# 13: Optical Fibre¶

## Example number 13.1, Page number 250¶

In [2]:
#importing modules
import math
from __future__ import division

#Variable declaration
n1=1.49;                    #refractive index of core

#Calculation
NA=math.sqrt((n1**2)-(n2**2));      #Numerical aperture

#Result
print "The numerical aperture is",round(NA,1)

The numerical aperture is 0.3


## Example number 13.2, Page number 250¶

In [3]:
#importing modules
import math
from __future__ import division

#Variable declaration
NA=0.5;                       #numerical aperture of fibre
n0=1;                         #refractive index of the medium(air)

#Calculation
i=i*180/math.pi;         #angle(degrees)

#Result
print "The acceptance angle is",i,"degrees"

The acceptance angle is 30.0 degrees


## Example number 13.3, Page number 250¶

In [6]:
#importing modules
import math
from __future__ import division

#Variable declaration
NA=0.25;                        #numerical apperture
lamda=0.75;                    #wavelength(micro m)

#Calculation
f=(2*math.pi*a*NA)/lamda;      #normalised frequency
Ng=(f**2)/2;                    #number of guided modes

#Result
print "The number of guided modes is",int(Ng)

The number of guided modes is 1370


## Example number 13.4, Page number 250¶

In [8]:
#importing modules
import math
from __future__ import division

#Variable declaration
pi=100;                 #mean optical power launched(micro m)
po=5;                   #mean optical power at fibre output(micro W)
l=6;                    #length(km)

#Calculation
S=10*math.log10(pi/po);         #signal attenuation(dB)
Sk=S/l;                 #signal attenuation(dB/km)

#Result
print "The signal attenuation is",round(Sk,3),"dB/km"

The signal attenuation is 2.168 dB/km


## Example number 13.5, Page number 250¶

In [10]:
#importing modules
import math
from __future__ import division

#Variable declaration
ns=2.89;                 #sum of refractive indices of core & cladding
nd=0.03;                 #difference of refractive indices of core & cladding

#Calculation
NA=math.sqrt(ns*nd);         #numerical apperture

#Result
print "The numerical apperture for the optical fibre is",round(NA,2)

The numerical apperture for the optical fibre is 0.29


## Example number 13.6, Page number 250¶

In [14]:
#importing modules
import math
from __future__ import division

#Variable declaration
NA=0.28;                  #numerical aperture
lamda=0.8;               #wavelength(micro m)

#Calculation
f=(2*math.pi*a*NA)/lamda;           #normalised frequency
Ng=f**2/2;                           #number of guided modes

#Result
print "The number of guided modes is",int(Ng)
print "answer in the book varies due to rounding off errors"

The number of guided modes is 2176
answer in the book varies due to rounding off errors


## Example number 13.7, Page number 250¶

In [16]:
#importing modules
import math
from __future__ import division

#Variable declaration
S=2;                  #signal attenuation(dB/km)
l=1;                  #length(km)
p0=20;                #mean optical power at fibre output(micro W)

#Calculation
pi=p0*10**(S/10);     #mean optical power launched into fibre(micro W)

#Result
print "The mean optical power launched into a fibre is",round(pi,1),"micro W"

The mean optical power launched into a fibre is 31.7 micro W


## Example number 13.8, Page number 251¶

In [18]:
#importing modules
import math
from __future__ import division

#Variable declaration
S=2.3;                #Signal attenuation(dB/km)
l=4;                  #length(km)

#Calculation
S=S*l;                #signal attenuation for 4km in dB
P=10**(S/10);         #ratio of mean optical power

#Result
print "ratio of mean optical power is",round(P,1)

ratio of mean optical power is 8.3


## Example number 13.9, Page number 251¶

In [20]:
#importing modules
import math
from __future__ import division

#Variable declaration
op=1/4;          #ratio

#Calculation
#S=10*log(pi/po)
S=10*math.log10(1/op);         #signal attenuation(dB)

#Result
print "Signal attenuation is",int(S),"dB"

Signal attenuation is 6 dB