A power against time graph showing an input pulse and output pulse in an optic fibre,indicates that the output pulse lasts longer but its amplitude is greatly reduced. Why? If optic fibres are such efficient transmitters the change in shape should be minimal.
The transmission down the wire involves many reflections off the outer surfaces of the wire – therefore, some of the light energy takes a longer path through the fiber than other light energy – this separation widens the shape of the output pulse.
Random variations in angle of bounce tends to widen the pulse – some of the light energy makes a more direct path down the fiber – some of the light energy makes a less direct path down the fiber – the further the pulse travels, the wider the spatial difference between the leading edge of the pulse and the tail end of the pulse.
Since the total energy is constant – this must lead to a reduced amplitude – although total energy is more or less constant.
The transmission down the wire involves many reflections off the outer surfaces of the wire – therefore, some of the light energy takes a longer path through the fiber than other light energy – this separation widens the shape of the output pulse.
Random variations in angle of bounce tends to widen the pulse – some of the light energy makes a more direct path down the fiber – some of the light energy makes a less direct path down the fiber – the further the pulse travels, the wider the spatial difference between the leading edge of the pulse and the tail end of the pulse.
Since the total energy is constant – this must lead to a reduced amplitude – although total energy is more or less constant.
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