Module 15 : ERBIUM DOPED FIBER AMPLIFIERS (EDFA)
Lecture : ERBIUM DOPED FIBER AMPLIFIERS (EDFA)
  Noise Figure :
 

Noise figure is a measure of the quality of amplification. It is defined as the quotient of the signal to noise ratio (SNR) of the input signal to that of the output signal.

$\displaystyle {\rm N.F.}\ = \frac{({\rm SNR})_{input}}{({\rm SNR})_{output}}$

Due to ASE, the output SNR is smaller than that of the input and hence N.F. $ >1$, i.e. an optical amplifier cannot improve the optical signal SNR. Like gain, N.F. is also measured in logarithmic scale

$\displaystyle {\rm N.F. (dB) }\ = 10\log_{10} {\rm N.F.}$
 

The value of N.F. depends on the pump frequency. For large SNR values, an approximate expression for N.F. is given by

$\displaystyle {\rm N.F. } = \frac{1}{G}\left[1+ \frac{2P_{ASE}}{h\nu\Delta}\right]$

where $ P_{ASE}$is the noise power of ASE, $ \nu$is the pump frequency and $ \Delta$the bandwidth of EDFA. The noise figure thus depends both on the pump power and EDFA length.

   
1