For multimode fiber, the loss is about 3 dB per km for 850 nm sources, 1 dB per km for 1300 nm. 5 dB/km max per EIA/TIA 568) This roughly translates into a loss of 0. FOA has a online Loss Budget Calculator web page that will calculate the loss budget for your cable plant. There are various causes of fiber optic loss, such as absorption/scattering of light energy by fiber material, bending loss, connector loss, etc. Intrinsic Optical Fiber Losses comprise of absorption loss, dispersion loss and. At TREND Networks, we are frequently asked how much loss is allowed when conducting testing on fibre optic cabling. transmitters which generally don't have e ough power to travel more than 1km.