What is the structure of fiber optic cable?

The simplest fiber optic cable is generally composed of four parts: core, cladding, coating, strength member, and jacket.



A fiber optic cable features a core in the center, which is designed to transport light. The cladding is a thin layer that helps transmit data through the fiber. There is also a coating over the cladding to give further protection for the fiber core. The strength member, also known as strengthening fibers, is usually made of steel, fiberglass, or aramid yarn to keep the fiber core from damage, especially during the installation. The exterior part of the fiber optic cable is called the cable jacket, which is designed to protect the cable from environmental damage.

In addition, the outer jacket is often color-coded to identify the type of fiber optic cable. This is the basic structure of fiber optic cable, but it can feature different structures according to different types.

Types of Optical Fiber Cables

Optical fiber cables can be divided into different types according to different structures, materials, applications, and transmission methods.

Single Mode vs Multimode Fiber

Single-mode fiber (SMF), also known as fundamental or mono-mode fiber, features only one transmission mode as it has a relatively small diametral core. Multimode fiber features a large diametral core that allows multiple modes of light to pass through.



Compared to single-mode fiber, multimode fiber is more cost-effective and suitable for a short distance such as data transmission in LANs. Single-mode fiber has less light reflection when the light passes through the core, so it allows the signal to go further. Single-mode fiber is greater for long-distance applications such as colleges and even the submarine network.

Single-mode fiber can often be divided into OS1 and OS2, while multimode fiber is usually classified into OM1, OM2, OM3, OM4, and OM5. There are different color codes for different kinds of optic fibers, and you can refer to the following chart.



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4- Sub Units

When a Tight Buffer cable has more than two tight buffer fibers gathered as units, and each fiber unit has its own jacket and can be separated as a cable, it is called a "Breakout" cable. Differently, if a cable has fibers that do not have separated jackets and each one cannot be used as cable on its own, it is called a Cord cable or a Distribution cable. Breakout cables are usually used for on premises networks were a fiber cable has to be branched into multiple cables for different zones. Cord cables are used to connect from one point to another, whether they have few fibers and are used within buildings or they have large numbers of fibers and are used in broadband FTTX network infrastructure.







Finally, network infrastructure, which has fiber optic cables as its core element is constantly changing and improving. Thanks to research and development, there can be more and new properties and improvements in fiber optic cables' construction, and we will try to provide more info about them when they are presented.

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An optical fiber cable consists of three primary components:
The Core:

Analogous to the heart of the cable, the core represents the central region where light pulses travel. It's an incredibly slender thread, akin to a strand of human hair, made from materials with a high refractive index. This core is the path through which light signals are guided. For widely used 250um fiber, the diameter of core is around 9um.
The Cladding:

Surrounding the core is the cladding, acting as an optical boundary. Crafted from a material with a slightly lower refractive index than the core, the cladding's purpose is to contain the light within the core through total internal reflection. This reflective mechanism ensures minimal signal loss over distance. The core and clad together makes the diameter of 125um.
The Coating:

Adding a protective layer, the primary and secondary coating envelops the cladding and core. This outermost layer guards the delicate core and cladding against mechanical stress and environmental factors. The coating is designed to absorb shocks, prevent moisture ingress, and safeguard the integrity of the light transmission pathway. Over diameter of the fiber at this stage is around 250um

Collectively, this intricate architecture operates in synergy. When light is induced into the core, it undergoes controlled reflections off the cladding, effectively 'bouncing' within the core due to the differing refractive indices. This phenomenon enables high-speed, long-distance data transmission with minimal attenuation. Now, the question is why are fiber optic cables used? Let's find out!