Basic Components of a Fiber Optic Cable

Basic Components of a Fiber Optic Cable

Written by Ben Hamlitsch, trueCABLE Technical and Product Innovation Manager RCDD, FOI

What are fiber optic cables made of? A fiber optic cable consists of five basic components: the core, the cladding, the coating, the strengthening fibers, and the cable jacket.

When searching for a fiber optic cable, we need to pay attention not only to the connectors, such as SC to ST fiber cable, LC to SC fiber patch cable, or SC to SC patch cable, but also to the cable itself. There are also several different options available for fiber optic cables, such as LC to LC multimode duplex fiber optic patch cable and LC to LC single mode duplex fiber optic patch cable.

What are the parts of a fiber optic cable?

In most cases, a fiber optic cable will have five primary components: the core, which is responsible for transporting the light signals; the cladding, which surrounds the core with a lower refractive index and contains the light; the coating, which serves to protect the core; the fiber optic strength member; and the cable jacket. This article will provide a detailed introduction to the parts of a fiber cable.

Picture of fiber optic components

What is the Fiber Optic Core?

The fiber optic cable core is the physical glass medium that transports optical signals from an attached light source to a receiving device. The light is transported along the optical fiber via its smallest and most crucial component, which is called the core. The core of an optical fiber is most often constructed of glass, though there are some that are made of plastic as well. The glass that is utilized in the core is exceptionally pure silicon dioxide (SiO2), a substance that is so transparent that you would have the same experience staring through 5 miles of it as you would if you were looking through a window in a house.

Depending on their intended use, cores of optical fibers can be used in a range of applications. The size of the core is different for different types of fiber optics. The typical thickness of a glass core can range anywhere from 8-10 um (microns) for single-mode and 62.5-50 um for multimode; these core sizes are the most prevalent ones utilized in the telecommunications industry. There are primarily two categories of optical fiber: single-mode fiber and multimode fiber, which can be distinguished by the diameter of their cores. Light travels at a single wavelength toward the center of the core of a single-mode fiber, which has a core that is between 8-10 microns in diameter, typically 9 microns for single-mode fiber. Light in a multimode cable travels in multiple paths down the fiber and bounces between the core and cladding as it travels down the core. The core of multimode fiber can be either 50 microns (most common) or 62.5 microns in diameter.

hand drawn photo of fiber optic core sizing

What is the Fiber Optic Cable Cladding?

This is a thin layer that is extruded over the core and serves as the boundary that contains the light waves (more on this later), enabling data to travel through the length of the fiber.

Cladding is what surrounds the core of an optical fiber and has a lower refractive index than the core. This allows the optical fiber to function.

When glass cladding is utilized, both the cladding and the core are produced simultaneously from a silicon dioxide-based material in a permanently fused state. This process occurs when the glass cladding is applied.

During the manufacturing process, various quantities of dopants are added to the core and the cladding to keep the difference in refractive indices at around 1%. At a wavelength of 1300nm (nanometer), a typical core might have a refractive index of 1.49, while the cladding might have a refractive index of 1.47. These quantities, on the other hand, change depending on the wavelength. At different wavelengths, the core of the same fiber will have a different refractive index than the rest of the fiber.

The cladding is also produced in conventional diameters throughout the manufacturing process. 125 micrometers and 140 micrometers are two popular sizes. The core size of a 125um cladding normally ranges from 9m to 50m, and a 62.5m core is typical of a 140um cladding.

upclose shot of of hand drawn fiber optic cladding

What is the Fiber Optic Coating?

The actual protective layer of the optical fiber is the coating. It prevents the cladding from being damaged by shocks, nicks, scratches, and even dampness by acting as a shock absorber. Without the coating, an optical fiber is extremely susceptible to damage. The bending of the optical fiber could create even a single, microscopic puncture in the cladding that would cause the fiber to break. Glass fibers of any kind absolutely must be coated, and you won't be able to buy them without the coating. The ability of the optical fiber to transmit light is not affected in any way by the coating. In most cases, the covering has an outer diameter of either 250 or 900 microns. In most cases, the coating has no discernible hue. It may be colored in some applications so that it can be easily identified.

A specific kind of performance or environment led to the decision to go with this particular coating. Acrylate is a form of coating that is quite common. Typically, two layers of this coating are applied to the surface. The primary coating is put on by brushing it straight onto the cladding. This coating is gentle, and because of this, it acts as a cushion for the optical fiber whenever it is bent. The first coating is somewhat soft in comparison to the secondary coating, which results in a tougher exterior.


the different layers of fiber optic cable

What are the Strengthening Fibers?

Aramid yarn is utilized in fiber optic cables as a tensile strength member, which implies that it contributes to preventing the cable from stretching or breaking when it is subjected to tension. In addition to this, it can be utilized to provide further protection against being crushed, bent, or twisted. Because it is both flame resistant and self-extinguishing, aramid yarn can also be utilized as a component of fire protection.

In the construction of fiber optic cables, aramid yarn is typically combined with other types of materials, such as jacketing material, which serves to shield the cable from moisture and other environmental factors. As well as an outer protective layer of steel or aluminum, which serves to shield the cable from additional mechanical damage.

A wide variety of other applications make use of aramid yarn in addition to its use in fiber optic cables. These other applications include clothing that is resistant to being cut and ballistic-rated body armor, as well as ropes and cables for use in industrial and marine applications, and reinforcement for composite materials used in the aerospace and automotive industries.

In fiber optic cables, aramid yarn plays an important role because it protects the fragile optical fibers that are contained within the cable from damage caused by mechanical stress.

Because it offers both mechanical and thermal protection for the optical fibers that are included within a fiber optic cable, aramid yarn plays a significant role in the overall process of guaranteeing the dependable and secure operation of fiber optic cables.


the strength member of a fiber optic cable


What is the Fiber Optic Cable Jacket?

The protective jackets that are placed around fiber optic cables are extremely important in preventing the fragile fibers that are contained within the cable from being damaged by outside forces and elements. The following is a list of the various types of jackets that can be found in fiber optic cables:

Plenum: Plenum-rated jackets are composed of a material that is resistant to fire and are used in air-handling zones like ceilings and walls.

Riser: Riser-rated jackets are meant to be fire-resistant and are used in vertical cable runs between floors. These lines are referred to as risers.

LSZH: Low smoke, zero halogen jackets are made of a flame-retardant material that, when burned, creates very little smoke and no harmful halogen vapors. 

Outdoor: Jackets that are approved for use in outdoor environments are constructed to endure severe weather conditions, and to protect against moisture and ultraviolet radiation. Outdoor applications, such as buried or aerial cable lines, are among the most prevalent places you'll find fiber optic cables installed.


up-close shot of the fiber optic cable jacket


The environment, building codes, and regulations, each require a different sort of jacket, each of which possesses its own unique set of qualities and standards, and is employed in a distinct set of applications.

In summary, the core, cladding, coating, strength member Aramid yarn, and cable jacket are the five fiber optic components that are present for a fiber optic cable. The coating protects the fiber from damage, the Aramid yarn provides mechanical strength, and the cable jacket protects the fiber from the environment. The core is the central part of the fiber that carries the light signal. The cladding surrounds the core and reflects the light signal back into the core. The strength member, Aramid yarn, provides mechanical strength. The coating protects the fiber from damage. These components, when combined, work together to ensure that data transmission across extensive distances is both efficient and dependable. It is impossible to overestimate the significance of these fiber optic cable components, given that they play an indispensable part in ensuring that modern fiber optic communication systems can operate as intended.

trueCABLE offers a line of bulk fiber optic cables in multimode and singlemode options.



trueCABLE presents the information on our website, including the “Cable Academy” blog and live chat support, as a service to our customers and other visitors to our website subject to our website terms and conditions. While the information on this website is about data networking and electrical issues, it is not professional advice and any reliance on such material is at your own risk.

    1 out of ...