# Chapter 11 :Fiber Optic Communication System Design¶

## Example 11.1 , Page no:191¶

In :
import math
from __future__ import division

#initialisation of variables
BW=7;  #bandwidth in MHz
SNR=60;  #signal to noise ratio in dB
Pin=0;  #Launched power in dBm
Trise_source=20;  #risetime at source LED in ns
delta_lambda=20;  #spectra width in nm
lambda1=850;  #operating wavelength in nm
c=2.998*10**5;  #velocity of light in Km/sec
R=0.3;  #Detector PIN FET responsivity in A/W
Cdiode=3;  #diode capacitance in pf
trise_detector=1;  #risetime at detector in ns
S=-30;  #sensitivity in dbm
Lsplice=0.2;  #splice loss in dB/connector
NA=0.2;  #numerical aperture for GI/MM
n1=1.46;  #refractive index of core
A=2;  #attenuation in dB/Km
Ls=3;  #loss due to source in dB
Ld=1;  #loss due to detector in dB
Psm=5;  #system margin in dB
c=3*10**8;  #velocity of light in m/s

#CALCULATIONS
Available_power=Pin-S;  #available power in dB
Total_loss=Ls+Ld+Psm;
Power_left=Available_power-Total_loss;  #power left in dB
L=(Power_left+Lsplice)/(Lsplice/2+2);
tmod=L*10**3*(NA**2)/(2*c*n1);  #modal dispersion in s
Bit_rate=1/tmod;  #bit rate in bps

#RESULTS
print"Maximum permissible link length is =",round(L,5),"Km";
print"Maximum permissible bit rate is =",round(Bit_rate/10**6,5),"Mbps";  #division by 10^6 to convert the unit from bps to Mbps
print"the answer is different because of rounding off ";

Maximum permissible link length is = 10.09524 Km
Maximum permissible bit rate is = 2.16934 Mbps
the answer is different because of rounding off


## Example 11.2 , Page no:193¶

In :
import math
from __future__ import division

#initialisation of variables
BW=7;  #bandwidth in MHz
SNR=60;  #signal to noise ratio in dB
Pin=0;  #Launched power in dBm
Trise_source=4;  #risetime at source LED in ns
delta_lambda=1;  #spectra width in nm
lambda1=1300;  #operating wavelength in nm
c=2.998*10**5;  #velocity of light in Km/sec
R=0.3;  #Detector PIN FET responsivity in A/W
Cdiode=3;  #diode capacitance in pf
trise_detector=5;  #risetime at detector in ns
F=2.1;  #amplifier noise figure in dB
Camp=2;  #amplifier capacitance in pf
L=2;  #minimum link length in Km
Lsplice=0.5;  #splice loss in dB/connector
NA=0.22;  #numerical aperture for GI/MM
BWGI=600;  #GI/MM fiber bandwidth in MHz F3dB_optical
Te=630;  #temperate in Kelvin
K=(1.38064852 *10)-23;  #boltzman constant in m2 kg s-2 K-1

#CALCULATIONS
SbyN=10**(SNR/10);  #SNR in normal scale
L1=Pmin1/0.2;  #power budget limited link length in Km
Trise_required=(0.35/BW)*10**3;  #Bandwith budgetting rise time required is rise time required in ns//multiplication by 10^3 to convert msec to ns
#for GI
f3dB_electrical=0.71*BWGI;  #3dB elctrical BW in MHzKm
t_intra_modal=1;  #intra modal dispersion in ns/Km
t_inter_modal=3;  #intermodal dispersion in ns/Km
t_fiber_GI=math.sqrt(t_intra_modal**2+t_inter_modal**2);  #rise time of fiber in ns/Km

Maximum permissible link length is = 223.08248 fKm