Optical Fiber Cable and its Types

In this section, we will explain the optical fiber cable and its types. Optical fiber is a buzzing term in modern data communication technology. The optical fiber cable is made up of glass material and has the highest speed data transmission capacity as compared to the other transmission media. In this article, we will explain what is optical fiber cable, its types, how optical fiber works, types of fiber connectors and so on.

What is Optical Fiber

The optical fiber  is a transmission media where signals are allowed to pass through the glass fiber in the form of a light pulse. The fiber is generally made up of a glass or plastic material. Optical fiber consists of core and cladding. The core is the innermost cylinder having a higher refractive index and the cladding is the middle cylinder with a lower refractive index than that of the core. Both the core and cladding is made up of glass and plastic. They are protected by the outer buffer layer.

The main benefit of transmitting a signal in the form of light energy is that the signal can travel faster and covers a greater distance as compared to the copper wire. It is also not affected by external electrical interference and electromagnetic wave.

Composition of Optical Fiber cable

The major constituents of fiber optics are:

• Core
• Cladding
• Buffer coating
• Strengthening fibers
• Outer Jacket

Core

A core is the innermost part of the optical fiber cable. The light rays travel through the core by optical phenomneon called total internal reflection. The refractive index of the core is very high as compared to the cladding. That means the core is optically denser than the cladding. It is made up of glass or plastic material.

Cladding

Cladding is just outside the core and cylindrically surrounds the core. The refractive index of the cladding is less than the core. It is also made up of glass or plastic material.

Buffer Coating

Buffer is a protective coating applied on the outer surface of the cladding. The buffer helps to encapsulate one or more fibers. It provides strength and protects from physical damage and break.

Strengthening Fiber

The strengthening fiber layer is composed of kevlar or wire strands. It protects the core from excessive tension during installation and prevents form physical damage.

Outermost Jacket

The outer jacket encapsulates the whole components of optical fibers. It protects from environmental hazards such as moisture, water, construction equipment etc. It is made up of polyethene or PVC material.

Principle of operation

The optical fiber technology is based on the optical phenomenon known as total internal reflection. The principle of optics defines that when the light travels from the denser medium to the rarer medium, the light rays bend away from the normal. The total internal reflection occurs when the light ray passes from the optically denser medium to the optically rarer medium and the angle of incidence must be greater than the critical angle.

Propagation Modes of optical fiber cable

The optical fiber is categorized into different types according to the mode of light propagation the way the light wave takes the various path to pass through the fiber and the index of refraction variation between the core and the cladding.

• Single-mode fiber 
• Multi-mode fiber

Single-mode fiber (SMF)

• It allows only one mode of light wave to propagate through the fiber.
• The diameter of the core is 8 to 10 micrometres.
• It uses the laser beam as the light source.
• It is used for very long-distance communications.
• Fabrication of single-mode fiber is quite difficult and it is costlier than the multi-mode fiber.

Multimode  fiber (MMF)

• The multimode fibres carry more than one mode of light propagation.
• The diameter of the core ranges from 50 to 100 micrometres.
• The typical size is 62.5 micrometres.
• The different modes of light are passed through the core in different incident angles.
• They are generally used in short-distance communication.
• Fabrication of multimode fiber is easy and the cost is also low as compared to single-mode.
• It uses LED as the source of light waves.

Difference between Single-mode and multi-mode fibers

Multi-mode fibers are further classified into Step Index and graded-index

Step index Fiber

In step-index fiber, the refractive index of the core is uniform and the sharp difference between the core-cladding interface. The light rays pass through the step-index fiber in a zig-zag manner within the core. The step-index fiber can be mono mode or multi-mode.

Characteristics of Step Index

• The refractive index of the core is uniform and then there is a sharp decrease in the refractive index at the core-cladding interface.
• The light waves travel in a zig-zag way within the core.
• The diameter of the core ranges from 50 to 200 microns.

Graded Index Fiber

In graded-index fiber, the refractive index is uniform at the centre of the core but gradually decreases as it approaches the core cladding interface. The light when passed through the graded-index core, it propagates as skew rays or helical rays.

Characteristics of Graded Index

• The Refractive index of the core gradually decreases as it approaches the cladding.
• On the basis of modes, there is only one type of graded index: multi-mode graded index.
• he light waves propagate as skew rays or helical rays.
• The signal distortion is very low.
• The bandwidth of multimode fiber is higher.
• The diameter of the core is 50 micrometre for the multimode graded-index.
• used for long-range communication.

Comparison between Step index and graded index

Fiber Optics Connector Types

The most common types of fiber optics connectors are  LC, SC, ST, FC, and MTRJ connectors. Though all these connectors look different, they have the same functionalities and have the same basic components-coupling device, connector body and ferrules.

SC Connector

• SC stands for subscriber connector.
• Also known as standard connector or square connector.
• It is the most popularly used fiber connector.
• It is a square-type push-pull latch that properly fits into the fibre patch panel with pull-proof stability.
• IT uses a round ferrule size of 2.5mm to hold the fibre.
• It is used in multi-mode as well as single mode.
• It is low cost and most durable.

LC connector

• LC stands for Lucent Connector.
• It is developed by Lucent Technologies.
• Just like the SC connector, it has a push-pull mechanism for proper insertion into the system mounting rack with greater stability.
• It has a split sleeve and cylindrical ferrule.
• The ferrule size is 1.25 mm
• LC connectors are mostly used with SFP  and SFP+ transceivers for high-speed gigabit transmission.

ST Connector

• ST stands  for straight tip
• ST connector has a Boyenet-type mechanism
• It looks similar to the BNC connector used in coaxial cable.
• It was developed by AT&T.
• It has a spring-loaded ferrule size of 2.5mm with a half twist bayonet mechanism for proper insertion.
• It is usually used for short as well as long-distance communication.

FC Connector

• FC stands for ferrule connector.
• It was originally known as a field assembly connector. also known as fibre channel
• It is a fibre connector with a threaded body.
• It is particularly designed for installation in a high-vibration environment.
• It uses a ceramic ferrule with a round screw-type fitment made up of stainless steel.

MTRJ Connector

• MT-RJ stands for Mechanical Transfer Registered Jack
• MT-RJ connectors have endpoints similar to RJ 45 jack.
• It is a duplex fiber connector with both fibers housed in a single polymer ferrule.