BlogNCERTOptical Fibres and its Types

Optical Fibres and its Types


Optical fibre is a type of data transmission device that works by sending light pulses down a long fibre, which is usually made of plastic or glass. For optical fibre communication transmission, metal cables are chosen because signals move more safely. Optical fibres are unaffected by electromagnetic interference. The fibre optical cable makes use of total internal reflection. Fibre optics, also called fibre optics, is the science of passing light via tiny, transparent fibres to transport data, sound, and images. Fibre optic technology has largely replaced copper wire in long-distance telephone lines and is used to connect computers within local area networks in telecommunications. The fibres are designed to aid in the propagation of light in conjunction with the optical fibre, based on the power and transmission distance requirements. Long-distance transmission is done using single-mode fibre, while shorter distances are done with multimode fibre. The outer wrapping of these fibres requires more protection than metal wires.


A flexible, transparent fibre created by pulling glass (silica) or plastic to a diameter slightly larger than that of a human hair is known as an optical fibre. Optical fibres are most commonly used to convey light between the fibre’s two ends, and they are widely utilized in fibre-optic communications, where they allow transmission over longer distances and at higher bandwidths than wire cables.

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    Fibres are utilized instead of metal wires because signals move through them with less loss; also, fibres are immune to electromagnetic interference, which metal cables suffer from frequently.

    An optical fibre contains a large number of glass components, ranging from a few to several hundred. The fibre cable in this scenario is made out of a cladding layer of glass that surrounds the glass fibre core. The cladding is further protected by a tube called a buffer tube. The jacket layer is the strand’s ultimate layer of protection.

    The core is a small piece of glass at the fibre’s centre through which light is transferred.

    Cladding is a substance that surrounds a glass core on the outside and is known as the outside material. The exterior material reflects light back into the center during normal operation.

    Buffer Coating is a plastic coating that protects the fibres from damage caused by the elements.

    Uses of Optical Fibres

    1. Communication – Fibre-optic cables are used for telephone transmission. Light pulses are transmitted over optical fibres. The technology is comparable to coaxial cable, with the exception that optical fibres can support tens of thousands of simultaneous talks.
    2. Medical applications – Optical fibres are ideally suited to medical applications. They can be produced in ultra-thin, flexible strands that can be inserted into blood arteries, lungs, and other hollow body components. Optical fibres are employed in a variety of tools that allow surgeons to see into the body without requiring surgery.
    3. Simple applications – The most basic application of optical fibres is the transmission of light to regions that would otherwise be inaccessible. Images can also be transmitted using bundles of thousands of very thin fibres assembled perfectly side by side and optically polished at their ends.

    Total Internal Reflection in Optical Fibres

    Because it may be utilized to limit light, total internal reflection is a useful tool. Fibre optics is one of the most common uses of total internal reflection. An optical fibre is a light-transmitting thin, transparent fibre made of glass or plastic. The image depicts the creation of a single optical fibre. An optical fibre’s basic functional structure is made up of an exterior protective cladding and an inner core that transmits light pulses.

    Total internal reflection is possible due to the difference in refractive index between the cladding and the core, just as it is at an air-water surface. If light strikes a cable termination at an angle greater than the critical angle, it is trapped inside the glass strand. As a result, light travels down the length of the cable at a very high speed across a very long distance (tens of kilometres). Optical fibres are widely employed in telecommunications because they allow data to be transmitted across vast distances with little data loss. Endoscopes are another common application in medicine. We can say that fibre optics is a branch of applied science and engineering concerned with the design and application of optical fibres.

    Types of Optical Fibres

    The refractive index, materials utilized, and mode of light propagation all influence the types of optical fibres available.

    The following are the classification based on the refractive index:

    (1) Step Index Fibres: It is made up of a core encased in cladding with a single uniform index of refraction.

    (2) Graded Index Fibres: As the radial distance from the fibre axis rises, the optical fibre’s refractive index falls.

    The following are the categorizations based on the materials used:

    (1) Plastic Optical Fibres: For light transmission, polymethylmethacrylate is employed as the core material.

    (2) Glass Fibres: It is made up of very fine glass fibres.

    The following are the classifications based on the mode of light propagation:

    (1) Single-Mode Fibres: These fibres are used to transmit signals over large distances.

    (2) Multimode Fibres: These fibres are utilized for signal transmission over short distances.

    Four different types of optic fibres are made using the refractive index and mode of propagation of the core:

    (1) Step index-single mode fibres

    (2) Graded index-Single mode fibres

    (3) Step index-Multimode fibres

    (4) Graded index-Multimode fibres

    Working of Optical Fibres

    The total internal reflection concept governs the operation of the optical fibre. Light rays can transport a large amount of data, however, there is a drawback: light rays travel in straight lines. So, exploiting this benefit will be difficult unless we have a long straight cable with no bends. On the other hand, optical cables are designed to bend all light rays inwards (using TIR). Light rays bounce off optical fibre walls and transport data from one end to the other endlessly. Although light signals degrade over distances, depending on the purity of the material utilized, the loss is significantly less than with metal cables.

    • Transmitter: It generates light signals and encodes them for transmission.
    • Optical Fibre: It is the medium used to transfer light pulses (signal).
    • Optical Receiver: It receives or accepts and decodes sent light pulses (signals) to make them usable.
    • Optical Generator: Long-distance data transmission necessitates the use of an optical regenerator.

    Also read: Refraction of Light

    Frequently Asked Questions (FAQs)

    What do you mean by optical fibre?

    Optical fibre is a type of data transmission device that works by sending light pulses down a long fibre, which is usually made of plastic or glass.

    What is the principle behind fibre optical communication?

    The optical fibre communication system is based on the principle of total internal reflection.

    What is the core in the optical fibre?

    The core is said to be the light-carrying portion of the optical fibre.



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