6. A Raman amplifier is pumped in the backward direction using 1 W of power. Find the output power when a 1-mW signal is injected into the 5-km-long amplifier. Assume losses of 0.2 and 0.25 dB/km at the signal and pump wavelengths, respectively, Aeff = 50 mm2, and gR = 6 10 14 m/W. Neglect gain saturation.