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Fiber Optic Cable: Overview, Types and Application

In the highly connected world of today, the rapid transfer of massive amounts of information has become a priority for all industries. Decades ago, copper wires are the default media for data transmission, but now fiber optic cables have become the golden standard for network cabling for their unparalleled performance and the ability to send data without attenuation. They are designed for fast-speed data networking, and now are frequently used in SMBs, IP security camera systems, data centers, etc.

Fiber Optic Cable

A fiber optic cable is composed of five elements: core, cladding, coating, strengthening fibers and cable jacket. The core is the center of the fiber cable, the medium where optical signals are transmitted. It’s consisted of continuous strands of glass or plastic, whose diameter is measured in microns. The cladding is the layer that protects the core and serves as the boundary that traps the light waves. The coating is a plastic layer that surrounds the cladding, which helps to strengthen the fiber core, helps absorb shocks, and provides extra protection against excessive bending of the cable. The strengthening fibers are used to protect the fiber core from crushing forces during the installation, and the materials can range from Kevlar to gel-filled sleeves. Lastly, the cable jacket is the outer layer of the fiber cable to protect the cable from environmental hazards. 

How do Fiber Optic Cables Work?

Fiber optics use light instead of electrical signals to transmit data. Light (laser or LED) travels down a fiber optic cable by repeatedly bouncing off the ‘walls’ of the cable with continued internal mirror-like reflection. The size of the fiber core is critical in determining how far a signal can travel. In general, the smaller the core, the farther the light will travel before it needs to be regenerated. Since most fiber networks cannot directly blend into the network infrastructure your home or office can use, the stretch between the main fiber network line and the end-user, also known as the ‘last mile’, is often completed by the old-fashioned coaxial cable, copper cable, etc. 

Types of Fiber Optic Cables

There are many types of fiber optic cables. For example, depending on the communication channel, they can be divided into the simplex, half duplex and full duplex types. In this part, we will introduce the most common fiber optic cables in the market. 

Single-mode Fiber Optic Cable

The single-mode fiber optic cable has a 125μm thick cladding around a very small fiber core (9μm), which allows only one spread of the light beam to pass, making it more suitable for long-distance applications. It has very low propagation loss and just no dispersion. Its extremely thin core allows the laser to move in it with almost no reflection, which greatly reduces the attenuation rate. The single-mode fiber optic cable is often covered with a yellow jacket. It can be used in metropolitan networks, small to medium-sized enterprises, campuses, etc., and is typically used for CATV, Internet and telephone applications where the signals are carried using single-mode fibers wound into a bundle.

Multi-mode Fiber Optic Cable

The multi-mode fiber optic cable has a much broader internal core (either 50μm or 62.5μm). It allows multiple modes of light to propagate through the cable and carry multiple streams of data simultaneously. The multi-mode fiber optic cable is usually coated with an orange or aqua jacket, used in short-distance applications like data centers, sensing systems, radio telecommunications, etc. Multi-mode fiber optic cable is less expensive than single-mode fiber and it’s easier to maintain and install. However, the larger core diameter also means greater reflection and signal attenuation.  

Simplex Fiber Optic Cable

Simplex and duplex fiber optic cables feature two different types of communication channels. In the simplex fiber, data only travels in one direction at a time. Simplex cable uses a single strand of fiber with a transmitter (TX) on one end and a receiver (RX) on the other. The cable is not reversible and supports only one-way transmission. Simplex fiber is a great option for setting up a network that will require data to travel long distances in one direction. It’s a good choice for applications like oil line monitors, interstate trucking scales, automated speed and boundary sensors, etc. 

Duplex Fiber Optic Cable

In the duplex fiber cable, the transmission is bidirectional for it uses 2 fibers to communicate. One strand transmits data from point A to point B and the other from B to A. Both ends have a transmitter and a receiver. The duplex fiber optic cable can also be further categorized into half-duplex and full-duplex. Half-duplex means that information can be transmitted in both directions but not simultaneously, while full-duplex means that data transfer can occur in both directions at the same time. It can be utilized in applications, such as telecommunications, workstations, large modems and network servers, and backbone ports.

Single or Multi-Strand Fiber Optic Cable

Single-strand optical fiber cable uses a single strand of optic fiber to send data in two directions, i.e. bi-directional (BiDi) transmission. It greatly increases network capacity by using only one strand of fiber to transmit and receive data, which also reduces failure points. Multi-strand fiber is similar to twin-strand fiber. It has strands of optical fiber to transmit data in one direction, and a similar number of optical fibers to support data transmission in the opposite direction. And multi-strand fiber can support data rates over 25G and be used with MPO/MTP connectors.

Aerial Fiber Optic Cable

Aerial fiber optic cables are usually used for outdoor installation. They are often installed on poles, towers, or other structures above the ground or in rural or suburban areas where it is impractical or too expensive to bury cables underground. The aerial fiber optic cables can resist wind, rain, ice, heat, UV rays and other constant weather changes that vary with the seasons and even throughout the day. According to the installation methods, aerial fiber optic cables can be generally divided into two types: Catenary and self-supporting. Catenary wire or loose tube aerial cables are the most frequently used design in outdoor settings, and you can use them for ducts and lashed aerial installations. But if the installation doesn’t have an existing messenger wire, you can go for the self-supporting type. And within this category, there are three different types of aerial fiber optic cables: ADSS, Figure 8 and OPGW.

Direct Burial Fiber Optic Cable

The direct burial fiber optic cables can be directly buried underground without conduits (usually 1-2 meters deep). They do not require any kind of additional protective covers to be buried directly into the ground. They can be exposed to harsh environmental conditions such as changes in temperature and humidity of the soil. Compared with underground fiber optic cables with conduits, direct burial fiber cables are more solid. They have a built-in conduit that helps them withstand pressure, dust, and even rodent chewing. 

How to Install Fiber Optic Cables?

Proper installation of your fiber optic cables will ensure the best functioning of your system. In this section, we will introduce several ways to install your fiber cables. 

Conduit Installation

Conduit is used when installing underground fiber optic cable to protect the fiber from damage. To install multiple fibers at a time, you can use the inner duct conduit which contains multiple smaller tubes inside of a larger conduit. But when pulling the fiber cable through the conduit, you should lubricate it first. The lubricant helps reduce the pulling load and the chance of breakage during the installation, but it has to be compatible with the cable jacket. For long cable runs, the pulling is often done with special equipment to minimize bends and breakage during the installation. Moreover, to ease the installation, fish tapes should always be placed in the conduit.

Indoor Cable Installation

The indoor fiber optic cable is usually installed in a conduit or a tray. The cable tray is designed to protect and route the fiber optic cables. But one of the concerns when installing fiber cables with cable trays is to avoid any cutting edges and sharp bends All bends must have smooth curves. When a fiber cable is pulled into a conduit or cable tray, the conduit’s bending radius must be larger than the cable’s minimum bending radius. 

Vertical Cable Installation

Cables installed in trays are not subject to any tension. However, for vertical running, a careful design must be made to minimize the tensile forces. Longer vertical wires must be clamped at midpoints to avoid excessive strain on the cable. The clamping force should be applied to the length of the cable as possible. Cable holders can be used at the top of the vertical riser or at the mid-point if frequent clamping is not possible. 

Aerial Cable Installation

Aerial cable installation is very complicated and time-consuming. First, you need to carry out a route survey and ensure the way is free of obstacles like trees. And also you need to gain permission from the property owners or local authorities before the installation starts. Once all the preparation is done, you can decide whether to install the cable using stationary or moving reels. The first method is generally used when the cable is installed above the existing lateral cable and other obstructions. The moving reel method can be used where the cable reel trailer or aerial can move along the pole line and there are no obstacles preventing the lifting of the cable. It is a one-time operation that does not require the use of pull wires, so the installation is usually faster. 

Other Tips on Fiber Optic Cable Installation

• Run the cable in the pattern of Figure 8 to reduce cable twist.

• Never pull on the fiber directly. Pull on the strengthening member (Kevlar) or the pulling eye instead to protect the fiber from breakage.

• Ducts should be sized to meet present and future cable installation requirements. And after the cable is pulled, end plugs should be installed to provide an effective water seal.

• Install vertical, unfilled, loose tube cables with loops to prevent the fiber from slipping.

• On the run<100m, pull the cable directly, but when the length exceeds 100m, use proper lubricants and pull the cable from the middle out to both ends.

• When a messenger wire is used for aerial installation, avoid zigzagging the messenger wire from one pole side to the other.

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