How Fibre Optics Transmits Data at Lightning Speeds

Quick Answer: Why Fibre Optics Is So Fast

Fibre optic cables send data as laser or LED light pulses through thin strands of ultra-pure glass, travelling at approximately 200,000 kilometres per second—roughly two-thirds the speed of light in a vacuum. This light-based approach delivers unparalleled speed and capacity compared to traditional copper cables.

This superior performance enables multi-gigabit and even terabit-per-second links across cities, countries, and undersea routes. The same underlying fiber optic technology powers everything from home fibre broadband connections to massive data centres, 5G mobile backhaul, and the global internet backbone that keeps the world connected.

Key benefits of fibre optics at a glance:

• Speed: Supports gigabit and terabit data rates for fast data transmission

• Distance: Carries signals over very long distance links with minimal signal loss

• Reliability: Provides stable connection quality unaffected by environmental factors

• Capacity: Enables multiple wavelengths to carry data simultaneously on a single fibre

Fibre Optics in Plain Terms

Think of fibre optics as sending data using light rather than electricity. A single fibre strand is essentially a transparent glass or plastic hair that carries rapid flashes of light from one point to another. Each flash—or light pulse—represents digital bits (the 0s and 1s that make up all digital information) encoded by high-speed lasers or LEDs.

These transmitters operate at specific infrared wavelengths, commonly 850 nm, 1310 nm, and 1550 nm. Because light can switch on and off extremely fast—billions of times per second—fibre cables can carry enormous amounts of data simultaneously across long distances without breaking a sweat.

The fundamental difference: Traditional copper cables carry data as changes in electrical voltage or electrical current. Fiber optic strands carry data as light pulses—rapid flashes that travel far faster and with greater bandwidth than electrical signals ever could.

This difference is why optical fibre has become the backbone of modern telecommunications. When you’re streaming 4K video, gaming online, or making a video call, there’s a good chance those light signals travel through fibre at some point along the journey.

Inside a Fibre Optic Cable: Structure and Materials

A typical telecom fibre is a strand of ultra-pure glass about 125 µm in diameter—roughly the width of a human hair. These glass or plastic fibers are grouped in bundles inside protective cables designed to survive harsh conditions from underground ducts to ocean floors.

The three main parts of a single optical fibre:

Component	Description	Typical Size
Core	The central region where light travels	8–9 µm (single-mode) or 50–62.5 µm (multimode)
Cladding	Surrounds the core with a lower refractive index to keep light trapped	125 µm total diameter
Coating/Buffer	Protective layers providing mechanical strength	Varies by application

The cladding is crucial—its slightly lower refractive index compared to the core creates the conditions for total internal reflection, which keeps light bouncing along the inner walls of the fibre rather than escaping through the sides.

Outdoor fibre cables often include additional protection:

• Aramid yarn (similar to Kevlar) for tensile strength

• Gel or dry water-blocking materials to prevent moisture damage

• Metal armour for rodent protection in buried applications

• Heavy-duty outer jackets for undersea cables

Large backbone cables can contain hundreds of individual optical fibers, each capable of carrying multiple high-capacity channels using wavelength-division multiplexing (WDM). This means a single cable no thicker than a garden hose can transmit more data than entire cities produced just decades ago.

How Light Stays Inside the Fibre

The physics that makes fibre optics work is called total internal reflection. This principle keeps light bouncing inside the fibre core instead of escaping through the edges, allowing optical signals to travel tens or hundreds of kilometres without leaking away.

Here’s how it works: the core has a slightly higher refractive index than the surrounding cladding. When light travelling through the core hits the boundary with the cladding at a shallow angle, it reflects back into the core rather than passing through. This happens continuously along the entire length of the fibre, guiding light pulses from source to destination.

Simple analogy: Imagine a perfectly polished mirror-lined tunnel. Light entering one end bounces off the inner walls at shallow angles, sliding along the length of the tunnel until it emerges at the far end. That’s essentially what happens inside a fibre—except the “mirrors” are created by the difference in refractive index between core and cladding.

Fibre designers carefully choose the core size and refractive index profile to minimise dispersion—the tendency for pulses to spread out over distance. Step-index fibres have an abrupt change in refractive index between core and cladding, while graded-index multimode fibers have a gradual transition that helps keep pulses tighter over longer runs.

From Electricity to Light and Back Again

Your computer, smartphone, and router all work with electrical signals. Fiber optic connectivity requires converting these electrical signals into light at one end, transmitting them through the fibre, and then converting them back to electrical form at the other end.

At the transmitter:

Laser diodes (typically operating at 1310 nm or 1550 nm for long-haul single mode fiber) or LEDs (often 850 nm for short multimode fiber links) convert electrical data into modulated light. These devices switch the light’s intensity, phase, or frequency to represent the binary data—essentially creating a stream of light pulses that encode information.

At the receiver:

Photodiodes (photodetectors) sense the incoming light waves and convert them back into electrical signals. Networking equipment then processes these signals, extracting the original data and routing it to its destination.

Common line speeds in modern networks include:

• 1 Gbit/s for many business and residential connections

• 10 Gbit/s for enterprise and data centre interconnects

• 100 Gbit/s for carrier backbone links

• 400 Gbit/s and beyond for cutting-edge systems

These speeds are carried over standardised interfaces like 10GBASE-LR or 100GBASE-LR4, ensuring equipment from different manufacturers can work together seamlessly.

Light Pulses vs. Electrical Signals

Understanding why fibre optics outperforms copper requires comparing how each medium handles data transmission. Unlike traditional copper cables, which carry data as voltage changes through copper wire, fibre transmits information as light confined within glass.

Key limitations of copper:

Factor	Impact on Copper	Fibre Advantage
Resistance	Signal weakens over distance	Minimal attenuation in glass
Capacitance	Limits high-frequency signals	Light frequencies unaffected
Electromagnetic interference	Picks up electrical noise from nearby sources	Complete immunity to electromagnetic interference
Distance	~100 metres at high speeds	Tens to hundreds of kilometres

Copper cables—whether twisted pair Ethernet or coaxial cable—act somewhat like antennas, picking up interference from power lines, motors, radio transmitters, and even lightning strikes. This electrical noise degrades signal integrity and limits reliable transmission distances.

Light in optical fibers, by contrast, is immune to electromagnetic fields, radio signals, and external interference. Signals stay much cleaner and can travel far greater distances with fewer repeaters or amplifiers.

Practical comparison: Most copper Ethernet runs are limited to about 100 metres before signal degradation becomes problematic. Comparable fibre links can span tens of kilometres at similar data rates—sometimes without any active equipment in between.

Why Fibre Optics Achieves Such High Bandwidth

Bandwidth depends on how fast a medium can switch between states and how many distinct channels can be used in parallel. Both factors favour light over electricity by enormous margins.

Optical carriers operate at incredibly high frequencies—hundreds of terahertz compared to the megahertz or low gigahertz ranges used in copper systems. This allows fiber optic technology to support extremely high bit rates and advanced modulation formats like QPSK and 16-QAM on each wavelength, packing more data into every pulse.

Wavelength-Division Multiplexing (WDM)

The real breakthrough for high speed data transmission comes from wavelength-division multiplexing. WDM sends dozens or even hundreds of separate colours (wavelengths) of light down the same fibre simultaneously, each carrying its own independent data stream.

Dense WDM (DWDM) pushes this further, packing wavelength channels as close as 0.4 nm apart. A single fibre pair in modern systems can carry:

• 80-100+ individual wavelength channels

• Each channel operating at 100 Gbit/s to 400 Gbit/s

• Total capacity exceeding 10 Tbit/s per fibre pair

Modern undersea cables launched in the 2020s deliver multiple terabits per second per fibre pair using dense WDM and coherent optics. These submarine cables—spanning thousands of kilometres across ocean floors—carry over 99% of international data traffic, connecting continents with lightning speed capacity.

Single-Mode vs Multimode Fibre

The two main types of optical fibre—single mode fibre and multimode fiber—serve different purposes based on their core size, distance capability, and cost.

Single-Mode Fibre

Single mode fibre features a tiny core of approximately 8–9 µm, supporting just one light path (mode). This design eliminates modal dispersion, allowing signals to travel enormous distances without significant pulse spreading.

Characteristics:

• Core size: ~8–9 µm

• Wavelengths: 1310 nm and 1550 nm

• Distance: Tens to hundreds of kilometres

• Applications: Metro networks, long-haul links, undersea cables

• Transmitters: Laser diodes for precise, narrow beams

Multimode Fibre

Multimode fiber has a larger core (50 µm or 62.5 µm) that supports multiple modes of light travelling along different paths. While this limits distance, it reduces alignment precision requirements and uses less expensive light sources.

Characteristics:

• Core size: 50 µm (OM3/OM4/OM5) or 62.5 µm (legacy OM1/OM2)

• Wavelength: Typically 850 nm

• Distance: Tens to hundreds of metres

• Applications: Data centres, campus networks, building risers

• Transmitters: VCSELs (Vertical-Cavity Surface-Emitting Lasers)

Data centre specifications: OM3 multimode fibre supports 10 Gbit/s links up to 300 metres, while OM4 extends this to 400 metres. OM5 adds support for short-wave WDM, enabling 100 Gbit/s over 150 metres using multiple wavelengths—ideal for dense data centre interconnects.

Reducing Signal Loss and Preserving Speed Over Distance

Although fibre has remarkably low attenuation compared to copper, signal loss and pulse spreading still occur over long distances. Managing these effects is essential for maintaining reliable connections across continents and oceans.

Attenuation in Modern Fibre

Modern single mode fiber achieves attenuation as low as 0.2 dB/km at 1550 nm wavelength—a testament to the incredible purity of today’s optical glass. This low signal loss allows links of 80–100 km between amplifiers in many backbone systems, compared to copper’s requirement for repeaters every few hundred metres.

Keeping Signals Strong

Several technologies maintain signal power and reduced signal degradation over extreme distances:

• Erbium-Doped Fibre Amplifiers (EDFAs): Boost optical signals directly without converting to electrical form, typically placed every 60–100 km on long-haul routes

• Dispersion Compensation: Special fibres or modules counteract pulse spreading caused by different wavelengths travelling at slightly different speeds

• Coherent Detection: Advanced receivers that can extract more information from degraded signals, pushing capacity limits

Real-world example: Transatlantic fibre cables commissioned after 2016 use optical amplification and coherent detection to achieve multi-terabit capacities across distances exceeding 6,000 km. These systems maintain signal integrity through dozens of amplifier stages, delivering reliable connections between continents.

Fibre Optics in Modern Broadband Networks

National broadband rollouts increasingly rely on optical fibre to meet growing data demands from 4K streaming, cloud services, remote work, and online gaming. Full fibre installation has become the gold standard for residential and business connectivity.

Common Fibre Architectures

Architecture	Description	Typical Speed
FTTC/FTTN	Fibre to the cabinet/node, copper for the last 200–500 metres	30–80 Mbit/s
FTTP/FTTH	Fibre to the premises/home, fibre runs directly to the building	100 Mbit/s to 1+ Gbit/s
PON	Passive Optical Network sharing fibre among multiple premises	Varies by technology

Fibre to the premises (FTTP) delivers maximum performance by eliminating the copper bottleneck entirely. PON technologies like GPON, XGS-PON, and 10G-PON share a single fibre among multiple homes using optical splitters—no active electronics in the field means lower maintenance and higher reliability.

What Full Fibre Can Deliver

Consumer speed tiers available on full fibre connections in many cities include:

• 300 Mbit/s symmetrical—ample for most households

• 500 Mbit/s symmetrical—heavy streaming and work-from-home families

• 1 Gbit/s (1000 Mbit/s) symmetrical—power users and small businesses

• 2+ Gbit/s—emerging options for the most demanding applications

These symmetric speeds mean uploads match downloads—critical for video conferencing, cloud backups, and content creation that older asymmetric services handled poorly.

Everyday Benefits for Home and Office Users

Fibre’s technical strengths translate directly into better everyday experiences. High bandwidth and low latency mean smooth 4K and 8K video streaming, responsive online gaming, and crystal-clear video conferencing without the buffering, lag, or frozen screens that plague slower connections.

Multiple Devices, No Compromise

Modern households often have dozens of connected devices—smartphones, tablets, laptops, smart TVs, gaming consoles, and IoT devices. Fibre’s greater bandwidth means multiple devices can operate simultaneously without competing for limited capacity:

• Three family members streaming different Netflix shows

• A teenager gaming online with low ping

• A parent on a video conference call

• Smart home devices maintaining their connections

• Cloud backups running in the background

All of this can happen on a well-provisioned fibre connection without noticeable impact on any individual activity. This enables efficient communication and reliable connections that keep pace with how we actually live and work.

Symmetric Speeds Matter

Many full-fibre plans offer symmetric upload and download speeds. This supports activities that traditional asymmetric connections struggle with:

• Backing up photos and videos to cloud storage

• Hosting video calls where your camera quality matters as much as what you’re watching

• Uploading large media files for work or content creation

• Running home servers or self-hosted applications

Practical scenario: A remote worker can run several simultaneous video calls while others in the household stream ultra-HD content, with everyone enjoying uninterrupted connectivity. Try that on an old ADSL line.

Critical Uses: Data Centres, Finance, and Emergency Services

Beyond home broadband, fibre optics underpins mission-critical networks where speed, reliability, and low latency directly affect outcomes—from financial transactions to emergency response.

Data Centres and Cloud Infrastructure

Modern data centres rely on high-density fibre for interconnects between servers, storage systems, and network equipment. These facilities use 40G, 100G, and increasingly 400G optical links to synchronise services across facilities within milliseconds.

Cloud providers deploy fibre cables extensively within and between their data centres, ensuring that your cloud applications respond quickly regardless of where the underlying servers are physically located. This fiber optic infrastructure handles the petabytes of data transfer that power streaming services, social media, and enterprise applications.

Financial Trading Networks

In financial markets, microseconds matter. Ultra-low-latency fibre routes between exchanges in cities like London, New York, and Tokyo are engineered to minimise round-trip times. Trading firms invest heavily in the shortest, fastest fibre paths because faster execution can mean significant improvements in trading outcomes.

These networks use the most advanced coherent optics and careful route engineering to shave every possible microsecond from transmission times—a world where light’s finite speed through glass becomes a competitive consideration.

Emergency Services

Ambulance, fire, and police services rely on fibre backbones to carry:

• Live video feeds from body cameras and vehicles

• Digital radio communications

• Real-time mapping and location data

• Patient information transmitted to hospitals en route

• Dispatch systems coordinating response

These networks require high availability even during severe weather or power disturbances. Fibre’s immunity to electromagnetic interference makes it more resilient than copper alternatives in challenging environments.

Immune to Electromagnetic Interference and Eavesdropping

One of fibre’s numerous advantages is complete immunity to electromagnetic interference. Because the signal is light confined within glass, fibre cables don’t act as antennas and remain unaffected by nearby electrical noise.

Where This Matters Most

Environments with heavy electrical interference that would cause problems for copper include:

• Industrial facilities with large motors and welding equipment

• Rail corridors with high-voltage traction power

• Hospitals with MRI machines and other medical equipment

• Data centres with dense electrical equipment

• Areas prone to lightning strikes

In these settings, fibre optics provides stable, interference-free data security and signal integrity that copper simply cannot match. The light signals travel through the glass core completely isolated from the electromagnetic chaos outside.

Physical Security Advantages

Tapping a fibre link is technically challenging and usually detectable. Unlike copper cables where signals can sometimes be intercepted from a distance using inductive methods, accessing light in a fibre requires physical intervention that typically causes measurable signal loss or disruption.

Many critical sectors—defence, healthcare, financial institutions—favour fibre for this combination of reliability and inherent physical security. While no system is perfectly secure, fibre raises the bar significantly compared to alternatives.

Recent Advances and the Future of Fibre Speed

Ongoing research continues to push fibre performance, lowering latency and increasing capacity without requiring entirely new cable routes. The technology powering today’s networks represents decades of incremental improvements, and that progress shows no signs of slowing.

Hollow-Core Fibres

Traditional fibre guides light through solid glass, where it travels at about two-thirds the speed of light in vacuum. Hollow-core fibres guide light through air instead, reducing latency by around 30% compared to standard fibre.

Early field trials in the 2020s have demonstrated this technology’s potential for latency-sensitive applications like high-frequency trading and real-time control systems. While not yet widely deployed, hollow-core fibre represents a significant improvement for applications where every microsecond counts.

Expanding Capacity

Several technologies are pushing capacity limits:

• Coherent optics enabling 1 Tbps per wavelength on commercial systems

• Photonic-crystal fibres supporting wider wavelength ranges

• Space-division multiplexing using multiple cores in a single fibre

• New glass compositions handling higher power levels without degradation

Data rates on commercial fibre systems have roughly doubled every few years, a trend expected to continue. These advances support emerging technologies like high-resolution VR streaming, autonomous vehicle coordination, and beyond-5G mobile networks—all of which will demand more data than ever.

What’s Coming

Industry predictions suggest petabit-per-second superchannels by 2030, driven by AI workloads and 6G network requirements. While satellite services like Starlink serve important roles for remote coverage, they cannot match the bandwidth density that fibre optic infrastructure delivers for core network capacity.

Why Fibre Optics Will Remain the Backbone of High-Speed Data

Transmitting data as light through glass combines unmatched speed, distance, bandwidth, and reliability in a single medium. No other technology comes close to matching this combination of characteristics for carrying massive amounts of information over long distance communication links.

Fibre’s core strengths make it the default choice for network upgrades and new infrastructure projects worldwide:

• Low attenuation: Signals travel kilometres without significant degradation

• Massive capacity: Terabits per second on a single strand thinner than a human hair

• Interference immunity: Reliable connections in the noisiest environments

• Physical security: Difficult to tap without detection

When you connect to fibre broadband at home or in your office, you’re tapping into the same fundamental technology that powers undersea cables spanning oceans and the internet backbones connecting continents. Your local fibre optic cable is part of a global network carrying humanity’s data at lightning speed.

While wireless standards and applications will continue to evolve, they will depend on fibre optics behind the scenes to handle ever-growing global data traffic. The plastic fibers or glass strands carrying light pulses today will remain essential infrastructure for decades to come—quietly enabling the high speed internet that modern life increasingly demands.

Whether you’re evaluating a full fibre installation for your home, planning enterprise network upgrades, or simply curious about the technology delivering your streaming content, understanding how fibre optics transmit data helps you appreciate why this technology has become so foundational. From long-haul carrier networks to fibre cables running to your premises, optical fibre remains humanity’s fastest and most reliable way to move information across any distance.