Networks today are able to move information back and forth much faster and more efficient than ever before. Fiber-optic cables play a huge role as the highways that keep these networks running. In this article, we will discuss the basics of fiber-optic cables and their role in enabling ultra-broadband networks to address the voice, video, and streaming demands of today’s world.

What is a fiber-optic cable composed of?

Fiber optic-cables consist of multiple layers that are designed to protect the internal fiber strands made from delicate materials such as glass (or plastic). A fiber-optic cable typically consists of:

Outer Jacket: the outer jacket is the outermost layer which is often made with high-density polyethylene material to provide protection for the inner workings of the cable
Strength member: the strength member is placed below the outer jacket to add the tensile strength of the cable
Coating: the coating is applied to protect the glass fiber from mechanical or environmental effects during application
Cladding: the cladding forms the outer layer of the fiber strand and protects light signals from escaping the core
Core: the core is the inner layer of the fiber strand where the light signal travels within. It is extremely thin, roughly as thick as the diameter of a strand of human hair

Because the internet is a global network, fiber optic-cables need to be able to carry telecommunication data between networks located in geographical areas separated over large bodies of water. Cables are often placed in areas such as the ocean floor, putting them at risk of damage from fishing, earthquakes, or even marine life that can bite or tear the cables. As such, deep-sea cables add extra levels of protection to ensure that networks can communicate even thousands of kilometers apart.

How does optical-fiber carry data?

In fiber optics, data is transmitted in the form of light pulses. These data-encoded light signals are beamed across the pathways of optical fibers, using the fibers as a transmission medium to send/receive data between two different networks.

It is important to note that when light enters a different medium (from air to the glass for example), the path of the light wave is often redirected due to a change in velocity. This is known as refraction and is easily observed when sticking an object into a glass of water. Notice how the object looks visually distorted when looking at it behind the glass as shown below:



As the light signal travels through the fiber, the intensity of the light signal must be sustained as much as possible for data transmission to work cleanly. If the light signal is not refracted at the correct angle, much of the light is directed outwards and lost in the cladding instead of traveling through the core.

Optical fibers trap the light within the core by taking advantage of an optical phenomenon called “total internal reflection.” The refractive index (how fast the light travels through the medium) of the inner core is doped to be slightly higher than that of the outer cladding. This creates an angle that allows the light signal to reflectively bounce in a zig-zag fashion as it propagates through the fiber, as shown below:



Taking advantage of this phenomenon, fiber is able to carry data over much longer distances. With the added help of amplifiers and repeaters, optical fibers are able to keep the light signal relatively unscathed, allowing them to transmit data in networks that can be several kilometers or longer.

What are some of the advantages of fiber?

Higher bandwidth
Fiber-based transmission is generally much faster over longer ranges than copper-based transmission. A common misconception is that fiber is faster than copper because it sends signals at the speed of light instead of as electrical waves. It is important to note, however, that light traveling through glass is not quite as fast as light traveling through a vacuum. What makes fiber much faster is that it offers much higher bandwidth capacity.

Fiber-based optics can operate at much higher frequency ranges, offering significantly more channels to utilize. Fiber can also leverage WDM (Wavelength-division multiplexing)-based technology to send multiple light signals over a fiber strand simultaneously. With that advantage, more information at once can be transferred via fiber compared to copper.

Less crosstalk
Fiber also removes many of the bottlenecks that impedes performance for copper. Copper cables are generally more susceptible to crosstalk, which is when unwanted signals transmitted from one channel create undesired effects in another channel. Fiber is less susceptible to receiving crosstalk from other channels, even while running multiple channels simultaneously.

Immunity to electromagnetic interference
Unlike copper, fiber is also immune to electromagnetic interference. Fiber cables are not affected by unwanted, extraneous electrical noise that can interfere with signal integrity in copper cables, slowing down transfer speeds in copper-based networks.

What are some of the drawbacks of fiber?

Prone to bending
Fiber-optic cables can be prone to bending in situations where the cables need to be snaked around confined areas. Smaller bends around the curvature of the fiber are considered micro-bending. Larger scale bending or wrapping of the fiber cable from installation is considered macro-bending. Both types of bending can be problematic, but optical fiber can still operate under total internal reflection in most circumstances.

Higher costs
One of the main drawbacks is that fiber is generally more expensive to implement. Copper has been widely used for a much longer period of time, so the infrastructure to support copper-based systems are mostly in place. With fewer network infrastructures that already have a system in place that supports a fiber-oriented network, the costs to implement fiber is much higher.

Attenuation
Compared to copper, fiber is less susceptible to attenuation, which is the weakening of signal strength over longer distances. Fiber is, however, still vulnerable to attenuation. The weakening of signal strength is caused primarily by absorption or scattering. Absorption is when the light is absorbed and converted into heat. Scattering occurs when the light collides with other molecules from some of the impurities in the transfer medium.

What types of fiber cables are used?

There are two different general types of fiber optic cables: single-mode and multi-mode fiber. Some of the major differences between single-mode (SMF) and multi-mode fiber (MMF) include how many light modes can be propagated through the fiber, the size of the fiber core, the bandwidth offered, the transmission distances supported, as well as the costs of the fiber.

Single-mode fiber
Single-mode fiber is a type of fiber that supports a single light mode and has a much smaller diameter on its core (9 microns) compared to multi-mode fiber. Single-mode fiber also offers much higher bandwidth than multi-mode fiber and can carry signals at longer distances, which makes it more expensive than standard multi-mode fiber. Due to its ability to support signals at longer distances, single-mode fiber works great in long-haul networks. Single-mode fiber is designated with the OS2 specification, with its cable jacket color coded as yellow. OS2 offers 10Gb/s data rates.

Multi-mode fiber
Multi-mode fiber is a type of fiber that supports the propagation of multiple light modes and has much larger diameter sizes from 50 microns to 62.5 microns. Multi-mode fiber has lower bandwidth and is more prone to chromatic dispersion, which weakens signal strength, but its larger core size works great in simplifying network configuration. It supports signals at shorter distances and because it is also significantly cheaper than single-mode fiber, it's a great fit for short-reach, dense networks.

There are also five standards of multi-mode fiber cables: OM1, OM2, OM3, OM4, OM5. Each represent a different generation of multi-mode fiber and its cable jackets are also color coded to indicate what the standard the cable supports. Each generation has brought improved data rate performance. OM1 is orange colored and offers 100Mb/s data rates. OM2 is also orange colored and offers 1Gb/s, OM3 is aqua colored and offers 10Gb/s, OM4 is violet colored and offers 40/100Gb/s, and OM5 is lime green colored and supports SWDM (Short wave division multiplexing) technology to offer even faster data rates.

 

Connect with Axiom

Axiom is a leading provider of third-party upgrades in server and data center hardware. Axiom's BENDnFLEX™ lineup features bend-insensitive multimode fiber cables that deliver OM4 performance with ultra-low insertion loss, ranging from 3dB with BENDnFLEX™ Silver to .1dB with BENDnFLEX™ Platinum. Maximize uptime and optimize performance even under acute bend environments with Axiom’s BENDnFLEX™ high-performance OM4 fiber-optic cables. For more information on Axiom’s fiber-optic cables, please contact an Axiom sales representative or visit our website for more details at https://www.axiomupgrades.com/



 

Sources:
1. https://www.corning.com/optical-communications/worldwide/en/home/products/fiber-optic-cable.html
2 https://archive.nanog.org/meetings/nanog48/presentations/Sunday/RAS_opticalnet_N48.pdf
3 http://www.fibersystems.com/pdf/whitepapers/Basics-of-Fiber-Optics.pdf
4 https://www.corning.com/media/worldwide/coc/documents/Fiber/white-paper/WP1160.pdf
5 https://andcable.com/understanding-fiber-optic-cables-connectors-whitepaper/ Fiber Optics:
6 https://www.thefoa.org/tech/ref/basic/total_internal_reflection.html

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