# Chapter 13: Optical fiber systems 2: coherent and phase-modulated¶

## Example 13.1, page 832¶

In [5]:
#Variable declaration
f1=150*10**6                            #reciever IF
f2=19*10**9                             #output frequency change

#Calculation
m=f1*f2**-1                             #maximum tempreture change

#Result
print'Maximum tempreture change = %d × 10^-3 °C '%round(m*10**3)

Maximum tempreture change = 8 × 10^-3 °C


## Example 13.2, page 834¶

In [1]:
import math

#Variable declaration
p=-85.45/10
n=0.86                                       #quantum efficiency
sn=10**-1.2                                  #SNR
h=6.626*10**-34                             #plancks constant
c=2.998*10**8                               #velocity of light

#Calculation
ps=10**(p)                                 #incoming signal power in dB
B=(n*ps*sn*h1)/(h*c)                       #Bandwidth

#Result
print'Incoming signal power, Ps = %f nW'%(ps*10**9)
print'Operating bandwidth, B = %.1f GHz'%(B*10**-9)

Incoming signal power, Ps = 2.851018 nW
Operating bandwidth, B = 1.2 GHz


## Example 13.3, page 878¶

In [8]:
#Variable declaration
pe=4.24                             #probability error function
pe2=20                              #probability exponential function

#Calculation
Np=pe**2*4                           #no of photons
Np2=pe2*4
Np3=pe**2/2

#Result
print'(a) ASK heterodyne synchronous detection = %d photons'%round(Np)
print'(b) ASK heterodyne asynchronous detection = %d photons'%round(Np2)
print'(c) pSK homodyne  detection = %d photons'%round(Np3)

(a) ASK heterodyne synchronous detection = 72 photons
(b) ASK heterodyne asynchronous detection = 80 photons
(c) pSK homodyne  detection = 9 photons


## Example 13.4, page 881¶

In [16]:
import math

#Variable declaration
h1=6.626*10**-34                     #plancks constant
c=2.998*10**8                        #speed of light
Bt=400*10**6                         #FSK signal bit rate
h=1.55*10**-6                        #wavelength

#Calculation
ps=(36*h1*c*Bt)/(h)                #optical power

#Result
print'Minimum incoming optical power level = %.1f nW'%(ps*10**9)

Minimum incoming optical power level = 1.8 nW


## Example 13.5, page 883¶

In [37]:
import math

#Variable declaration
Np=36                                     #average photons
Np2=9                                     #average photons
h=6.63*10**-34                            #plancks constant
f=3*10**8                                 #frequency
Bt=50*10**6                               #bit rates
Bt2=10**9                                 #bit rates
h1=1.55*10**-6                            #operating wavelength
a=0.2                                     #connector loss

#Calculation
Ps=Np*h*f*Bt/h1                           #in watt
Ps1=10*math.log10(Ps*10**3)               #in dB
ma=4-Ps1                                  #Max. system margin
mar=ma/a                                  #Max. repeater spacing

Ps2=Np*h*f*Bt2/h1                         #in watt
Ps3=10*math.log10(Ps2*10**3)              #in dB
ma1=4-Ps3                                 #Max. system margin
mar1=ma1/a                                #Max. repeater spacing

Ps4=Np2*h*f*Bt/h1                         #in watt
Ps5=10*math.log10(Ps4*10**3)              #in dB
ma2=4-Ps5                                 #Max. system margin
mar2=ma2/a                                #Max. repeater spacing

Ps6=Np2*h*f*Bt2/h1                        #in watt
Ps7=10*math.log10(Ps6*10**3)              #in dB
ma3=4-Ps7                                 #Max. system margin
mar3=ma3/a                                #Max. repeater spacing

#Result
print'(a)Max. repeater spacing (50 Mbit s^-1) = %.1f km'%round(mar)
print'                         (1 Gbit s^-1) = %.1f km'%round(mar1)
print'\n(b)Max. repeater spacing (50 Mbit s^-1) = %.1f km'%round(mar2)
print'                         (1 Gbit s^-1) = %.1f km'%round(mar3)

(a)Max. repeater spacing (50 Mbit s^-1) = 352.0 km
(1 Gbit s^-1) = 287.0 km

(b)Max. repeater spacing (50 Mbit s^-1) = 382.0 km
(1 Gbit s^-1) = 317.0 km


## Example 13.6, page 888¶

In [26]:
import math

#Variable declaration
np=150
h1=6.626*10**-34                     #plancks constant
c=2.998*10**8                        #speed of light
bf=20*10**12                         #optical bandwidth
h=1.3*10**-6                         #wavelength

#Calculation
tx=(np*h1*c*bf)/h                    #transmitter power

#Result
print'Minimum transmitter power = %.1f mW' %(tx*1000)

Minimum transmitter power = 0.5 mW