OPTICAL FIBER AND ITS APPLICATIONS Presented by Dr

OPTICAL FIBER AND ITS APPLICATIONS Presented by Dr. M. LAWRENCE ASSISTANT PROFESSOR DEPARTMENT OF PHYSICS ST. JOSEPH’S COLLEGE(AUTONOMOUS) TIRUCHIRAPPALLI-2

Optical Fiber and its Applications CONTENTS Optical fiber Guiding mechanism Total internal reflection Numerical aperture Types of optical fibers Refractive index mode Applications

Optical fiber An optical fiber is a flexible, transparent fiber made by drawing glass(silica) or plastic to a diameter slightly thicker that of a human hair.

The information carried by the light wave should need a guiding medium through which it can be transmitted safely. The guiding medium is called as optical fiber.

Optical fiber cable A bundle of optical fibers consists of thousands of individual fiber wires as thin as human hair, measuring 0. 004 mm in diameter is known as optical fiber cable.

Guiding mechanism in optical fiber The light which enters from one end of the fiber strikes on the interface of core and cladding at greater angle of incidence. The light beam under goes total internal reflection and it passes along the length of the fiber.

Total internal reflection in optical fiber The optical fiber obeys the laws of reflection and refraction of light waves.

A light ay travelling in a medium of refractive index n 1 incident on another medium of lower refractive index n 2 at the boundary. This light ray is reflected back in to first medium or refracted through second medium. The reflection or refraction of the light at the interface depends on the difference in the speed of light in two materials having different refractive indices and angle of incidence.

Numerical aperture(NA) Used to describe the light gathering or light collecting ability of an optical fiber The numerical aperture(NA) of an optical system is a dimensionless number that characterizes the range over which the system can accept or emit

Types of optical fibers Depending on the number of modes of propagation the optical fiber are classified in to two types (i) single mode fiber (ii) multimode fiber Single mode fiber If only one mode is transmitted through an optical fiber, then the optical fiber is known as single mode fiber. its core diameter is small in the order of a few times the wavelength of light

It is designed to have small refractive index difference between the and cladding. The single mode fiber must be used along with laser diodes It can support only one mode of propagation

Multimode fiber If more than one mode is transmitted through an optical fiber, then the optical fiber is known as multimode fiber.

The large core radii of multimode fiber makes it easier to launch light in to the fiber. It can support a number of modes.

Refractive index profile The refractive index of the core and cladding, the optical fibers are classified in to two types. 1. Step-index fiber 2. Graded-index fiber Step-index fiber In step index fiber, the variation is refractive indices of air, cladding and core vary step by step. Hence, this type of fiber is known as step index fiber.

Step index fiber is classified in to two types. They are (i) Step index -single mode fiber (ii) step index-multi mode fiber Step- index single mode fiber

A step index single mode fiber has a core diameter of 5 to 10 mm and an external diameter of cladding of 50 to 125 mm. Multimode multi mode fiber

A step-index multimode has a core diameter of 50 to 200 mm and an external diameter of cladding 125 to 300 mm It has a core material with uniform refractive index and cladding material of lesser refractive than that of the core Graded index multimode fiber

A graded index multimode fiber has a core diameter of 50 to 200 mm and an external diameter of cladding 100 to 250 mm. The refractive index of the core is maximum at the axis of the fiber and it gradually decreases towards the cladding.

Difference between single mode fiber and multi mode fiber Single mode fiber In single mode fiber, only one mode can propagate through the fiber. It has smaller core dia and the difference between the refractive index of core and cladding is very small. Fabrication is difficult and costly. Multi mode fiber allows a large number of paths or modes for the light rays travelling through it. It has larger core dia and refractive index difference is larger than the single mode fiber. Fabrication is less difficult and not costly.

Applications Filters can be used under sea communication Fibers are used in military applications such as aircrafts, ships, tanks etc Fibers are used in public utility organization like railways, TV transmission etc Fibers are used in LAN systems of offices, industrial, plants and colleges etc Fibers are used in telecommunication such as voice telephones, video phones telegraph services, message services and data network.

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