Fiber Optic Cable 101: What is It? How It Works? How to Choose the Right Cable?
May 24, 2021
Fiber optic cable is made to meet the specifications performance of optics, mechanical or environment. It is a communication cable which can be used separately or in groups by using one or more optical fibers in the cable as a transmission medium.
The basic structure of fiber optic cable is generally composed of cable core, reinforced steel wire, filler and sheath, and other components such as water blocking layer, buffer layer, insulating metal wire and so on. There is no metal such as gold, silver and in the fiber optic cable, and generally has no recycling value.
Fiber Cable History
In 1976, BELL Research Institute of the United States built the first optical fiber communication experimental system in Atlanta, using 144 fiber optic cables made by Western Electric Company. In 1980, commercial fiber optic cable made of multimode optical fibers began to be used in inter office trunk lines and a few long-distance lines in the city. The commercial fiber optic cable made of single-mode optical fiber began to be used on long-distance lines in 1983. In 1988, the first transatlantic submarine fiber optic cable connecting the United States with Britain and France was successfully laid, and soon the first transatlantic submarine fiber optic cable was built.
In 1978, China developed its own communication fiber optic cable, which adopts multi-mode optical fiber and the core structure is layer stranded. Field tests have been carried out in Shanghai, Beijing and Wuhan. Soon after that, it was used as an inter office trunk line in the local telephone network. After 1984, it was gradually used in long-distance lines and began to use single-mode optical fiber.
Communication fiber optic cable has larger transmission capacity than copper cable, with long distance, small volume, light weight and no electromagnetic interference. Since 1976, it has developed into the backbone of long-distance trunk line, urban trunk line, offshore and cross ocean undersea communication, local area network and private network transmission lines, and began to develop into the field of urban user loop distribution network broadband integrated services digital network provides transmission lines.
Manufacture of Optical Cable
The manufacturing process of fiber optic cable is generally divided into the following processes:
Selection of optical fiber. Select the optical fiber with excellent transmission characteristics and qualified tension.
Dyeing of optical fiber. Standard full chromatogram shall be used for identification, which shall not fade or migrate at high temperature.
Extrusion. Using high elastic modulus and low expansion coefficient plastic to be extruded into a certain size tube, and put the optical fiber into the moisture proof and waterproof filling compound. Then store it for several days (no less than two days).
Stranding. Several extruded optical fiber loose tubes are stranded together with the reinforcing unit.
Outer sheath. Add a layer of sheath to the stranded fiber optic cable core.
The fiber optic cable is composed of three parts: cable core, reinforcing elements and sheath. Two types of cable core structure is single core structure and multi-core structure. For multi-core cable type, we can separate with unitube and stranded loose tube. There are two kinds of reinforced structure as armored and non-armored. Sheath can have different density and material according to the application environment. There are water blocking layer, buffer layer, insulated metal wire and other components as required.
Fiber Cable Type
According to different transmission performance, distance and purpose, fiber optic cable can be divided into user fiber optic cable, local telephone fiber optic cable, long-distance fiber optic cable and submarine fiber optic cable.
According to the different types of optical fiber used in fiber optic cable, it can be divided into single-mode fiber optic cable and multi-mode fiber optic cable.
According to the number of fiber cores in the fiber optic cable, it can be divided into simplex fiber optic cable and duplex fiber optic cable.
According to the different configuration methods of reinforcement, fiber optic cable can be divided into central reinforcement component fiber optic cable, distributed reinforcement component fiber optic cable, sheath reinforcement component fiber optic cable and comprehensive outer sheath fiber optic cable.
According to the different conditions of transmission conductor and medium, fiber optic cable can be divided into all dielectric fiber optic cable, ordinary fiber optic cable and integrated fiber optic cable (mainly used for railway special network communication line).
According to different laying methods, fiber optic cable can be divided into duct fiber optic cable, direct burial fiber optic cable, aerial fiber optic cable and underwater fiber optic cable.
According to different structure, fiber optic cable can be divided into flat cable, layer stranded cable, skeleton cable, armored cable and high density user cable.
The main fiber cable connection type are permanent connection, emergency connection and activity connection.
Permanent optical fiber connection (also called fusion)
In this connection, the connection points of two optical fibers are fusion and connected by means of discharge. It is used in long-distance connection, permanent or semi-permanent fixed connection. Main feature of this connection is that the connection attenuation is the lowest among all the connection types, which typical value is 0.01 ~ 0.03dB/point. But special equipment (welding fusion splicing machine) and professional personnel are needed to operate when connecting, and the connection point also needs special box to protect.
Emergency connection (also called cold melt)
Emergency connection mainly uses mechanical and chemical methods to fix and bond two optical fibers together. The main characteristic of this method is that the connection is fast and reliable, and the typical attenuation of the connection is 0.1 ~ 0.3dB/point. But the long-term use of the connection point will be unstable, and the attenuation will increase greatly, so it can only be used in a short time for emergency.
Mobile connection is a type of connecting stations or stations with fiber cables by using various optical fiber connecting devices (connectors and adapters). This connection type is flexible, simple, convenient and reliable. It is often used in computer network wiring in buildings. The typical attenuation is 1dB / joint.
How to select fiber optic cable
Besides the number of fiber cores and types of optical fiber, the outer sheath shall be selected according to the application environment.
when the outdoor optical cable is buried directly, armored fiber optic cable should be selected. When it’s laid overhead, the cable with two or more reinforcing wire can be selected.
When selecting fiber cables used in buildings, the characteristics of flame retardant, poison and smoke shall be considered. Plenum can be used in the pipeline or forced ventilation areas. Flame retardant, non-toxic and smoke-free (riser cable) is necessary in exposed environment.
Distribution cable can be used in vertically distributed in building. Breakout fiber cable can be used in horizontal cabling.
If the transmission distance is within 2km, multimode fiber optic cable can be selected, and relay or single-mode fiber optic cable can be used for more than 2km.
As the transmission medium of optical fiber communication system, fiber optic cable quality directly affects the entire operation of the communication network. To determine whether a fiber optic cable is good quality, there are different parts we will need to explore, such as optical fibers, outer sheath and strength member, etc. On fiber optic cable quality control and checklists, you can get all details on cable quality.
Tensile and crush limit
The most important thing for long-distance cable laying is to choose a suitable path. The shortest path is not necessarily the best. The land property, possibility of erection or burial should be considered. And when the fiber optic cable turns, its turning radius shall be 20 times larger than the diameter of the fiber optic cable itself.
Aerial Fiber Optic Cable
The method of hanging line is simple and commercial, which is widely used worldwide, but it is time-consuming to add and arrange the fittings.
Overhead way of hanging messenger wire is more stable and less maintenance work. But special winder is needed.
Self-supporting aerial has high requirements for pole, difficult to construct and maintain, and high cost.
Guide device shall be added at the cable lead-up pole when installation, and the cable shall be avoided from dragging. When pulling fiber optic cable, trying to reducing friction. Each pole should be left with a section of fiber optic cable for expansion.
Pay attention to the reliable grounding of metal objects in fiber optic cables. Especially in mountainous areas, high voltage power grid areas and thunderstorm areas, there are usually 3 grounding points per kilometer, and non-metallic fiber optic cables are even used.
Duct Fiber Optic Cable
Before construction, check the occupation of the pipeline, clean and place plastic sub tubes, and put them into the traction line.
The length of layout should be calculated. And enough reserved length must be provided. See the following table for details:Other cable length should be reserved according to design.
The laying length of each time should not be too long (generally 2km), and the pulling shall be conducted from the middle to both sides.
The traction force shall not be greater than 120kg generally. And it should pull the reinforced core part of fiber optic cable. Waterproof protection of the fiber optic cable terminal shall be treated properly.
The cable lead-in and out place must be equipped with a parallel lead device, and it is not allowed to directly drag cable on the ground.
The duct fiber optic cable should also be reliably grounded.
Direct Burial Fiber Optic Cable
The depth of the directly burial fiber optic cable trench shall be excavated according to standards.
Duct can be laid overhead or drilled and embedded where trench cannot be dug.
The bottom of the trench shall be smooth and firm. A part of sand, cement or support can be pre-filled if necessary.
Manual or mechanical traction can be used for laying, but attention shall be paid to the guide and lubrication.
The soil shall be covered and tamped as soon as possible after laying.
Indoor Fiber Optic Cable
When cable laid vertically, special attention should be paid to the load bearing of fiber optic cable. Generally, the fiber optic cable should be fixed once every two floors.
Plastic pipe with protective entrance shall be added when cable passes through wall or floors. The pipe shall be filled with flame retardant filler.
A certain amount of plastic pipes can also be laid in advance in the building. When the fiber optic cable is set to be laid, the fiber optic cable can be installed by traction or vacuum method.
Optical Fiber Detection
The main purpose of optical fiber detection is to ensure the quality of the connection system, reduce the failure factors and find out the fault points in case of failure. There are many methods of detection, which are mainly divided into simple manual measurement and precision instrument measurement.
simple manual measurement
This method is generally used to detect the on-off of optical fiber quickly and to distinguish the fiber during construction. It is realized by a simple light source driving visible light from one end of the fiber and observing which light from the other end. Although this method is simple, it can’t check the attenuation and breakpoint of the fiber quantitatively.
precision instrument measurement
The optical fiber attenuation and joint attenuation can be tested by using optical power meter or OTDR. And even the breakpoint location of optical fiber can be measured. This measurement can be used to quantitatively analyze the causes of the optical fiber network failure and evaluate the quality of products in the network.
After receiving the fiber optic cable, the user shall check the fiber optic cable certificate and the optical data along with the fiber optic cable. Checking the cable drum number, model, core number and length, and check whether the outer package has any damage.
A section of traction rope shall be used to connect with the cable reinforcement when laying the fiber cable. And it will be fixed with cable sleeve or tape with the cable sheath. If it’s duct fiber optic cable, special rotating traction head must be added between the traction rope and the cable reinforcement. Because it is not allowed to pull the outer sheath of the fiber optic cable for traction directly.
For the laying of cables with 2km length or more, it is not allowed to put them from the beginning to the end at one time. The fiber optic cable shall be placed in the middle of the section, and laying with 8-shaped towards both ends
When unloading fiber optic cable from car, It is better to use forklift or crane hoist to place the cable gently on the ground from the vehicle
In field construction, when unloading fiber optic cable from the vehicle, it is advisable to place flat plate between the vehicle platform and the ground, forming a slope of 45 degrees and passing through the middle hole of fiber optic cable drum with a rope. People pull both ends of the rope on the vehicle, and the fiber cable drum is rolling down the slope of the board. It is strictly stacked and horizontally placed when unloading. Dropping optical cable vertically from high place and placing with strong impact on cable to cause damage is forbidden.
When cable drum needed to roll, it shall be rolled in the direction of rotation arrow indicated on cable drum. And long-distance rolling is not allowed.
Single cable drum inspection shall be carried out before construction. Such as the quality of outer sheath and attenuation index
The maximum tensile force of the duct or aerial cable shall not exceed 1500N, and the maximum tension of the direct burial fiber optic cable shall not exceed 3000N.
During construction and layout of fiber optic cable, it is not allowed to bend or form the cable a 90-degree right angle bending. Dynamic bending (such as during construction), for duct and aerial cables, bending radius shall be greater than 20 times of outer diameter of the fiber optic cable. For the directly buried fiber optic cable, the bending radius shall be greater than 25 times the outer cable diameter. When laying took place, the bending radius of the duct and aerial cable shall be greater than 10 times the diameter of this cable. For the directly buried fiber optic cable, the bending radius shall be greater than 12.5 times the cable diameter. Do not bend the fiber optic cable too much to cause a “dead buckle”
The tensile force of fiber optic cable construction shall not exceed the allowable short-term force (duct and aerial cable: 1500N); Direct buried fiber optic cable: 3000N; ADSS fiber optic cable: 20% RTS. And it shall not exceed the allowable long-term force during operation and use (600N for duct and aerial cable, direct buried fiber optic cable 1000N; ADSS fiber optic cable: MAT). The construction of fiber optic cable shall be conducted under the guidance of the corresponding qualified technicians.
It is very important to laying the fiber optic cables according to the correct method. Improper construction will easily cause the increase of attenuation, shorter service life, broken fiber, broken sheath, armor fracture, etc. The cable, especially the feeder cable, is of large diameter and heavy mass. It is necessary to use a bracket to support the cable drum when setting it out. And roll the cable drum while pulling the cable. If it is a loose cable without cable drum, it is necessary to arrange the wiring after it is straightened out. The cable personnel shall be equipped with walkie talkie to keep in touch. To make sure when cable is unable to move, others won’t pull it with brute force. We must continue after fiber cable is being straightened out slowly. This is to ensure that our “fragile” fiber optic cables are safely laid.
Tony Lau is technical manager and co-founder at HOC. He loves writing about content optical fiber communications, specializes in fiber optic cables, FTTH turnkey solutions, ADSS cable, and ODN networks.
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Fiber Optic Cable 101: What is it? How It Works? How to Choose the Right Cable?
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