An optical fibre communication system (NRZ coding) is operating at a data rate of 20 Mb/s and a bit-error-rate of 10^-9 (at most one error can occur for every 10^9 bits sent). The receiver is a PIN-photodiode operating at a wavelength of 850 nm. The source is a GaAlAs LED that couples 50 μW optical power into a fibre (fibre loss is 3.5 db/km) with a 50 μm core diameter. Connector loss at the source and detector is 1 dB each and the safety/system margin is 6 dB. Determine the maximum transmission path length (link distance).
also how do I find the losses due to the that LED

 

What losses are you referring to? It states there is a 1 dB loss a the interface to the cable.

 

the losses you are referring to are at the connectors
I am referring to the ones due to the LED