Optical Fiber Communications 4th Edition by Gerd Keiser

Exercise 4

A certain optical fiber has an attenuation of 0.6 dB/km at 1310 nm and 0.3 dB/km at 1550 nm. Suppose the following two optical signals are launched simultaneously into the fiber: an optical power of 150 W at 1310 nm and an optical power of 100 W at 1550 nm. What are the power levels in W of these two signals at ( a ) 8 km and ( b ) 20 km