Fiber Optic Cables--Introduction, Working Principle and Development

Ⅰ. What is an fiber optic cable?

A fiber optic cable is a component that resembles an electrical cable, but contains one or more optical fibers for the transmission of light. It is mainly composed of optical fiber, plastic protective sleeve and plastic sheath. There are no metals such as gold, silver, copper and aluminum in the fiber optic cable, and generally have no recycling value. It refers to a certain number of optical fibers, which form a cable core in a certain way, and are covered with a sheath and an outer sheath on the outside, and are used to realize a communication line for optical signal transmission.

It were first used in the mid-1970s. In fiber optic cables, light signals are transmitted from light-emitting diodes or semiconductor lasers through thin plastic or glass fibers by internal reflection. Advantages of fiber optic cables over traditional coaxial cables include low material cost, high transmission capacity, low signal attenuation, data security, chemical stability, and immunity to electromagnetic interference. By the end of 2022, the total length of national fiber optic cable lines will reach 59.58 million kilometers. Gigabit optical networks have covered more than 500 million households, and 2.312 million 5G base stations have been built and opened.

Ⅱ. The composition of fiber optic cables

1. Strengthening component

The strengthening component is mainly to withstand the external force added during laying and installation. The configuration methods of fiber optic cable strengthening components are generally divided into "central strengthening components" and "peripheral strengthening components".

Generally, the strengthening component of layer-stranded and skeleton fiber optic cables are located in the center of the cable core and belong to the "central strengthening component" (strengthening core). The strengthening component of the central tube fiber optic cable is moved from the core to the sheath, which belongs to the "peripheral strengthening component". Reinforcement components generally include metallic steel wires and non-metallic fiberglass reinforced plastics (FRP). Non-metallic fiber optic cables using non-metallic strengthening components can effectively resist lightning strikes.

2. Cable core

The cable core consists of single or multiple optical fibers. The cable core structure should meet the following basic requirements:

(1) The strengthening element in the cable core should be able to withstand the allowable tensile force.

(2) The section of the cable core should be as small as possible to reduce the cost. Inside the cable core are optical fibers, sleeve or carcass and strength elements. The cable core also needs to be filled with grease. It has reliable moisture-proof performance to prevent the diffusion of moisture in the cable core.

(3) To make the optical fiber in the best position and state in the cable to ensure stable optical fiber transmission performance. When the fiber optic cable is subjected to certain external forces such as pulling and side pressure, the optical fiber should not be affected by external forces.

3. Sheath

As long as the sheath of the fiber optic cable protects the cabled optical fiber core, it can avoid being damaged by external mechanical force and environment, so that the optical fiber can be adapted to various laying occasions. Therefore, we require the sheath to have the characteristics of pressure resistance, moisture resistance, good temperature characteristics, light weight, chemical corrosion resistance and flame retardancy.

The sheath of the fiber optic cable can be divided into an inner sheath and an outer sheath. The inner sheath is generally made of polyethylene or polyvinyl chloride. The outer sheath can be determined according to the laying conditions, and the LAP outer sheath composed of aluminum tape and polyethylene plus steel wire armor is used.

Ⅲ. How fiber optic cables work?

Optical fibers transmit data in the form of light particles (or photons) that are pulsed through the cable. The glass fiber core and cladding each have a different index of refraction that bends incident light at an angle. When optical signals are sent through a fiber optic cable, they reflect off the core and cladding in a series of zigzag reflections, following a process known as total internal reflection. Due to the denser layer of glass, the light signal does not travel at the speed of light, but travels about 30% slower than the speed of light.

Fiber optic transmissions sometimes require repeaters over long distances in order to renew or boost the signal throughout the transmission. These repeaters regenerate the optical signal by converting the optical signal to an electrical signal, processing the electrical signal, and retransmitting the optical signal.

Ⅳ. The advantages and disadvantages of fiber optic cables

1. Advantages

(1) Due to its light weight, it is very easy to install;

(2) The fiber optic cable is anti-electromagnetic interference;

(3) Its bandwidth is higher than that of copper cables;

(4) It consumes less power and allows long-distance data transmission;

(5) Since the cables are lighter and thinner, they use less area than copper wires;

(6) Fiber optic cables are extremely difficult to tap because they do not generate electromagnetic energy. These fiber optic cables are very secure for transferring data;

(7) Light has the fastest speed in the universe, so the signal speed is faster;

(8) The cable is resistant to most acidic elements that come into contact with copper wire and is inherently flexible.

2. Disadvantages

(1) The cable is very easy to be damaged during installation;

(2) It requires a special device to determine the transmission of the fiber optic cable;

(3) The cables are difficult to merge, so there will be beam loss within the cable;

(4) The installation cost of the fiber optic cable is very high. It requires expensive fusion splicers and trained experts to install the fiber optic cable;

(5) The installation of cables is cost-effective. They are not as strong as wires, so fiber optics usually require special equipment.

Ⅴ. Cable installation skills

1. Test cable

Before and after installation, we need to test the cable to make sure it is working properly. This includes continuity and signal strength testing, as well as any other testing that may be required. Regular cable testing can detect problems early so they can be resolved quickly and efficiently.

2. Plan ahead

Proper planning and preparation are important before starting any fiber optic cable installation. This includes mapping cable routes, identifying potential obstacles, and obtaining necessary permits or approvals. It is also important to consider factors such as the type of cable, connectors and equipment required for the installation. Having a thorough plan in place will ensure a smooth installation process and identify and resolve potential problems before they occur.

Also, we need to do a site survey to make sure there is enough space to install the cables. Also, we check for any underground utilities or other potential hazards. Additionally, we make sure there is a detailed test plan in place to ensure the system works properly. In the long run, proper planning and preparation can save time, money, and potential trouble.

3. Choose the right cable

Fiber optic cables are an essential part of modern telecommunications infrastructure. However, not all fiber optic cables are created equal. Different cables have different properties and are designed for specific use cases. When selecting a cable for a particular application, we consider the environment in which it will be installed.

For example, if the cable is to be installed outdoors, it is important to choose a cable that is suitable for outdoor use. This type of cable typically has a robust sheath that can withstand extremes of temperature, humidity, and other weather conditions. It also resists damage from factors such as UV radiation, water and chemical exposure.

It is also important to consider the temperature rating of the cable. It will be exposed to different temperature ranges, such as cold or hot environments. Cables designed for extreme temperatures will have a higher temperature rating than cables designed for indoor use. In addition, we must also consider the humidity rating of the cable. Fibers in high humidity environments can be exposed to water vapor that can damage the fibers. Therefore, in a high humidity environment, we should choose a cable with a high humidity level.

4. Use the correct stitching technique

Splicing is a critical step in the cable installation process. Improper splicing can result in lost signals and weak connections, which can lead to system failure. Fusion splicing is considered to be one of the most accurate and reliable methods of splicing fiber optic cables. The process involves using heat to fuse, or melt, the ends of two fibers together, creating a permanent connection. This approach ensures low loss and high quality splices, resulting in minimal signal loss and a secure connection. Also, we use proper cutting techniques such as precision cutting before splicing. This can greatly improve the quality of the stitching. It is also important to use proper equipment, such as fusion splicers and cutting knives. In addition, we need to have well-trained operators to ensure the smooth completion of the welding process. In summary, proper splicing techniques, equipment and well-trained operators are essential for safe and reliable connections during fiber optic cable installation.

5. Follow safety guidelines

When installing fiber optic cables, safety should always be a top priority. This includes proper grounding and bonding, taking care to avoid contact with live circuits, etc. We also follow OSHA regulations and guidelines to ensure the safety of installers and any individuals who may come into contact with the cables in the future.

6. Protect the cable

During the installation process, we want to protect the fiber optic cable. This includes using a boot or conduit to protect the cable from damage, and not bending or kinking the cable. Damaged cables can cause serious problems such as loss of signal or complete system failure.

7. Hire Professionals

If we have no experience in fiber optic cable installation, we'd better hire a professional to handle the task. Not only do they have the knowledge and expertise to get the job done right, but they are also able to deal with any unforeseen issues that may arise.

8. Precautions for underground installation

Underground fiber optic cable installation also faces its own set of challenges. This includes identifying the location of buried utilities and taking care not to damage them during installation, etc. To protect cables and components from damage, we need to consider the type of conduit or sheathing required for underground installations.

9. Use the right tools

Having the right tools is critical to successfully installing fiber optic cables. This includes things like fiber optic cutters, strippers and cutters, and any other specialized tools that may be required. Using the correct tools will make the installation process easier and ensure that the cables are properly prepared and connected. It's also important to use high-quality tools. Poor quality tools can damage the fiber optic cable, resulting in poor performance and loss of signal. Using the correct tools also helps reduce the risk of injury during installation. Also, it is important to use the correct tool for the specific type of fiber optic cable being installed. Because different types of fiber may require different tools or procedures.

Ⅵ. Precautions for using fiber optic cables

1. When loading and unloading fiber optic cables, we should use lifting machinery or special platforms.

2. Fiber optic cables cannot be placed flat or overlapped, and must not be subjected to impact, extrusion or any mechanical damage. At the same time, the fiber optic cable should also be protected from moisture and prolonged exposure to the sun.

3. The cable reel with fiber optic cable should not be moved for a long distance. If short-distance rolling is required, we should also roll the fiber optic cable in the direction marked on the cable reel.

Ⅶ. Fiber optic cables failure

1. Fusion splicing failure of fiber optic cable joint construction

In the process of laying fiber optic cables, we often use fiber optic cable fusion splicers to fuse two sections of optical fibers into one. Since the glass fiber in the core layer of the fiber optic cable is fused, we need to use the fusion splicer correctly according to the type of fiber optic cable during the welding process at the construction site. The operation does not conform to the construction specifications and the change of the construction environment will easily cause the fiber to be contaminated with dirt, which will cause impurities to be mixed in the fusion splicing process, resulting in a decrease in the communication quality of the entire link.

2. The fiber optic cable is compressed or broken

This is the most common fault in fiber optic cable faults. The optical fiber is subject to external forces or natural disasters, resulting in tiny irregular bends or even breakage. When a break occurs inside a splice closure or fiber optic cable, we cannot see the break from the outside. However, the refractive index will change at the break point of the fiber, and even reflection loss will be formed, which will deteriorate the quality of the fiber transmission signal. At this point, we use the OTDR fiber optic cable tester to detect the reflection peak to find the bending attenuation or break point inside the optical fiber.

3. Poor polishing of joints

Poor connector polishing is also one of the main failures of fiber optic links. The ideal optical fiber cut plane does not exist in the real physical environment. They all have some undulations or slopes. When the light in the fiber optic cable link encounters such a tangent surface, the diffuse scattering and reflection of light due to the irregular joint surface will greatly increase the attenuation of light. On the curve of the OTDR tester, the attenuation area of the poorly polished cut surface is much larger than that of the normal end surface.

4. Pollution of optical fiber connector

Pollution of pigtail joints and moisture in jumper fibers are the main causes of cable failures, especially in indoor networks where there are many short fibers and various network switching devices. During the operation, excessive dust, insertion loss, finger touch, etc. will easily make the fiber optic connector dirty, which will make the optical path unable to be adjusted or the optical attenuation is too large. We should use alcohol wipes for cleaning.

5. Fiber optic cable routing line length

Due to the physical characteristics of the fiber optic cable itself and the inhomogeneity in the production process, the optical signal propagating in it is being diffused and absorbed all the time. If the fiber optic cable link is too long, the overall attenuation of the optical signal of the entire link will exceed the requirements of network planning. If the attenuation of the optical signal is too large, the communication effect will be reduced.

6. The bending angle of the fiber optic cable is too large

The cable bending attenuation and pressure attenuation are essentially caused by the failure of total reflection in the optical transmission process due to the deformation of the fiber optic cable. Optical fibers have a certain degree of bendability. But when the optical fiber is bent to a certain angle, it will cause a change in the propagation direction of the optical signal in the fiber optic cable, resulting in bending attenuation. This requires us to pay special attention to reserve sufficient angles for the wiring during wiring construction.