Optical Fiber: Types, Working Principle, Uses & Advantages

Optical Fiber is a flexible and transparent fiber made of drawing glass that is silica or plastic to a diameter slightly more than a human hair (including the outer coating). It helps in transmitting the data in the light form and thus the transmission is much quicker compared to the electrical wires.

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Key Terms: Optical Fiber, Angle of Refraction, Total Internal Reflection, Optical Fiber communication, Critical Angle, Incidence Angle, Electrical Wires, Plastic

Principal of Optical Fiber

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The working principle of optical fiber lies in the fact that when data is to be transmitted through the optical fiber, the first step is to convert the data into an electrical form from the non-electrical form. The high-frequency light waves act as a carrier to this message. The message signal modulates the light source which is maybe a laser or LED. The basic principle of optical fiber depends on the Total Internal Reflection. The light propagates through total internal reflection (TIR) and at the receiving end, this light energy is converted into the electrical form using photosensitive devices such as photodiodes or phototransistors.

Always check that the incidence angle is greater than the critical angle or M1 >M2, then only the ray of light will reflect continuously.

The video below explains this:

Optical Fiber Detailed Video Explanation:

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Components of Optical Fiber

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The main components of an Optical Fiber are listed below,

• Transmitter- The data and the information are encrypted and converted into light signals for transmission purposes.
• Optical Fiber- The light rays propagate through Optical Fiber.
• Optical Receiver- The receiver receives the light rays and decodes the same to get the actual data and information.
• Optical Regenerator- If the data is transmitted at a long distance, then the regenerator is required for undisturbed transmission.

Also Read: Difference Between Analog and Digital Signal

Structure of Optical Fiber

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The structure of an Optical Fiber are listed below,

• Core- the light transmits within the core. 
• Cladding- it is the upper part of the core and is used to give continuous reflection to the light that is passing through the core. And the refraction index of cladding must be less than the core otherwise it will not lead to continuous reflection. If the vice-versa happens then the refraction will take place and it will lead to loss and signal and loss of data.
• Protective Skin (insulator/jacket)- It is only used to protect the fiber optic cable. The mechanical skin should be strong enough to protect the core from getting broken or destroyed. It must possess the capacity to protect the core from external moisture. 
• Dimensions- The length of fiber optic cable is a minimum of 1km long. The diameter of the core is 5mm to 600mm. The diameter of cladding is around 125mm to 750mm and the thickness of the protective skin must be up to the limit that can protect the core from every means of destruction. More the thickness, the more the safety of the core.

Structure of Optical Fiber

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Types of Optical Fiber

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There are mainly two types of optical fibers such as the Step Index Fiber and the Graded Index Fiber that are subdivided into single-mode and multi-mode fibers. These types depend on the index profile. It means what is the refractive index of the core and the cladding materials.

So the main 4 types of optical fibers based on refraction-index are- Single Mode Step Index Fiber, Multi-Mode Step Index Fiber, Single-Mode Graded Index Fiber, Multi-Mode Graded Index Fiber.

Step Index Fiber- In the case of step-index fiber the core is bound by the cladding in two ends. Here we have the core refractive index and throughout the core materials, there is a constant refractive index (M1). The refractive index of the cladding is (M2) which is less than M1. And if the profile of both the M1 and M2 are joined then it will show a structure like a step. So, it is called step-index fiber. 

It is again divided into two types-

1. Single Mode Step Index Fiber- There is only one path of the optical ray. The diameter of optical fiber is very small. So, it only supports only one mode of propagation that passes through the zig-zag path of the Step Index Fiber.
2. Multimode Step Index Fiber-There are many rays traveling through the optical fiber. The core diameter is comparatively large and hence allows many rays to enter the core at one time. Here the critical angle depends on the external or acceptance angle. 

Graded Index fiber- Here the refractive index of the core medium is not constant. It is made of a concentric layer of a different index material. It means the refractive index value is the highest and when it moves away from the center, the value decreases. So, there is a gradation of the core materials. Hence, it is called Graded Index fiber. It has only multimode Graded Index Fiber.

Here, M1>M1’>M1’’>M2

It means if you go away from the axis of the optical fiber, then the refractive index value reduces. And all these values are greater than the M2 (refractive index of the cladding) which means there is a gradation of the core refractive index. 

Note:- It is known that when the ray enters from denser to rarer medium, it changes its path and moves away from the normal. 

Apart from the above two, optical fibers are divided into the following:-

1. Plastic Optical Fibers- It is used for the core surface so that the transmission process is light. 
2. Glass Fibers- Extremely fine glasses are used to make the transmission faster. 

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How does Optical Fiber Work?

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Before understanding how light rays propagate in optical fiber it is very important to understand the Total internal Reflection.

This whole phenomenon takes place in the optical fiber where the light rays propagate with Total Internal Reflection. The core is the denser medium and the cladding is the rarer medium. When the right rays from the core to the cladding portion, the angle Theta is more than the critical angle, then it will come back in the same medium resulting in Total Internal Reflection. If there are no impurities then all the angles within the core will be the same. If any transverse line is crossing it, then the interior angles would be the same. But if the light ray is slanted, then \(\theta\) created inside the optical fiber is very small and it will not come back to the same medium and Total Internal Reflection will not take place. So, it is very important that \(\theta\) angle is more than the Critical angle to give effect to such a combination.

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Advantages of Using Optical Fiber 

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Although Optical fiber is preferred for many reasons, out of all a few five main reasons are listed herein:-

• Lower Transmission Losses- In optical fibers, total internal reflection takes place which leads to low loss of data. Large spacing between the repeaters is also possible when the possibility of data loss is lower. Optical fiber can be used for long-distance communication and the transmission Losses can take place up to 0.2 decibel/km. Negligible transmission Losses in optical fibers are due to material absorption, linear and non-linear scattering, and Fiber bend losses. 
• Huge Bandwidth Potential- Light rays are used as wave carriers. The light rays have a very high frequency. The optical fibers provide a very large bandwidth due to this high-frequency carrier since as the carrier frequency increases, the bandwidth also increases. The bandwidth ranges about 10¹⁴ Hertz. 
• High Flexibility, thin, small-sized, and moderate weight- The diameter of the optical fibers are very small and occupies very little space. These are light-weighted and easy to transport and store. Optical fibers can be used in populated areas so that the fibers can reduce congestion by occupying less space. 
• Electrical Isolation- Optical fibers are made of silica which is insulators. The light rays travel inside the insulating material. Hence, there are fewer chances of electrical shocks, short circuits, and sparking hazards.
• Signal Security- Hacking of signals is not possible. So if someone tries to steal the signals, they can be detected easily. Hence, this system is mostly used in banking, military, and secret missions.
• Cost-effective- It is available at a lower cost compared to the other modes of communication and the encryption process is also easier.
• Less power Consumption- It absorbs less power compared to other modes of communication as it transmits light which is the fastest mode of transmission. 

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Things to Remember

1. Always install special devices to analyze the optical fiber installation.
2. Optical Wire is always better than copper wire
3. Silica is the best mode of insulator.
4. The Jacket of the optical fiber needs to be thick- more thickness leads to more protection of the core.
5. Data should be encrypted in such a manner so that only the receiver can decode the same. 

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