Why in optic fibers, only certain wavelengths (such as 1300,1550) are used? Answer Scattering and absorption are the two enemies of optic fiber. When wavelengh increases, scattering is reduces. That is why they select higher wavelengths ie. 850nm and above But above 850, why they have not chosen 1000,1100,1200,etc. Why they straight away chosen 1300? Because, fiber has minute amounts of water vapour which absorbs certain specific ranges of wavelengths called as WATER BANDS. so we hve to choose wavelengths NOT falling in this range.