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TOPIC-OPTICAL FIBRE

PHYSICS(2110011)

GUIDED BY:-MEDHA MAM

Anoptical fiber(oroptical fibre) is a flexible, transparent fiber made bydrawingglass (silica) or plastic to a diameter slightly thicker than that of ahuman hair.[1]Optical fibers are used most often as a means to transmit light between the two ends of the fiber and find wide usage infiber-optic communications, where they permit transmission over longer distances and at higherbandwidths(data rates) than wire cables. Fibers are used instead ofmetalwires because signals travel along them with lesser amounts ofloss; in addition, fibers are also immune toelectromagnetic interference, a problem from which metal wires suffer excessively.INTRODUCTION

Immunity to Electromagnetic InterferenceData SecurityNon Conductive CablesEliminating Spark HazardsEase Of InstallationHigh Bandwidth Over Long DistancesADVANTAGES

Total internal reflectionis a phenomenon which occurs when a propagatingwavestrikes a medium boundary at an angle larger than a particularcritical anglewith respect to thenormalto the surface. If therefractive indexis lower on the other side of the boundary and the incident angle is greater than the critical angle, the wave cannot pass through and is entirelyreflected. Thecritical angleis theangle of incidenceabove which the total internal reflection occurs.TOTAL INTERNAL REFLECTION

The Numerical Aperture (NA) is a measure of how much light can be collected by an optical system such as an optical fibre or a microscope lens. The NA is related to the acceptance angle a, which indicates the size of a cone of light that can be accepted by the fibre.

Both numerical aperture and acceptance angle are linked to the refractive index via: NA = naSin a = (n12 n22)1/2Where n1 = refractive index of core n2 = refractive index of cladding na = refractive index of air (1.00) NUMERICAL APETURE AND ACCEPTANCE ANGLE

One way of measuring the NA of this fibre is to fill the fibre with light and measure the characteristics of the light leaving the fibre. Plug the fibre into the analog output and position the components on the optical bench as shown in figure.ascreen

Analog in

BNC & LED Analog out

Photodiode 1Photodiode 2

BNC & LED

Fibre

The fibre output is a cone of light that spreads out wider as the distance from the fibre exit increases. The grid slide or screen and ruler can be used to measure diameters. The edges of the cone of light may appear fuzzy so there will be an error introduced into your measurements.Measurement of the edges is an approximation to the notion of Full Width Half Maximum (FWHM). This is how light boundaries are characterised .

There are 2 types of propagation mode in fiber optics cable which are multi-mode and single-mode. These provide different performance with respect to both attenuation and time dispersion. The single-mode fiber optic cable provides the better performance at a higher cost.

The number of modes in a fiber optic cable depends upon the dimensions of the cable and the variation of the indices of refraction of both core and cladding across the cross section. There are three principal possibilities which are multi-mode step index, single-mode step index and multi-mode graded index.MODES OF PROPAGATION

There are three types of fiber optic cable commonly used: single mode,multimodeand plasticoptical fiber (POF). Transparentglass orplasticfibers which allow light to be guided from one end to the other with minimal loss.TYPES OF OPTICAL FIBERS

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