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I wanted to know why fiber optics look green or blue, isn't it that it uses total internal reflection, so light shall remain in it? I think may be it's not monochromatic.

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I assume you mean these things: enter image description here

They are lit up by the light source below, which can be any colour. In many of them the source, which is an LED, changes colour over time. The reason why the cables themselves look coloured is that they do not have total internal reflection. Some of the light leaks out through the sides of the cables.

Not having total internal reflection also means they would be useless for transmitting data over long distances: as too much light leaks out, not much ends up at the end of a long cable.

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  • $\begingroup$ link I know when a wave reaches surfaces when material changes some percent of it transmit and remain will reflect back which is used in gpr technology for finding earth layers. is it possible reaching 100 percent reflection in total internal reflection for example in Internet cables or energy leakage is inevitable? $\endgroup$ Commented Sep 16, 2020 at 13:53
  • $\begingroup$ link $\endgroup$ Commented Sep 16, 2020 at 14:01

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