Fiber-optic internet works by converting digital information into light signals and transmitting those signals through thin strands of glass fiber. At the other end, optical networking equipment receives the light and converts the information into a form that routers, computers, and other network devices can use.
Unlike traditional copper-based broadband connections, which carry information using electrical signals, fiber-optic connections use light guided through glass. This allows compatible optical equipment to transmit large amounts of information across long distances with relatively low signal loss.
In a typical fiber-to-the-home connection, the internet provider sends optical signals through its fiber network to an optical network terminal (ONT) at your home. The ONT communicates with your router, which then connects your devices to the internet.
The process combines the physics of light transmission with networking technologies that manage how data moves between customers, internet providers, and other networks.
What Is Fiber-Optic Internet?
Fiber-optic internet is a broadband service that uses optical fiber to carry data through all or part of the connection between a customer and an internet service provider.
A fiber-optic cable contains one or more thin glass fibers engineered to guide light.
Electronic equipment encodes information into optical signals, sends those signals through the fiber, and reconstructs the information at the receiving end.
According to Corning’s explanation of optical fiber, the glass core and surrounding cladding help confine light within the fiber, while high-purity materials reduce the loss of optical energy during transmission.
Fiber is used throughout modern telecommunications infrastructure, including residential broadband networks, business connections, data centers, and long-distance communication systems.
However, not every internet service advertised as fiber uses optical fiber all the way into the home.
Some networks use fiber for long-distance transmission and then deliver the final connection through coaxial cable or another technology.
Fiber-to-the-home (FTTH) services extend optical connectivity to the customer’s premises.
How Does Fiber-Optic Cable Carry Data?
The physical mechanism begins with the interaction between light and specially designed glass.
The Core Guides Light Through the Fiber
An optical fiber contains two important glass regions:
- Core: The central region through which the optical signal propagates.
- Cladding: The surrounding glass region with a lower refractive index, helping confine the optical signal within the core.
The refractive-index difference allows the fiber to guide light along its length.
This is commonly introduced through the principle of total internal reflection.
More precisely, especially in single-mode fibers, optical transmission is described in terms of electromagnetic waves propagating in guided modes.
The important practical result is that light can travel through the fiber without immediately escaping through its sides.
An outer protective coating and cable structure help protect the glass from mechanical damage.
Digital Information Modulates the Light
Internet data is represented as digital information.
Before that information can travel through optical fiber, transmitting equipment converts it into a suitable optical signal.
In many digital optical communication systems, a laser or another optical transmitter changes its emitted light intensity according to an encoded data stream.
The receiving system detects those changes and reconstructs the transmitted information.
More sophisticated optical systems may use additional modulation techniques, but the underlying principle remains the same: information is represented through controlled properties of light.
The optical wavelengths used in telecommunications are commonly in the infrared region, outside the range of human vision.
Therefore, a functioning fiber connection does not normally produce a visible beam that you can see traveling through the cable.
Why Doesn’t the Signal Disappear Along the Cable?
All real optical fibers experience some signal loss.
This is called attenuation.
Optical energy can be lost through absorption, scattering, bending, connectors, splices, and other physical effects.
However, telecommunications fibers are manufactured to keep those losses sufficiently low for practical communication distances.
Corning’s optical fiber technical explanation describes how material purity and fiber construction reduce attenuation.
Single-mode optical fiber is commonly used in residential telecommunications networks because it supports long-distance transmission with suitable optical equipment.
Multimode fiber is more common in shorter-reach environments such as certain data center and building connections.
The glass itself does not decide which website the data belongs to. It provides the physical transmission path.
Networking equipment and protocols handle the organization, addressing, and delivery of the information.
How Does Fiber-Optic Internet Work Step by Step?
Consider a home with a fiber-to-the-home (FTTH) connection.
A typical path looks like this:
Laptop → Router → ONT → Fiber Network → ISP → Internet
When information returns from the internet, it travels in the opposite direction.
Many residential FTTH networks use Passive Optical Network (PON) technology. The following example explains that common architecture.
Step 1: Your Device Sends Data to the Router
Suppose you open a website on your laptop.
The browser generates a request, and your operating system prepares the information for network transmission.
The laptop sends the traffic through Wi-Fi or Ethernet.
Your router determines where the packets should be forwarded.
If the destination is outside your local network, the router normally sends the traffic toward its connection with the internet provider.
The router may connect to the ONT through an Ethernet cable.
Some fiber gateways combine routing and optical termination in one device, so the components may not always appear as separate boxes.
Step 2: The ONT Prepares Data for Optical Transmission
The optical network terminal, or ONT, connects your premises to the provider’s optical access network.
It receives traffic from the home network through its supported interfaces.
The ONT then processes the information according to the optical access technology being used.
In a typical PON deployment, this involves placing user traffic into the framing and transmission structure required by the PON system.
The ONT’s optical transmitter converts the information into an optical signal that can travel toward the provider’s equipment.
The ONT is therefore a bridge between the optical access network and the services available inside the home.
It does not create the internet connection independently. It must communicate with compatible equipment operated by the provider.
Step 3: Light Travels Through the Fiber Network
The ONT sends the upstream optical signal through the fiber connected to the home.
In many PON systems, the connection passes through a passive optical splitter before reaching the provider’s optical line terminal (OLT).
The splitter allows multiple customer fibers to share a feeder fiber.
It does not need an electrical power supply to perform its basic splitting or combining function.
In the upstream direction, the optical network combines traffic from customer branches toward the provider.
However, the customers cannot all transmit overlapping upstream signals at arbitrary times.
The optical network uses access-control mechanisms to coordinate transmission.
This is one of the responsibilities of the PON system.
Step 4: The OLT Receives the Optical Data
The optical line terminal, or OLT, is equipment located within the provider’s optical access infrastructure.
It manages communication with multiple ONTs.
The OLT receives upstream optical transmissions, processes the relevant protocol frames, and forwards the customer traffic toward the provider’s network.
According to Cisco’s PON architecture documentation, the OLT is responsible for functions such as traffic scheduling and bandwidth allocation in a GPON network.
The OLT is not the final destination for an ordinary website request.
It provides access between the shared optical distribution network and the ISP’s wider infrastructure.
Step 5: The ISP Forwards the Data Toward Its Destination
After reaching the provider’s network, the traffic can pass through aggregation equipment, routers, and other network connections.
The internet service provider uses routing and interconnection arrangements to reach the destination network.
For example, the requested website might be hosted by a cloud provider connected to the ISP through a direct interconnection or another network.
The packets may cross multiple independent networks before reaching their destination.
These later network segments might also use optical fiber, but they are not necessarily part of the customer’s residential FTTH access network.
This is the broader system explained in How Does the Internet Work?.
Step 6: The Website Response Returns to the Provider
The destination server processes the request and sends a response.
The response travels through the internet toward your ISP.
The ISP then forwards the information through its network to the appropriate optical access system.
The OLT prepares downstream traffic for delivery through the PON.
In a shared PON network, downstream transmissions are distributed through the optical splitter toward the connected customer ONTs.
Each ONT identifies the information it is authorized and configured to receive.
PON technologies include mechanisms for separating and protecting customer traffic on this shared medium.
Step 7: The ONT Converts Incoming Optical Signals
Your ONT receives the downstream optical signal.
Its optical receiver detects the transmitted signal, and the device’s electronics recover the encoded information.
The ONT processes the relevant protocol frames and makes the customer traffic available through its local interfaces.
For example, it can deliver Ethernet traffic toward your home router.
The router then forwards the information to the laptop.
Your browser receives the website response and processes the resources needed to display the page.
The complete process happens repeatedly as your devices exchange information with online services.
What Is a Passive Optical Network (PON)?
A Passive Optical Network is a fiber access architecture that allows a provider to connect multiple customer endpoints using shared optical infrastructure.
The name passive refers to the use of optical distribution components that do not require local electrical power for their basic operation.
The two endpoint devices, the OLT and ONT, are still powered electronic equipment.
A typical PON includes:
| Component | Main Function |
|---|---|
| OLT | Manages the optical access network on the provider side |
| Feeder fiber | Carries optical signals between the OLT and distribution network |
| Passive optical splitter | Divides or combines optical signals across multiple fiber branches |
| Distribution/drop fiber | Connects the splitter network to customer premises |
| ONT | Terminates the optical connection at the customer location |
A common point-to-multipoint arrangement is:
One OLT Port → Shared Fiber → Optical Splitter → Multiple ONTs
Cisco’s overview of passive optical networking explains how this arrangement reduces the need for separate feeder fibers and powered distribution equipment.
What Does an Optical Splitter Actually Do?
An optical splitter divides incoming optical power among multiple output fibers.
For example, a 1:32 splitter can connect one optical input to 32 output paths.
The splitter does not create 32 independent full-capacity connections.
Instead, compatible PON equipment manages how the shared optical transmission capacity is used by the connected customers.
Splitting optical power also introduces loss.
The more branches a network uses, the more carefully the provider must manage its optical power budget, signal quality, and deployment distance.
The supported split ratio depends on the PON standard, equipment, and network design.
How Do Multiple Homes Share One Fiber?
A PON uses different techniques for downstream and upstream traffic.
Downstream traffic: The OLT transmits information that reaches multiple ONTs through the passive optical distribution network. Each ONT processes the frames intended for it, with customer traffic protection provided by the relevant PON security mechanisms.
Upstream traffic: Different ONTs transmit at scheduled times so their signals do not collide at the OLT.
This upstream method is a form of Time-Division Multiple Access (TDMA).
The OLT assigns suitable transmission opportunities, and the ONTs follow the timing instructions.
The ITU-T GPON transmission convergence specification, G.984.3, defines upstream multiple access, bandwidth assignment, activation, and other mechanisms.
These controls help a provider use a shared optical connection efficiently.
However, shared capacity remains finite.
When many customers use substantial bandwidth simultaneously, demand can affect the performance available to individual users.
How Does Fiber Carry Uploads and Downloads at the Same Time?
A fiber connection needs to carry information in both directions.
Downloads travel from the provider toward your home.
Uploads travel from your home toward the provider.
Many PON systems use different optical wavelengths for the two directions.
This technique is called Wavelength-Division Multiplexing (WDM).
The different wavelength bands allow upstream and downstream signals to share a single fiber without being treated as the same optical channel.
For example, conventional GPON commonly uses:
| Direction | Typical GPON Wavelength |
|---|---|
| Downstream | Approximately 1490 nanometers |
| Upstream | Approximately 1310 nanometers |
XGS-PON uses different wavelength bands, including approximately 1577 nanometers downstream and 1270 nanometers upstream in common deployments.
Cisco’s PON technology explanation describes these wavelength arrangements.
Using separate wavelengths does not mean every customer has exclusive use of the shared fiber capacity.
The system still needs scheduling, framing, and bandwidth management.
What Is the Difference Between GPON and XGS-PON?
GPON and XGS-PON are different generations of passive optical access technology.
Both use fiber-optic infrastructure and point-to-multipoint optical distribution networks.
However, their transmission capacities and technical requirements differ.
| Technology | Typical Nominal Downstream Line Rate | Typical Nominal Upstream Line Rate |
|---|---|---|
| GPON | Approximately 2.5 Gbps | Approximately 1.25 Gbps |
| XG-PON | Approximately 10 Gbps | Approximately 2.5 Gbps |
| XGS-PON | Approximately 10 Gbps | Approximately 10 Gbps |
These are nominal optical access line rates, not guaranteed speeds for each subscriber.
The ITU-T GPON specifications describe gigabit-capable passive optical access.
The ITU-T XGS-PON specification, G.9807.1, defines a system with nominal 10 Gbps capacity in both directions.
Why Are XGS-PON Speeds Symmetrical?
The letter S in XGS-PON refers to symmetric capability.
The system supports approximately equal nominal transmission capacity in the downstream and upstream directions.
This makes it suitable for services requiring substantial upload capacity as well as download capacity.
For example, uploading large video files, sending backups to cloud storage, and transmitting live video can benefit from higher upstream capacity.
However, an XGS-PON connection does not automatically mean that every customer receives a 10 Gbps symmetrical subscription.
Providers can offer different service plans using the same underlying technology.
Can GPON and XGS-PON Use the Same Fiber?
In some deployment designs, yes.
Compatible systems can coexist over a shared optical distribution network using appropriate wavelength arrangements and coexistence equipment.
This can allow providers to upgrade service capabilities while reusing portions of their installed fiber infrastructure.
However, upgrading may require changes to the provider’s equipment and the ONT at the customer’s premises.
A GPON ONT cannot simply operate as an XGS-PON ONT through an ordinary software setting if its optical hardware does not support the required standard.
Does All Fiber Internet Use a Passive Optical Network?
No.
PON is common in residential FTTH deployments, but it is not the only architecture.
Some optical access networks use dedicated point-to-point connections.
In a point-to-point design, a subscriber can have a dedicated optical path to an appropriate provider endpoint instead of sharing one PON port through a passive splitter.
Active Ethernet deployments may use powered switching equipment within the distribution infrastructure.
| Architecture | Main Characteristic |
|---|---|
| PON | Multiple subscribers share an optical distribution structure through passive splitters |
| Point-to-point fiber | A dedicated optical path connects the subscriber to a provider-side endpoint |
| Active optical network | Powered switching or distribution equipment may be used between endpoints |
ITU-T’s optical access network topology guidance describes both point-to-point and point-to-multipoint architectures.
A dedicated optical connection does not guarantee unlimited internet bandwidth.
The provider’s aggregation network, upstream connectivity, service configuration, and destination systems can still impose performance limits.
Does Fiber Internet Need a Modem?
Fiber-to-the-home internet typically uses an ONT rather than a conventional cable or DSL modem.
A cable modem uses DOCSIS signaling over coaxial infrastructure.
A DSL modem communicates through compatible copper telephone wiring.
An ONT communicates through a supported optical access network.
The devices serve related access-network roles, but their physical interfaces and signaling standards differ.
Some internet providers refer to an ONT or combined gateway as a fiber modem.
The term is understandable informally, but optical network terminal is more precise when discussing a PON connection.
The differences between access equipment are explained in How Does a Modem Work?.
ONT vs. Router: What’s the Difference?
The ONT terminates the optical access connection.
The router forwards IP traffic between the local network and other networks.
A typical home installation is:
Fiber Cable → ONT → Router → Wi-Fi and Ethernet Devices
Some products combine ONT and router functionality in one gateway.
Others use a separate ONT connected to a standalone router.
The network functions remain conceptually different even when they are housed in one device.
Does Fiber Internet Require Wi-Fi?
No.
Wi-Fi provides wireless connectivity inside the home.
Fiber provides the optical connection to the internet provider.
A desktop computer can use fiber internet through a wired Ethernet connection without communicating over Wi-Fi.
Likewise, a smartphone can connect to a Wi-Fi router that uses fiber as its upstream internet connection.
The two technologies work together but operate over different physical media.
What Is the Difference Between FTTH, FTTB, and FTTN?
The term fiber internet can describe different network designs.
The most important distinction is where the optical fiber ends.
| Network Design | Meaning | Where Fiber Typically Reaches |
|---|---|---|
| FTTH | Fiber to the Home | The individual home |
| FTTP | Fiber to the Premises | A home or other customer premises |
| FTTB | Fiber to the Building | A building, with potentially different internal distribution |
| FTTN | Fiber to the Node | A neighborhood or distribution node |
For FTTH, fiber extends to the customer premises.
For FTTB, the building may receive fiber while individual apartments use Ethernet or another internal connection method.
For FTTN, the last portion of the customer connection may use copper wiring or another technology.
This matters because performance depends on the technology used across the actual access path.
A broadband service that uses fiber somewhere in the provider’s network is not necessarily equivalent to a direct FTTH connection.
How Does Fiber Internet Compare with Cable Internet?
Fiber internet and cable internet both provide broadband connectivity, but their access technologies differ.
Fiber-to-the-home services carry customer access traffic over optical fiber.
Cable internet commonly uses hybrid fiber-coaxial infrastructure, where fiber serves parts of the provider network and coaxial cable connects portions of the local access system.
DOCSIS provides the technical standards used for cable broadband communication.
| Feature | Fiber-to-the-Home Internet | Cable Internet |
|---|---|---|
| Typical final access medium | Optical fiber | Coaxial cable |
| Signal type | Optical | Radio-frequency electrical signals |
| Common access architecture | PON or point-to-point fiber | Hybrid fiber-coaxial network |
| Customer access equipment | ONT or compatible optical gateway | Cable modem or integrated gateway |
| Upload capacity | Depends on optical technology and service plan | Depends on DOCSIS technology and network configuration |
| Susceptibility to electromagnetic interference in the access medium | Fiber itself is highly resistant | Coaxial systems use shielding and are subject to relevant RF impairments |
Fiber access can offer substantial upload capacity and flexibility for future technology upgrades.
However, it would be inaccurate to say that every fiber subscription is faster than every cable subscription.
Both technologies support different generations, equipment capabilities, and service plans.
Actual performance must be evaluated at the service level.
Why Is Fiber-Optic Internet Often Fast?
Fiber supports high-capacity communication because optical systems can encode information at substantial data rates and transmit it across long distances with comparatively low attenuation.
Several characteristics contribute to its capabilities.
High-Capacity Optical Transmission
Compatible optical transmitters and receivers can exchange information at high data rates.
Multiple wavelength channels can also be used in certain optical networking systems to expand transmission capacity.
The achievable capacity depends on the optics, standards, network design, and equipment rather than the glass fiber alone.
Low Signal Loss
Properly designed optical fiber can transmit signals over long distances with relatively low attenuation.
This makes it suitable for access networks, metro networks, and long-haul infrastructure.
However, every deployment has an optical power budget.
Connector losses, bends, fiber length, and splitting losses must remain within the supported limits.
Upgradable Equipment
Providers can sometimes deploy newer optical equipment while reusing existing fiber cable infrastructure.
For example, a suitable network may be upgraded from GPON to XGS-PON by changing compatible active equipment and optical service configurations.
This does not mean every installation can be upgraded without construction or infrastructure work.
The installed fiber, splitter design, optical loss budget, and network architecture must support the new equipment.
Does Fiber Internet Have Lower Latency?
Fiber internet can provide low-latency connectivity, but fiber does not automatically guarantee the lowest possible latency.
Latency is the time required for information to travel through a network path.
It includes several types of delay:
- Signal propagation through physical media.
- Processing by networking equipment.
- Time spent waiting in transmission queues.
- Protocol and application-related delays.
Optical fiber carries information through light, but that light travels more slowly through glass than through a vacuum.
The propagation characteristics alone do not explain every performance difference between fiber and other broadband technologies.
Fiber access networks can offer favorable latency because of their transmission design, available capacity, and network architecture.
However, congestion, routing, wireless connectivity, and distant servers can still introduce significant delays.
For example, a fast FTTH connection cannot eliminate the network distance between a user in New York and a server located in another continent.
The route selected by internet routing also influences the total delay.
Fiber is an excellent transmission medium, but it cannot remove every source of latency beyond the optical link.
Is Fiber Internet Faster for Uploads?
Fiber internet can provide high upload speeds, particularly when the provider uses a suitable optical access technology and offers a symmetrical service plan.
However, fiber does not inherently guarantee symmetrical speeds.
For example, a GPON system commonly has a higher nominal downstream line rate than upstream line rate.
XGS-PON supports approximately equal nominal capacities in both directions.
The actual subscription may still impose different download and upload limits.
A provider might offer a service with equal advertised speeds, or it might configure the service asymmetrically for commercial or network-planning reasons.
The useful distinction is between:
- Technology capacity: What the underlying network equipment can support.
- Service-plan speed: What the provider makes available to a particular subscription.
- Actual throughput: What the customer’s devices achieve under real operating conditions.
These numbers are related but not necessarily identical.
Can Fiber Internet Still Become Slow?
Yes.
A fiber connection can have substantial available capacity while a particular application performs poorly.
Several potential bottlenecks exist.
Wi-Fi Limitations
The optical connection may be functioning correctly while wireless performance is limited by signal strength, interference, distance, or the capabilities of the connected devices.
For example, a laptop in a distant room may experience lower throughput than a computer connected directly through Ethernet.
Router and Ethernet Port Capacity
The router and network interfaces must support the desired service speed.
A multi-gigabit fiber subscription cannot deliver its full capacity through a network port that supports a lower maximum link rate.
The router must also have adequate processing and forwarding capacity.
Ethernet provides common wired local-network connections, but different Ethernet interface standards support different data rates.
Shared Access Capacity
In PON networks, multiple subscribers share portions of the access system.
The OLT manages transmission opportunities and available bandwidth.
If simultaneous demand approaches the shared capacity, customer traffic may experience congestion.
ISP and Internet Congestion
Traffic must also pass through the ISP’s aggregation and core infrastructure and potentially other independently operated networks.
A bottleneck can exist outside the optical access network.
Remote Server Performance
A website or download server may be unable to deliver information at the full rate supported by the customer’s fiber subscription.
Consequently, a slow download does not necessarily mean the optical connection is malfunctioning.
What Happens If a Fiber-Optic Cable Is Damaged?
Optical fiber requires a continuous, sufficiently low-loss transmission path.
A damaged fiber can cause attenuation, intermittent errors, or a complete loss of optical communication.
Common causes include physical cuts, damaged connectors, excessive bending, contamination, and improper splicing.
A severe cable break can prevent the ONT from receiving the expected downstream optical signal.
In a typical PON installation, the ONT may display an optical signal or connection alarm.
The indicator names and colors depend on the device manufacturer and model.
A fiber-optic connection is resistant to electromagnetic interference in the glass transmission medium, but that does not make it immune to physical damage.
Can You Repair Fiber Cable Like an Ethernet Cable?
Not in the same way.
Fiber repair often requires appropriate optical connectors, splicing equipment, testing instruments, and installation procedures.
Poor repairs can introduce additional loss or reflections that degrade performance.
Customers should not look directly into optical connectors or attempt to inspect an active fiber by eye. Telecommunications optical sources may emit invisible infrared light.
A damaged provider fiber should generally be inspected and repaired by qualified personnel.
Does Fiber Internet Work During a Power Outage?
Not necessarily.
The passive optical splitter does not require local electrical power.
However, the ONT, router, and provider-side OLT are active electronic devices.
They require electricity.
If your home loses power, the ONT and router may shut down unless they have a compatible backup power source.
Even with backup power at home, the service also depends on the provider’s relevant powered network equipment remaining operational.
A battery backup or uninterruptible power supply may keep compatible home networking equipment running for a limited period.
However, the duration depends on the equipment’s power consumption, battery capacity, and configuration.
The passive nature of PON distribution does not mean that the complete fiber internet service operates without electricity.
What Should You Check If Fiber Internet Stops Working?
A fiber connection problem can occur at different points between the provider’s network and your device.
Start by identifying whether the failure affects the optical link, the router, or only one device.
| Symptom | Possible Explanation |
|---|---|
| ONT indicates loss of optical signal | Fiber path, connector, optical equipment, or provider-side issue |
| ONT appears connected but router has no internet | WAN configuration, Ethernet connection, authentication, or provider network issue |
| Wired connection works but Wi-Fi does not | Wireless configuration, interference, or access point problem |
| Only one website fails | DNS, routing, server, or application issue |
| Connection is slow on every device | Access link, network congestion, router capacity, or another shared bottleneck |
The first practical checks are whether the ONT and router have power, whether the Ethernet connection between them is secure, and whether the provider has reported an outage.
Consult the equipment manufacturer’s documentation before interpreting particular status lights.
Avoid factory-resetting a provider-managed ONT unless instructed to do so.
If the ONT reports an optical signal problem, repeated router restarts are unlikely to repair a physically damaged fiber connection.
Does Fiber-Optic Internet Use Light Across the Entire Internet?
Not necessarily.
The fiber-optic access connection is only one segment of the complete path.
After traffic enters the provider’s network, it may pass through different types of infrastructure.
Much of the internet’s high-capacity backbone uses optical fiber, including terrestrial and submarine communication cables.
However, traffic may also cross wireless links, Ethernet networks, data center infrastructure, and other communication systems.
A fiber-to-the-home subscription means the provider delivers optical access to the premises.
It does not imply that every device, router, server, or network segment involved in the communication uses optical fiber.
The internet works because multiple communication technologies carry compatible network traffic between interconnected systems.
Fiber Internet Turns Light Into Network Connectivity
Fiber-optic internet works by encoding data into optical signals that travel through specially designed glass fibers.
At the customer’s premises, an ONT communicates with the provider’s optical access system and makes the connection available to home networking equipment.
In a typical PON deployment, an OLT manages several customer ONTs through a shared optical distribution network. Passive splitters distribute optical signals, while protocol mechanisms coordinate downstream delivery and upstream transmission.
Technologies such as GPON and XGS-PON define how this shared optical connection operates and how much nominal transmission capacity it supports.
The actual internet experience also depends on the router, Wi-Fi, service plan, provider infrastructure, and destination systems.
The fundamental advantage of fiber is not simply that it uses light. It is that carefully engineered optical communication systems can carry large amounts of information over long distances through a highly capable physical transmission medium.