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level: Optical fibres and dispersion

Questions and Answers List

level questions: Optical fibres and dispersion

QuestionAnswer
What are the two conditions for total internal reflection?Angle of incidince greater than critical angle More optically dense medium to less optically dense medium
What is claddingThe less optically dense/ protective medium surrounding the core of an optical fibre
What is the core in an optical fibreThe centre part of an optical fibre
What is the function of cladding in optical fibresStops signals crossing over from one fibre to another Protects the fibre from scratches which leads to light leakage Causes total internal reflection because the cladding is a higher index than the core
What are the two types of dispersionModal Material/ spectral/ chromatic
Describe what modal dispersion islight travelling in differnt paths/ modes
What is material dispersionThe dispersion of light signals due to differnent colours of light having different frequencies and so travelling at differnt speeds
Name a way to stop material dispersionUsing monochromatic light (One frequency of light)
Name some ways to stop modal dispersion and explain whyMaking the core narrower which reduces the possible differnce in modes the light can take
Define attenuationReduction in intensity as a wave travels through an optical fibre
What is attenuation mesaured in?Decibels
What causes attenuation in optical fibres and explain how each can happenScattering - variation in the composition of the optical fibre/ when light rays hit the cladding at less than the critical angle Absorption - electron may absorb a photon of light Bending losses - Bent too sharply light will hit cladding at less than critical angle
What are the applications of optical fibres?In communications In medical endoscopes
Why is it necessary for the core of an optical fibres to be narrow?Stops light taking differnt paths which stops light takes different times for the journey which stops modal dispersion
What is meant by a coherent fibre bundle?Fibres are in the same formation at the start of the fibre to the end
When light is shone through a slit, explain what the bright and dim patches areLight patches are where the light waves from the slit are interferring constructivly and the dim patches are where the light waves are interferring destructivly
What is monochromatic lightLight of one frequency / colour
What is the result of dispersion on the signal being sentSignal spreads in time/ pulse will blur
What is a mode when descussing optical fibres?A path of light
What is the critical angle?Angle which causes the angle of refelction to be 90 to the normal
How can u reduce pulse broadaningMake the core as narrow as possible to reduce the possible differences in path length of the signal Use of a monochromatic source so the speed of the pulse is constant Use of optical fibre repeaters so that the pulse is regenerated before significant pulse broadening has taken place Use of single-mode fibre to reduce multipath modal dispersion
How can u reducde absorption in optical fibresUse a core which is extremely transparent Use of optical fibre repeaters so that the pulse is regenerated before significant absorption has taken place