# Chapter 14 : Optical fiber measurements¶

## Example 14.1, page 912¶

In [4]:
import math

#Variable declaration
v2=10.7                                   #increased voltage
v1=2.1                                    #voltage
l1=2                                      #length in Km
l2=0.002                                  #length in Km

#Calculation
a=(10/(l1-l2))*math.log10(v2/v1)           #Attenuation
u=0.2/(l1-l2)                              #incertainty

#Result
print'Attenuation per Km = %.1f dB Km^-1'%a
print'Uncertainty = ± %.1f dB'%u

Attenuation per Km = 3.5 dB Km^-1
Uncertainty = ± 0.1 dB


## Example 14.2, page 917¶

In [6]:
import math

#Variable declaration
t2=100                                     #time in sec
t1=10                                      #time in sec
ti=0.525                                   #micro voltage
to=0.021                                   #micro voltage
C=1.64*10**4                               #thermal capacity
tin=4.3*10**-4                             #maximum temperature rise
pop=98*10**-3                              #optical power

#Calculation
tc=(t2-t1)/(math.log(ti)-math.log(to))       #time constant for the calorimeter
a=(C*tin)/(pop*tc)                           #absortion loss

#Result
print'Absorption loss in dB = %.1f dB Km^-1'%a

Absorption loss in dB = 2.6 dB Km^-1


## Example 14.3, page 919¶

In [8]:
import math

#Variable declaration
Vsc=6.14*10**-9                              #voltage
Vop=153.38*10**-6                            #voltage without scattering
l=2.92                                       #length of fibre in cm

#Calculation
a=4.343*10**5*Vsc/(l*Vop)                    #scattering loss

#Result
print'Scattering loss in dB = %.1f dB Km^-1'%a

Scattering loss in dB = 6.0 dB Km^-1


## Example 14.4, page 922¶

In [12]:
import math

#Variable declaration
t1=12.6*10**-9                               #time in sec
t2=0.3*10**-9                                #time in sec

#Calculation
Bop=0.44/t                                 #bandwidth length product

#Result
print'(a) 3dB pulse broadening = %.1f ns km^-1'%(t*10**9)
print'(b) Fiber bandwidth–length product = %.1f MHz km'%(Bop*10**-6)

(a) 3dB pulse broadening = 10.5 ns km^-1
(b) Fiber bandwidth–length product = 41.9 MHz km


## Example 14.5, page 940¶

In [2]:
import math

#Variable declaration
A=6.2                                     #output pattern size
D=10                                    #screen position

#Calculation
NA=A/math.sqrt(A**2+(4*D**2))            #numerical aperture

#Result
print'Numerical aperture = %.2f'%NA

Numerical aperture = 0.30


## Example 14.6, page 942¶

In [1]:
#Variable declaration
phi=4                                       #angular velocity
l=0.1                                       #length in meter

#Calculation
d=we*s                                    #fibre diameter

#Result
print'Outer fibre diameter = %.1f um'%(d*10**6)

Outer fibre diameter = 120.0 um


## Example 14.7, page 950¶

In [35]:
import math

#Variable declaration
a=5*10**-3                                     #optical signal power
b=20*10**-6                                    #optical signal power
c=0.3*10**-3                                   #optical signal power
d=800*10**-9                                   #optical signal power

#Calculation
bdb=10*math.log10(b*10**3)                         #in dBm
cdb=10*math.log10(c*10**6)                         #in dBu
ddb=10*math.log10(d*10**6)                         #in dBu

#Result
print'(a) For a 1 mW reference power level'
print' optical signal power of 5 mW = %.2f dBm'%adb
print' optical signal power of 20 uW = %.2f dBm'%bdb
print'\n(b) For a 1 μW reference power level'
print' optical signal power of 0.3 mW = %.2f dBu'%cdb      #value given in a textbook is incorrect
print' optical signal power of 800 nW = %.2f dBu'%ddb

(a) For a 1 mW reference power level
optical signal power of 5 mW = 6.99 dBm
optical signal power of 20 uW = -16.99 dBm

(b) For a 1 μW reference power level
optical signal power of 0.3 mW = 24.77 dBu
optical signal power of 800 nW = -0.97 dBu


## Example 14.8, page 953¶

In [19]:
import math

#Variable declaration
NA=0.02                               #numerical aperture
yr=0.7*10**-3                        #Rayleigh scattering coefficient
c=2.998*10**8                        #speed of light
wo=50*10**-9                         #pulse time
n1=1.5

#Calculation
p=0.5*(((NA**2)*yr*wo*c)/(4*(n1**3)))       #power ratio
pdb=10*math.log10(p*10**3)                  #in dB

#Result
print'Power ratio  = %.3f X 10^-7'%(p*10**7)     #value given in a textbook is incorrect
print'Power ratio in dB = %.1f dB'%pdb            #value given in a textbook is incorrect

Power ratio  = 1.555 X 10^-7
Power ratio in dB = -38.1 dB