[Blog] A Brief Introduction to Fiber Optic Communications
By Nathanael Winslow, Applications Engineer
In my last blog entry, I explored the critical role of fiber, diving into the fiber technologies that keep the lights (and data) on. In this blog, let's look at the fundamentals of fiber optic communications—how light carries data, the components that make it possible and why fiber is the backbone of modern networks.
Introduction
Before widespread deployment of the telegraph in the mid-1800s, messages could take weeks to travel long distances. Today, information crosses oceans in milliseconds and can reach millions instantly. While many imagine satellites as the work horse of modern long-distance communications, the reality is that most data travels through millions of miles of physical cables buried underground, strung between poles, or laid across the ocean floor. These cables form the backbone of our global telecommunications system, enabling the seamless, high-speed exchange of information that defines modern life. And it all hinges on a revolutionary technology that emerged in the 1960s: fiber optics.
Fiber Optics
Put simply, fiber optics refers to a technology in which data is transmitted as pulses of light which travel along tiny strands of glass, called fibers. The individual fibers are barely thicker than a human hair, but they are surprisingly strong and flexible, considering they are made of glass. Many fibers are bundled together and “packaged” in fiber optic cables, which are designed to protect the fibers from whatever dangers may exist where they are installed.
Compared to other forms of data transmission, like copper cables, satellites, or microwave technologies, fiber optics is superior in almost every way, especially for long-haul applications. The optical signals can travel faster – literally at the speed of light (low latency), travel farther, carry more information (high bandwidth), are immune to electromagnetic interference, can’t be easily tapped into (highly secure), and ultimately have a lower cost of ownership. Learn more about the benefits of fiber optic cable here.
Transmitters and Receivers
The pulses of light are injected into the glass fiber by an LED or laser in a device called an optical transmitter and received at the other end by an optical receiver. The transmitter codes the light and injects it into the fiber. The receiver receives the light, interprets it and converts it into an electrical signal that can be processed by a computer. Sometimes these two devices are combined into one, called a transceiver, allowing for two-way communication with one device.
The pulses of light carry information in a sophisticated code that was specially devised to maximize the amount of information carried per fiber, encrypt and secure the information from unwanted tampering, and provide routing instructions so the information makes it to the right destination. To code the light, the transceiver can modulate the intensity of the light pulses it injects or even alter the phase of the light wave. The receiver knows how to interpret the code and translate it into a language the computer understands. It’s a little bit like Morse code, but way better and more complicated.
Attenuation
As the light travels down the fiber, various events will cause the intensity of the light, or optical power, to be reduced. This reduction in optical power is called attenuation, and it is one of the most critical parameters that must be controlled to ensure an optical system functions properly. For a dive deeper into attenuation, check out our blog. Several things can cause attenuation. First, impurities in the glass fiber can either absorb the light, converting it to heat, or scatter the light, causing it to escape from the fiber and be absorbed into the surrounding materials. External factors, like bending or straining the fibers, can also cause attenuation.
Limiting attenuation is so important because if the optical signal has lost too much power by the time it makes it to the receiver, then the receiver will not be able to understand the message being sent by the transmitter. This means loss of connection and no Netflix…or worse! There are many other important fiber parameters, but we won’t get into those right now.
Splices and Connectors
The length of fiber optic cable that can practically be manufactured, shipped and installed is limited to a few kilometers or less, so fiber optic connectors and splices are needed to join multiple lengths of cable together so that optical signals can be transmitted farther. Splicing can be either mechanical or via “fusion.” Mechanical splices secure the ends of two fibers together by some mechanical means and precisely align them so that light can pass from one fiber to the other with minimal optical power loss. Usually, they use a special kind of gel that allows the light to pass through the space between fiber ends more efficiently. Fusion splicing, on the other hand, consists of precisely aligning two fibers and then heating them until they melt together, forming one continuous fiber.
While splices are used when a more permanent connection is required, fiber optic connectors exist to provide a means of physical connection that can more easily be disconnected and reconfigured. There are many different types of connectors that are optimized based on factors like fiber type, surface polish, and application. You may find more splices in outside plant backbone cables that are usually intended to be permanent and connectors inside data centers or control hubs where connections are more commonly being reconfigured for various reasons.
Pictured Above: AFL FUSEConnect® Splice-On Connectors
Keep in mind, though, both splices and connectors introduce extra attenuation. Fusion splices result in much lower attenuation than mechanical splices. And either kind of splice will usually result in less attenuation than a connector.
Optical Link
The combined system of transmitter, receiver, fiber, splices and connectors can be called an optical link. Put another way, an optical link is the term used to describe the path through which the light travels. The specific components in each optical link differ from project to project, but the main function of an optical link is to get optical signals from point A to point B. There can be other components included in an optical link, such as regenerators or amplifiers, which boost the optical signal to reach greater distances, or even devices like splitters, couplers and multiplexers, which divide and combine the signals traveling along the fibers.
Active and Passive Components
Components in an optical link can be subdivided into categories of active and passive. Active components are those that require power to operate and which modify the optical signal, usually increasing the optical power in the system. For example, transmitters are active components because they require electricity to function, generating signals and injecting light into the fiber. On the other hand, regular optical fiber is a passive component because it does not require electricity and does not modify the signal. It simply provides a medium through which the light can travel.
Supporting Ecosystem
Beyond the optical link is a whole ecosystem of supporting infrastructure, components and products that make optical communications possible. They house and protect the optical components, ensure the fiber can be installed in a variety of environments, and help users clean or inspect their optical components. These components include the cable, splice closures, pedestals and hand holes, conduit, splice and patch panels, and hardware for aerial cable. There is a variety of installation equipment, from pullers and tensioners to trenching equipment and cable blowing machines. There are fiber strippers, cleavers and splicers.
Pictured Above from Left to Right: AFL's Apex® X-2 Sealed Splice Closure, formed wire deadend and FlexScan® OTDR
Special cleaning supplies and test and inspection equipment. The list goes on, and now is not the time to go into detail about each one! Since they are not transmitting and conducting the light signals, they are not technically part of the optical link, but they are all necessary for ensuring an optical communications system functions properly.
Networks
The purpose of this blog series is to delve deep into the physical composition of optical communications systems, particularly the fiber optic cable. However, it’s important to note that the pieces we have discussed so far are meticulously designed and selected to function within a network. The term network is used to describe a group of devices that are interlinked and all of the infrastructure that interlinks them. The devices could include things like computers, servers, sensors, phones and even air conditioning units and refrigerators. The interlinking infrastructure could include things like fiber optic cables, cell towers, data centers, etc.
Networks can vary widely in size and number of interconnections. Often many smaller networks are connected, forming larger networks. For example, a single building on a university campus has its own Local Area Network (LAN). The single building’s LAN may be linked to other buildings on the campus, forming a Campus Area Network (CAN). The CAN is then part of a Metropolitan Area Network (MAN), consisting of all the interconnections in a larger area, such as a city. And so on from there all the way up to a global network that would include connected devices all around the world, like the internet. It’s also possible for a network to be completely independent from other networks, which we would refer to as a private network.
At a high level, each network has a design and set of rules that ensure that devices on the network communicate efficiently, securely and reliably. The term used for the overall design and rules of a network is network architecture. The network architecture defines how devices on the network are connected (the “topology”), the communications protocols used by the devices (kind of like the language they speak), and even rules about the hardware and software used on the network.
Conclusion
If you’re thinking “ok, but how does all this relate to the electric power industry?” – don’t worry. Communications play a major, albeit unsung, role in ensuring that the lights stay on. In the next entry in this series, we’ll talk about that, as well as how fiber optic communications are playing a critical role in the next evolution of our power system.