A campus data link uses an LED transmitter at 850 nm launching dBm into a multimode…
PHYSICS · Subjective · Fermi University Physics · Optics & Photonics · Beams, resonators and guided-wave photonics · Beams, resonators and guided-wave photonics
Optics and Photonics, Ch Optical fibres in communication and endoscopy
Problem
A campus data link uses an LED transmitter at 850 nm launching −6 dBm into a multimode fibre whose attenuation at this wavelength is 3.0 dB km−1. The receiver's minimum detectable power is −20 dBm (a power in dBm is 10log10 of the power in milliwatts, so the difference of two dBm figures is a power ratio in decibels). Estimate the greatest unrepeated length of this fibre the link can use, assuming attenuation is the only loss in the budget.