Quantum mechanics puts a lower limit of 3 B to the optical noise figure at high optical gain. 980 nm pimping provides a value of 3.1 dB, close to the quantum limit whereas 1.48 m pumping gives a value of 4.2 dB. 980 nm pumping also gives ahigher signal gain, the maximum gain coefficient being 11 dB/mW against 6.3 dB/mW for the 1.48 m pumping. The reason for better performance of 980 nm pumping over the 1.48 m pumping is related to the fact that the former has a narrower absorption spectrum.
References :
E. Desurvire , Erbium Doped Fiber Amplifiers, John Wiley (1994)
Shoichi Sudo (eds.), Optical Fiber Amplifiers : Material, devices and applications, artech House Inc. (1997)
C. R. Pollock, Fundamentals of optoelectronics, Irwin (1995)
m pumping gives a value of 4.2 dB. 980 nm pumping also gives ahigher signal gain, the maximum gain coefficient being 11 dB/mW against 6.3 dB/mW for the 1.48 
m pumping. The reason for better performance of 980 nm pumping over the 1.48 
m pumping is related to the fact that the former has a narrower absorption spectrum.
