# Chapter 9 :Optical Amplifiers¶

## Example 9.1 , Page no:164¶

In [1]:
import math
from __future__ import division

#initialisation of variables
lambda1=1.3*1e-6;  #wavelength in m
c=3*1e8;  #velocity of light in m/s
SNRoutdB=30;  #signal to noise ratio at outputin dB
SNRout=10**(SNRoutdB/10);  #signal to noise ratio at output normal scale
new=c/lambda1;  #frequency in Hz
h=6.6e-34;  #plancks constant
P=0.5e-3;  #Input power in W
NFdB=4;  #noise figure in dB

#CALCULATIONS
NF=10**(NFdB/10);  #noise figure in normal scale
SNRin=NF*SNRout  #signal to noise ratio at input normal scale
delta_Be=P/(2*h*new*SNRin);  #receiver bandwidth in Hz

#RESULTS
print"Signal to noise ratio at Input=",round(SNRin,5);
print"Reciever bandwidth is=",round(delta_Be/1e14,5),"x10^14Hz";  #division by 1e14 to convert the unit from Hz to 10^14 Hz
print"The answer given in textbook is wrong";

Signal to noise ratio at Input= 2511.88643
Reciever bandwidth is= 0.00653 x10^14Hz
The answer given in textbook is wrong


## Example 9.2 , Page no:164¶

In [2]:
import math
from __future__ import division

#initialisation of variables
PASE=1e-3;  #amplified spontaneous emission power in W
Gdb=20;  #optical amplifier gain in dB
G=10**(Gdb/10);  #optical amplifier gain in normal scale
delta_newbynew=5e-6;  #fractional bandwidth
h=6.6e-34;  #planck's constant

#CALCULATIONS
ns=PASE/((G-1)*h/delta_newbynew);  #noise factor

#RESULTS
print"noise factor is=",round(ns/1e21,5),"x10^21";  #division by 1e21 to convert the unit from Hz to 10^21 Hz
print"The answer given in textbook is wrong";

noise factor is= 76.5228 x10^21
The answer given in textbook is wrong


## Example 9.3 , Page no:165¶

In [3]:
import math
from __future__ import division

#initialisation of variables
L=50;  #link length in Km
Fiber_loss=0.2;  #fiber loss in dB/Km
Req_Gain=Fiber_loss*L;  #required Gain
Fn1db=5;  #Noise figure in dB
Fn2db=5;  #Noise figure in dB
Fn3db=5;  #Noise figure in dB
Fn1=10**(Fn1db/10);  #Noise figure in normal scale for all amplifiers
Fn2=10**(Fn2db/10);  #Noise figure in normal scale for all amplifiers
Fn3=10**(Fn3db/10);  #Noise figure in normal scale for all amplifiers
G1=10**(Req_Gain/10);  #gain in normal scale
G2=10**(Req_Gain/10);  #gain in normal scale

#CALCULATIONS
Fneff=Fn1+(Fn2/G1)+(Fn3/(G1*G2));  #Effective noise figure
SNRindb=30;  #Signal to noise ratio at input in dB
SNRout=10**(SNRindb/10)/Fneff;  #Signal to noise ratio at output in dB
SNRoutdb=10*math.log10(SNRout);

#RESULTS
print"Required Gain=",round(Req_Gain,5);
print"Effective noise figure=",round(Fneff,5);
print"Signal to noise ratio at output =",round(SNRoutdb,5),"dB";

Required Gain= 10.0
Effective noise figure= 3.51013
Signal to noise ratio at output = 24.54677 dB