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OPTICAL FIBRES IN TELECOMMUNICATION

CHAPTER ONE

INTRODUCTION

FIBER OPTICS:-  This is a branch of Optics dealing with the transmission of light through hair – thin, transparent fibers.  LIGHT Signals that enter at one end of a fiber travel through the fiber with very low loss of light, even if the fiber is curved.  A basic fiber – optic systems consists of a transmitting device (which generates the light signal) An optical – fiber cable (which carries the light), and a receiver (which accepts the transmitted light signal) and converts it to an electrical signal.

1.1   HISTORY AND CURRENT RESEARCH

In the early 1950’s Abraham Van Heel of the Delft University of Technology in Netherlands introduced cladding as a way to reduce light loss in glass fibers.  He coated his fingers with plastic.  Even with cladding, however light signals in glass fibers would fade after traveling only a few meters.

In 1967 electrical engineers Charles Kao and George Hockham of Britain’s Standard Telecommunications Labs Speculated that those high losses were due to impurities in the glass that there high losses were due to impurities.  They were correct.  Impurities within the fibers absorbed and scattered light within two decades, engineers solved the impurity problem.  Today, Silica glass fibers of sufficient purity to carry infrared light signals for 100km (62ml) or more without repeater amplification are available.

The development of new Optical techniques will expand the capability of fiber optic systems.  Newly developed of new optical fiber amplifiers, for example, can directly amplify optical signals without first converting them to an electrical signal, speeding up transmission and lowering power requirements.  Dense wave division Multiplexing (DWDM) another new fiber – Optic technique, puts many colours of light spread into a single strand of fiber – optic cable.

Each colour carries a separate data stream.  Using DWDM, a single strand of fiber – Optic cable can carry up to 3 million bits of information per second.  At that rate, downloading the entire contents of the library of congress, a feat requiring 82 years with a dial-up modern, would take just 48 seconds.