Fiber-Optic Cable: Construction and Types Available

The world of telecommunications is very quickly changing from copper wire networks to fiber optics. While coaxial cables we use with cell phone signal booster kits (also called Passive Distributed Antenna System) are still the norm because they perform very good under those conditions, fiber technology is a game changer when used with Active Distributed Antenna System (Active DAS). Fiber-optic cables are completely transforming telecommunications and connectivity. Today, signals can be sent across the globe at the speed of light, simply by using fiber optic cables.

What Is a Fiber-Optic Cable and What Is It Used for?

A fiber optic cable is basically a network cable: a cable whereby strands of glass fibers are contained within an insulated casing. Fiber optic cable has been designed specifically for the long-distance transfer of high-performance telecommunications and data networking.

Consisting of one or more strands of glass, about the thickness of human hair, encased in an insulated outer jacket, fiber optic cable provides higher bandwidth than wireless coaxial cable, and is capable of transmitting data over longer distances. These cables are responsible for supporting most of the world's telephone systems, cable television, and Internet.

Using pulses of light generated by light-emitting diodes, or small lasers, the fiber optic cable carries communication signals. In the center of each glass strand is the "core", and the core is surrounded by cladding, a layer of glass that reflects the light inwards, allowing the light to pass through bends in the cable while avoiding loss of signal. It is the core of the cable that provides the pathway for light to travel over long distances. Light pulses are used in fiber-optic cables to send information, as opposed to electrical signals.

How Do We Use Fiber Optic Cables?

The world of network communication has been completely revolutionized by fiber-optic cables, ever since their inception almost 40 years ago. Some of the more obvious uses for fiber optic cable are listed below:

Internet, because fiber optic cables are capable of transmitting huge amounts of data at high speeds. When compared to traditional copper wire, a fiber optic cable is more flexible, lighter, less bulky, and can carry more data.

Telephone, because the use of fiber-optic communication means faster connections and clearer conversations without any lag on either side.

Cable Television, because fiber optic cable has greater speed and bandwidth, making it perfect for transmitting signals for high definition TVs. In addition, when compared to copper wire, the same quantity of fiber optic cable is much cheaper.

Dentistry and Surgery, including Microscopic and Biomedical Research. Fiber-optic cable is widely used in the areas of medicine and research. Nonintrusive surgical methods, also known as endoscopy, require optical communication. In that, a tiny bright light is used to illuminate the surgery area within the body. This makes it possible to reduce both the size and number of incisions.

Computer networking, because networking becomes much easier and faster when using fiber optic cables. Users state that there is a dramatic decrease in the amount of time it takes to transfer information and files across networks when fiber-optic cables are used.

Automotive Industry, where fiber-optic cables are playing a very important safety role in today's modern vehicles. These cables are widely used for exterior and interior lighting of vehicles. And, fiber-optic cables become invaluable in the use of safety applications such as airbags and traction control. The reason for this is the fact that signals can be transmitted between various parts of the vehicle at lightning speed.

Lighting and Decorations, because fiber optic cable provides an economical, simple, and attractive solution to lighting projects, like Christmas trees and other lighting decorations.

Space and Military Applications, because there's an extremely high level of data security required in both aerospace and military applications, and fiber-optic cable provides the ideal solution for data transmission.

Mechanical Inspections, where fiber optic cable is used to inspect difficult-to-reach places, which can include plumbers inspecting pipes and site inspections by engineers.

Who Uses Fiber Optic Cables?

In order to provide a physical connection to a device, or network, fiber-optic cables can simply be plugged into patch panels and communications equipment. They are used exclusively in our Active Distributed Antenna Systems (Active DAS). The fiber optic distribution network connecting mobile service carrier signal lines to antennas and other equipment transmits cellular signals most effectively. Fiber-optic cables are typically used by Governments, commercial businesses, the military, and of course there are many other industrial applications where fiber-optic cable is used in the transmission of data, video, and voice.

Commonly Used Fiber-Optic Terms:

Absorption: The absorbing of light energy in an optical fiber during transmission, caused by natural impurities in the glass. The key reason for signal loss (attenuation) in an optical fiber is absorption and scattering. See below for "scattering".

Attenuation: Caused by absorption and scattering, attenuation is the loss of signal power, or signal strength, during transmission as it passes along a fiber between two points. Attenuation is usually measured per unit length and expressed in dB per kilometer.

Attenuator: A device that induces loss to reduce signal power in a fiber optic link.

Back Reflection: BR (back reflection) occurs typically at connector interfaces where a reflection is caused by a glass-air interface. BR is a term that is applied to any process that causes light in a fiber to change direction and return to the source.

Bandwidth: This is the highest frequency capable of being carried by an analog system. Bandwidth is also the information-carrying capacity of digital systems. It is the range of frequencies a terminal device or fiber-optic waveguide can transmit information or data. Because distance plays an important role, bandwidth is measured in MHz-km and GHz-km.

Buffer: Buffer is a protective layer that is applied directly on the fiber to protect the fiber or cable from physical damage. Fabrication techniques include loose tube buffering, tight jacket buffering, and can also include multiple buffer layers.

Insertion Loss: When a component like a splice or connection point has been inserted into an optical fiber system, the loss caused is known as Total Optical Power Loss.

Loss Budget: The maximum amount of power lost per optical link. Loss Budget can be described as the maximum loss tolerated by a given link.

Multimode: A fiber-optic cable whereby the core diameter is much larger than the single mode waveguide core - 50µm+, compared to 2µm to 9µm, which is why multimode fiber is used instead of single mode fiber for short distance applications. Multimode is an optical fiber which transmits multiple modes of light.

Return Loss: (Optical Return Loss) expressed in units of dB, optical return loss is the ratio of power directed into a cable and the power of light returned via the fiber. Expressed in measurements of positive dB, it is better to have a higher number.

Scattering: Scattering is one of the major causes of attenuation. It occurs when light changes direction after colliding with small particles, causing loss in optical fibers.

Single Mode: An optical fiber (or waveguide) with a small core diameter; the signal travels in one path through its core. Used over long distances for high-speed transmissions, its smaller core makes coupling the light source more difficult. However, it does provide greater bandwidth than multimode. Single mode optical fiber typically has an 8-10 µm core within a 125 µm cladding.

Wavelength: Expressed in microns or nanometres, wavelength is a means of measuring the color of light. Measurements are taken from a point on one wave to the corresponding point on the next wave. Wavelengths are typically 850, 1300, and 1350nm.

Multimode Cable Vs. Single-Mode Cable.

Multimode cable is typically available in two core sizes - 50 µm and 62.5 µm. It has a large diameter core, with multiple pathways of light. This cable is generally used for voice and data fiber applications, like adding on to existing networks, and also in applications like bringing fiber to the desktop and alarm systems. Both core sizes of multimode cable use either laser light sources or LED.

Multimode 50 µm cable should be considered for new installations and constructions because in the 850 nm wavelength it provides higher speeds and longer link lengths than the 62.5 µm cable. This type of cable is recommended for premise applications, such as intra-building, horizontal, and backbone connections.

While single-mode cable has a yellow jacket, multimode cable typically has an aqua or orange jacket. For identification purposes, there are other colors available for a number of applications.

Because single-mode cable has a smaller 8 to 10 µm glass core, it has only one pathway of light passing through. That means that the light is realigned towards the center of the core, unlike with multimode where the light bounces off the edge of the core.

Compared to multimode cable, single-mode cable is capable of providing 50 times more distance. This means that single-mode cable is preferred for high bandwidth applications, as well as long-haul network connections over larger areas. This includes campus backbone applications and cable television. Because single-mode cable delivers higher bandwidth, single-mode fiber strands full duplex can be used with more than double the throughput of multimode fiber.

Construction of Fiber Optic Cable.

A fiber-optic cable is designed to protect the inside fiber core that carries the transmission of a light signal. The construction of a fiber-optic cable includes the fiber core, cladding, primary coating, strength members (or buffer strengthening fibers), and cable jacket.

Core: The fiber core of fiber-optic cable is the central physical medium of the cable that carries the light signal received from an attached light source and delivers it to a receiving device. This core is a continuous hair-thin strand of silica glass or plastic that is measured by the size of its outside diameter. While single mode cores are typically less than 9 µm, the most commonly available multimode sizes of fiber-optic cable are 50 µm and 62.5 µm.

Cladding: The cladding is a thin layer of glass that surrounds the fiber core, forming a single solid glass fiber that is used for light transmission. It creates a boundary containing the light waves, causing refraction. This enables data to travel the length of the fiber segment.

Primary Coating: The primary coating comes after the cladding, and is also known as the primary buffer. It is designed to absorb shocks, provide protection against excessive cable bends, and reinforce the fiber core. This primary coating is basically a layer of plastic which does not interfere with the cladding or the light transmission of the core. These coatings are measured in microns - the buffer is 900 µm and the coating is 250 µm.

Strength Members: Also known as strengthening fibers, these are strands of Kevlar (Aramid yarn) which have been specifically placed to protect the core against excessive tension during installation and other crushing forces.

Cable Jacket: The outer layer of any cable is known as the cable jacket. Depending on the application, some fiber-optic cables have yellow, black, aqua, and other colored jackets. However, fiber-optic cables typically have an orange jacket. Different applications can be designated within a network by using different colors.

Cable Differences:

Comparing Simplex Cable vs. Duplex Patch Cables.

A simplex fiber cable has one single strand of plastic or glass fiber. It is typically used when a multiplex data signal is used or when only one transmit and/or receive line is needed between devices. On other hand, a duplex zipcord fiber cable has two strands of plastic or glass fiber joined with a thin web, and is typically used where a separate transmit and receive are necessary for duplex communication between devices.

Both multimode and single-mode patch cables can be either duplex or simplex, and both duplex zipcord and simplex cables are tight-buffered and jacketed with Kevlar strengthening fibers.

With a simplex fiber-optic cable having only one fiber link, it should be used for applications that require one-way data transfer. For example, an oil line monitor sending oil flow data to a central location, or an interstate trucking scale sending a truck's weight to a monitoring station.

Single-mode fiber-optic cable and duplex multimode cable should be used for applications where simultaneous, bidirectional data transfer is required. Duplex cable is required for hardware applications like workstations, ethernet switches, fiber switches and servers, and backbone ports.

Comparing PVC (Riser) Cable vs. Plenum-Rated Cable

Over the years, PVC cable has become synonymous with riser-rated cable. However, this is not always completely accurate. Riser-rated cable is a subset of PVC cable and not all PVC cable is riser-rated, so care should be taken when using these two terms interchangeably. PVC cable is defined by its outer jacket of polyvinyl chloride which notably emits poisonous vapors if set alight, or even if it becomes overheated.

Riser rated cable is one that has a fire-resistant jacket, while still emitting poisonous vapors if set alight.

Provided the building's ventilation system is a fully functioning, PVC cable can be suitable for both vertical and horizontal runs. Plenum cable can be used as a replacement for PVC. However, the reverse is not true: That is, PVC is unable to be utilized in plenum spaces.

A plenum space within a building is designed for environmental air to move freely. In an office space, for example, an area above the Heating Ventilation and Air Conditioning (HVAC) system, on outer side of the ceiling, is typically a plenum space. Any cable installed in a plenum space must be plenum-rated, which signifies that its jacket is made of such material. For example, Teflon - that it will emit significantly less poisonous vapors than PVC cable, if set alight.

PVC cable is rated Optical Fiber Nonconductive Riser (OFNR) and is unsuitable for use in plenums. OFNR is generally intended for vertical runs between floors as part of a fiber backbone. This type of cable complies with the Underwriters Laboratories (UL) fire safety test Riser/1666. On other hand, Optical Fiber Nonconductive Plenum (OFNP) is generally intended for horizontal runs especially within an air handling conduit. This type of cable complies with the Underwriters Laboratories (UL) fire safety test Plenum/910.

Comparing Distribution-Style Cable vs. Breakout-Style Cable.

Generally quite physically small distribution-style cables are constructed of fibers bundled tightly together within the same jacket. They are then housed and reinforced with either fiberglass or Kevlar. Suitable for conduit runs that are both dry and short, distribution-style cables can be used equally in plenum or riser spaces. While it is possible for the direct termination of fibers within a distribution-style cable, it must be remembered that fibers within the bundle are not reinforced individually, and thus must be terminated inside a cabinet, fiber enclosure, junction box, or patch panel.

Breakout-style cables, on the other hand are a larger, stronger design than distribution-style cables. Suitable for both plenum and riser spaces, breakout-style cables are made up of a bundle of individual simplex cables.

Comparing Loose-Tube Cable vs. Tight-Buffered Cable.

Tight-buffered cables and loose-tube cables are both strengthened in some way, such as with wire strands of stainless steel or Aramid yarn. However, this is where the similarities end, as each has been designed for use in entirely different spaces.

Loose-tube cables are suitable for use in outdoor spaces and are built to withstand harsh weather conditions, including areas of intense humidity. Partly-rigid tubes or protective sleeves protect the cladding, fiber core, and coating, and the fibers themselves are further protected from moisture by way of a water-resistant gel. Contracting and expanding with changes in temperature, loose tube cabling with gel filling will protect against condensation and water, but it is not the ideal choice for an indoor space.

Long indoor runs or LAN/WAN runs of medium length are best served by a tight-buffered cable, which is sturdier than loose-tube cables. With no internal gel or fanout kit for termination or splicing required, tight-buffered cables are simpler to install than loose-tube cables in indoor areas.

Dual Purpose Indoor or Outdoor Cables.

With dry block technology to protect against moisture leakage and buffer tubes filled with gel to stop the migration of moisture, indoor/outdoor cable is perfectly suited for applications in riser spaces, trays, ducks, and aerial spaces. Indoor/ outdoor cable is housed in an outer jacket, with an Aramid yarn overcoat, and a layer of flame retardation protecting the core binder and ripcord.

Interlocking Armored Cable.

Interlocking armored cable is suitable for use just about anywhere. Built to withstand rodents and harsh conditions, interlocking armored cable is rugged and features an aluminum interlocking armored jacket for added protection. Interlocking armored cable doesn't require conduits, saving you money and installation time compared to running fiber cable through innerducts.

For direct burials, outside-plant cable is the ideal solution. Rodent and water resistant, outside-plant cable is built to withstand extreme weather conditions and terminates within 50 feet of the entrance of the building.

Both flexible and lightweight, interlocking armored cable is surprisingly strong and is often the best choice for premise links that are slightly out of the way.

Laser-Optimized 10-Gigabit Cable.

Ideal for building network applications over long distances, laser-optimized 10-gigabit cable is typically aqua colored. This type of cable assembly differs from typical multimode cable assemblies in an important way. Laser-optimized assemblies include a fiber optic cable with a refractive index profile that is graded within each assembly. As a result, the core glass's refractive index reduces towards the outermost cladding, meaning that the light travels faster heading towards the outer side of the fiber than in other directions. Accordingly, the travel time for light paths both long and short is equalized, greatly increasing the accuracy of the transmission and receipt of information over great distances, as much as 300 meters at a speed of 10 Gbps.