The Main Parts of Optical Fibre

Optical fibre is a material that allows light to be transmitted. It consists of a core, cladding and coating (Figure 1).

The core is responsible for carrying the light signal, while the cladding prevents the light from escaping. This makes fibers ideal for data transmission over long distances.

Core

The core of an optical fibre is a cylinder of glass or plastic that guides light energy along the length of the fiber. It’s surrounded by a cladding of a different material with a lower refractive index, typically a medium made from another type of glass or plastic.

The light rays travel down the core in multiple zigzag paths, called modes. The modes are reflected off the cladding surface back into the core, following a process called total internal reflection.

There are two basic types of multimode fiber: step-index and graded index. In step-index fiber, the refractive index of the core changes sharply at the interface with the cladding. This allows a series of different modes to travel in a curved path, which greatly reduces modal dispersion.

In graded-index fiber, the refractive index decreases continuously from the core to the cladding. The resulting curved path also reduces modal dispersion, as high angle rays pass more through the lower-index periphery of the core than the center.

Optical fibres are used for many applications, including transmission of data and power. They are also important for measuring stress and strain in a material.

The core of an optical fibre is the most important part of the fibre, as it determines how much of the signal reaches the other end. The core varies in size and shape, depending on the application requirements.

A core’s diameter is the largest circle that can be scribed about its cladding boundary without overlapping with the cladding itself. It’s measured in microns (a unit of measurement with units of millimeters).

The diameter of a single-mode fiber, which is the most common type used in telecommunication networks, is about 8 microns in diameter. This is because the core is so small that it can accommodate one path of light, reducing the likelihood of overlapping signals and distortion.

The number of modes that can propagate in an optical fibre is determined by the wavelength and the refractive index of the core. These modes can be classified into radiation and guided modes, as shown in Figure 2. Radiation modes carry energy out of the core; these energies are quickly dissipated. Guided modes, on the other hand, transport information and power within the core and along the fiber.

Cladding

Cladding is a layer of material surrounding an optical fibre and is typically made of glass or plastic. It is used to protect the fiber from damage and add strength. It also serves to provide extra protection against shock and is usually applied to a variety of optical fibres from 250 microns to 900 microns in diameter.

Cladding has a higher refractive index than the core material. This allows light to enter the cladding and then be reflected back into the core of the fibre. This process is called Total Internal Reflection (TIR).

A fibre is designed with a core and cladding based on its transmission modes and refractive index profile to meet specific needs. The most important parameters to consider include bandwidth, attenuation, and dispersion.

The core is made from high purity materials to prevent any impurities from absorbing or scattering the light signals that are transmitted through the fibre. This keeps the losses down to a minimum, enabling the light signal to be transferred over a large distance.

In some cases, the core of main parts of optical fibre an optical fibre may be made from a single material, such as silica or Germania. But this is not common in most applications, as the material must be very pure to ensure that the light signal does not be absorbed or scattered.

Some fibers have a cladding that is made from another medium, such as air, with a lower refractive index than the core. This allows light to enter the cladding, and then be reflected back into the core without losing its information.

For example, a step index multimode fiber has a large core that is made of one type of glass, and then a cladding that is another type of glass with a different refractive index. These different paths guide the light rays down the length of the fiber, which is why they are called step index.

On the other hand, a graded index multimode fiber has many layers of glass with a lower refractive index as you go outward from the axis of the core. These multiple pathways allow the light rays to travel down the core much faster than they would otherwise.

End-Fittings

Optical fibre end-fittings are used to align and connect two or more fibers. These can be either adapters or fusion splices, depending on the connection type. In fusion splicing, the ends of two fibers are joined with index matching gel or glue between them. There are a number of different types, including little glass tubes or V-shaped metal clamps.

End-fittings may be crimped to make them permanent and they are the safest of all fittings. They are also commonly used in hydraulic or high pressure applications.

There are many end-fittings available, main parts of optical fibre each with a different function and feature. These include:

Angle-polished connectors are designed to reduce the loss from back reflection. These connectors have the fiber end face polished at an angle so that light that reflects from the interface will not travel back up the fiber and lose signal. This is especially important when using singlemode fiber.

Non-angle-polished connectors have the fiber end face not polished at an angle, and can cause high insertion loss when mated to an angle-polished connector. They are also distinguished by the use of a green strain relief boot or connector body, usually with the addition of /APC (angled physical contact) to the part’s name.

The insertion loss of an end gap will be much higher than the insertion loss of a straight physical contact connector, because air gaps in end-fittings can cause a reflection at the change in refractive index from the glass fiber to the air in the gap. This reflection is called fresnel loss and can have a significant impact on laser based systems.

Aside from minimizing the insertion loss, end-fittings should be polished properly to minimize the loss caused by typical airborne dirt that can scatter and absorb light. The polishing film should be changed regularly.

These end-fittings are made of either PTFE or PEEK and feature UNF threads. They are suitable for connection of 0.8 mm (1/32″) OD tubing to any fluidic module. They are available in a pack of 10 pieces.

End-fittings are a vital part of optical fibre technology. They allow a fiber to be connected to other fibers or to a transmitter or receiver or any other equipment. They are often used for high-speed transmission and in telecom closets, but they may soon become common in all networks.

Termination

Fiber termination is the process of connecting a fibre cable to another device. Any mistakes in this step can cause the network to function unreliably. Therefore, many companies and related products have come out to make this task easier and more accurate.

Termination can take place either by splicing a fiber (also known as pigtail splicing) or by connectorisation. The choice will depend on the type of connector required, the environment in which it is installed and your skill level.

Typically, field termination is the most common method used for terminating bulk fiber cables. However, this method has several disadvantages that you should be aware of before making a decision to use it.

First, this method can be very time consuming and requires a lot of skill to complete. It can also be hazardous.

To help you learn and practice this process, we have developed a series of exercises that will cover the three main methods used to terminate optical fibre: Epoxy Style Connectors, Pre-Polished Style Connectors and Fiber Optic Pigtails.

This section will include the workbook and the VHO tutorials for each of these methods, so that you can work through the exercises with the equipment you have available to you. It is recommended that you complete the exercises for all the components and tools you have access to, as it will help you develop a good understanding of the whole process.

In order to get started, arrange all the materials and tools you will need on your work table. A black mat (black Naugahyde works well) is also helpful, as it makes it easier to see the fiber you are working on.

Next, prepare a clean fiber strand to the length that is specified by the manufacturer of the connector you are using. Once you have this strand ready, strip off the protective coating on the end of the strand and then use a cleaver to cleave it into the connector.

After the strand is in the connector, insert the end of the strand into the rear of the connector until it touches the pre-polished piece of fiber already inside the connector. This will be matched by the index matching gel that is inside the connector and this completes the termination.