# Chapter12 - Fiber-optic communiation systems¶

## Example 12.1 : Page 299¶

In [3]:
from __future__ import division
from math import sqrt, pi
#link length and reise time
af=2.5##dB/km
ac=0.5##dB/splice
nc=1##
lc=1##dB
ncc=2##
plx=-10##dBm
prx=-42##dBm
Ms=6##dB
L=((plx-prx-Ms-(lc*ncc))/(af+ac))##
TTX=12##NS
TRX=11##NS
NS1=3##NS/KM
NS2=1##NS/KM
tmat=(NS1*L)##ns
tint=(NS2*L)##ns
tsys=sqrt((TTX**2+tmat**2+tint**2+TRX**2))##ns
print"maximum possible link length = %0.2f km"% L
print "total rise time of the system in ns is",round(tsys)

maximum possible link length = 8.00 km
total rise time of the system in ns is 30.0


## Example 12.2: Page 305¶

In [4]:
from __future__ import division
from math import sqrt, pi
## link length and bandwidth
print "part (a)"
af=3##dB/km
ac=0.5##dB/splice
nc=1##
lc=1##dB
ncc=1.5##
plx=0##dBm
prx=-25##dBm
Ms=7##dB
L=((plx-prx-Ms-(lc*ncc))/(af+ac))##
TTX=12##NS
TRX=11##NS
NS1=3##NS/KM
NS2=1##NS/KM
tmat=(NS1*L)##ns
tint=(NS2*L)##ns
tsys=sqrt((TTX**2+tmat**2+tint**2+TRX**2))##ns
print "maximum possible link length = %0.2f km"%L
print "part (b)"
af=3##dB/km
ac=0.5##dB/splice
nc=1##
lc=1##dB
ncc=1.5##
plx=-0##dBm
prx=-25##dBm
Ms=7##dB
L=((plx-prx-Ms-(lc*ncc))/(af+ac))##
TTX=1##NS
TRX=5##NS
NS1=9##NS/KM
NS2=2##NS/KM
tf=((NS1*L)**2+(NS2*L)**2)##
tsys=sqrt((TTX**2+tf+TRX**2))##ns
df=0.35/(tsys*10**-3)##
print "system bandwidth = %0.2f MHz"%round(df)

part (a)
maximum possible link length = 4.71 km
part (b)
system bandwidth = 8.00 MHz


## Example 12.3 : Page 310¶

In [5]:
from __future__ import division
from math import sqrt, pi,log10

#no. of subscribers
pt=1##mW
pn=-40##dBm
pn1=10**(pn/10)##
c=0.05##
d=0.11##
x=((pn1)/(pt*c))##
y=((log10(x))/(log10((1-d)*(1-c))))##
n=y+1##
print "no. of subscribers are",round(n)

no. of subscribers are 38.0


## Example 12.4: Page 311¶

In [6]:
# Total power
#given data :
L_eff=20## in km
del_lamdaC=125## in nm
gR=6*10**-14## m/W
A_eff=55*10**-12## in m**2#
del_lamdaS=0.8## in nm
N=32## number of channels
F=0.1##  constant
P_tot=(4*F*del_lamdaC*A_eff)/(gR*del_lamdaS*L_eff*(N-1))#
print "Total power, P_tot = %0.1f mW"%P_tot

Total power, P_tot = 92.4 mW


## Example 12.5 : Page 312¶

In [7]:
#SBS threshold power
#given data :
gb=4*10**-11## in m/W
A_eff=55*10**-12## in m**2
L_eff=20## in km
lamda_p=1.55## micro-m
n=1.46## constant
Va=5960## for the silica fiber in m-s**-1
Vb=(2*n*Va)/lamda_p#
del_v=100*10**6## in Hz
del_Vb=20*10**6## in Hz
b1=1#
b2=2#
P_th=((21*b1*A_eff)/(gb*L_eff))*(1+(del_v/del_Vb))
P_th1=((21*b2*A_eff)/(gb*L_eff))*(1+(del_v/del_Vb))
print "SBS threshold power for the worst case = %0.2f mW"%P_th
print "SBS threshold power for the best possible case = %0.2f mW"%P_th1

SBS threshold power for the worst case = 8.66 mW
SBS threshold power for the best possible case = 17.33 mW