# Chapter 18 Fibre Optics¶

## Example 18.1 Page no 859¶

In :
#given
c=3*10**8          #velocity of light
f=4.4*10**14       #frequency of red light
f1=7.0*10**14     #frequency of violet light

#calculation
h1=c/f             #wavelength of red light
h2=c/f1            #wavelength of violet light

#result
print"wavelenght for red= ",round(h1,9),"m"
print"wavelngth for violet= ",round(h2,8),"micron"

wavelenght for red=  6.82e-07 m
wavelngth for violet=  4.3e-07 micron


## Example 18.2 Page no 862¶

In :
#given
n1=1.535             #refractive index of fibre optics

#calculation
import math
x=(n1**2)-(n2**2)
y=math.sqrt(x)     #numerical aperture
z=math.asin(y)*180/3.14      #theta

#result
print"NA = ",round(y,3)
print"(theta)in(max) = ",round(z,1),"degree"

NA =  0.369
(theta)in(max) =  21.7 degree


## Example 18.3 Page no 868¶

In :
#given
w=22                  #spectral width of LED
l=2                   #length of fibre
d=95                  #dispersion value
p=d*w                 #pulse dispersion
pt=p*l                #total pulse dispersion

#result
print"pulse dispersion = ",p,"ps/km"
print"total pulse dispersion = ",pt,"ps/km"

pulse dispersion =  2090 ps/km
total pulse dispersion =  4180 ps/km


## Example 18.4 Page no 885¶

In :
#given
d=30                 #length of fibre cable
l=0.4                #loss

#calculation
T=d*l                #total cable loss

#result
print"total cable loss = ",T,"dB"

total cable loss =  12.0 dB


## Example 18.5 Page no 887¶

In :
#given
b=565                      #Line bit rate of fibre 1
c=3.5                      #Cable dispersion of fibre 1
t=4                        #Transmitter spectral width of fibre 1
b1=1130                    #Line bit rate of fibre 2
c1=3.5                     #Cable dispersion of fibre 2
t1=2                       #Transmitter spectral width of fibre 2
x=440000                   #assumed gaussian constant

#calculation
L1=x/(b*c*t)               #span length in km of fibre 1
L2=x/(b1*c1*t1)            #span length in km of fibre 2

#result
print"span lenght of fibre 1= ",round(L1,2),"Km"
print"span lenght of fibre 2= ",round(L2,2),"Km"

span lenght of fibre 1=  55.63 Km
span lenght of fibre 2=  55.63 Km