assess your infrastructure and explore how fibre-based connectivity can support your organisation’s current and future requirements. The capacity, reliability, and long term savings that fibre networks provide make them the clear choice for high performance digital infrastructure.