Optical Fibres

Optical fibre consists of a core(thin glass centre) which is surrounded by a cladding layer with a lower refractive index than that of the core to reflect the light back to the core. The optical fibre is surrounded at the outer layer by the buffer coating which is a plastic coating that protects the fibre from damage and moisture. Two …

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Light Attenuation

The attenuation of light refers to the reduction in it’s intensity as it travels through a medium due to absorption or scattering of photons. Primary causes: photoelectric effect, Compton scattering and pair production(for photon energies above 1.022 MeV)   Light travelling in transparent materials is attenuated according to: $I = I_{o} \, e^{- \mu x}$, where I and Io are …

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Measure Of Birefringence

Measure Of Birefringence The birefringence of a material is characterized by the birefringence magnitude or measure of birefringence, which is he difference in the indices of refraction. $\Delta n = n_{e} – n_{o}$, where ne is the refractive indices for light travelling in the parallel direction to the optic axis, no is the refractive indices for light travelling in the …

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Ways Of Exploiting Polarisation

When a polariser and analyser are mounted in the ‘crossed’ position, no light is normally transmitted through the combination. But, if a birefringent crystal is inserted between the ‘crossed’ polarisers, some light is transmitted. Some materials such as glass and various plastics become birefringent when subjected to mechanical stress. This is the basis of photoelasticity. Stresses in pieces of engineering …

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Circular Polarisation

Circular Polarisation Electric field of the circular polarized light rotates but magnitude remains constant. Produced from the superposition of two waves that have the same amplitude and wavelength and are polarized in two perpendicular planes with a phase difference of 90 degrees between them. Circular polarization by quarter waveplate A quarter waveplate is made of a type of birefringent material …

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Polarisation

An ordinary light source consists of a large number of randomly oriented atomic emitters. Each excited atom radiates a polarized wavetrain for roughly $10^{-8}$ s. New wave trains are constantly emitted and the overall polarization changes rapidly in a completely unpredictable fashion. Therefore natural light should not be called unpolarized light. It should be randomly polarized light. A polarizer is …

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Transmittance And Reflectance

By conservation of energy, light energy incident on a dielectric (any transparent or translucent material) will automatically be equal to the sum of the amount of energy reflected and the amount of energy entering the medium. Note: We cannot assume that the energy passing through is the same as the energy entering the medium as there will be scattering and …

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