Why aren't other electromagnetic waves used in optical fibres instead of visible light? Is it because the wavelength of light fits the internal reflection/refractive index of the material used for the fibre? e.g. Is the material that refracts light cheaper compared to material that refracts EM waves with other wavelengths?
Answer
Almost all fibers (and certainly all telecomms fibers) do not use visible light but infrared light. A typical wavelength used is 1550 nm. At this wavelength the combined effects of absorption and (Rayleigh) scattering in the fiber attains a minimum value, thereby allowing long transmission distances.
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