# 12: Fibre Optics¶

## Example number 12.1, Page number 26¶

In :
#importing modules
import math
from __future__ import division

#Variable declaration
NA=0.16;   #numerical aperture of fibre
n1=1.45;   #refractive index of core
d=90*10**-6;   #diameter of core(m)
n0=1;   #refractive index of air
lamda=0.9*10**-6;   #wavelength(m)

#Calculation
n2=math.sqrt((n1**2)-(NA**2));   #refractive index of cladding
phi=math.asin(NA/n0);    #acceptance angle(radian)
phi=phi*180/math.pi;   #acceptance angle(degrees)
phid=int(phi);    #acceptance angle(degrees)
t=60*(phi-phid);
phim=int(t);    #acceptance angle(minutes)
phis=60*(t-phim);   #acceptance angle(seconds)
N=4.9*(d*NA/lamda)**2;   #number of nodes propagating through fibre
Nstep=N/2;     #number of nodes propagating through graded index fibre

#Result
print "refractive index of cladding is",round(n2,3)
print "acceptance angle is",phid,"degrees",phim,"minutes",round(phis,2),"seconds"
print "number of nodes propagating through fibre is",N
print "number of nodes propagating through graded index fibre is",int(Nstep)

refractive index of cladding is 1.441
acceptance angle is 9 degrees 12 minutes 24.83 seconds
number of nodes propagating through fibre is 1254.4
number of nodes propagating through graded index fibre is 627


## Example number 12.2, Page number 27¶

In :
#importing modules
import math
from __future__ import division

#Variable declaration
lamda=1*10**-6;   #wavelength of light(m)
n1=1.45;   #refractive index of core
n2=1.448;   #refractive index of cladding
d=6*10**-6;   #diameter of core(m)

#Calculation
NA=math.sqrt((n1**2)-(n2**2));    #numerical aperture
N=4.9*(d*NA/lamda)**2;   #number of nodes propagating through fibre

#Result
print "number of nodes allowed to propagate through fibre is",int(N)
print "it is a single mode fibre"

number of nodes allowed to propagate through fibre is 1
it is a single mode fibre