from math import pi, asin, sqrt
from __future__ import division
#refractive index and bandwidth
#given data :
lamda=1.55*10**-6## in m
del_lamda=1*10**-9## in m
L=320*10**-6## in m
n=(lamda)**2/(2*del_lamda*L)#
Gs=10**(5/10)## 5 dB is equivalent to 3.16
R1=30/100#
R2=R1#
c=3*10**8## in m/s
del_v=(c/(pi*n*L))*asin((1-(Gs*sqrt(R1*R2)))/(sqrt(4*Gs*sqrt(R1*R2))))#
print "refrative index is : %0.2f"%n
print "spectral bandwidth = %0.2f GHz"%(del_v*10**-9)
#bandwidth is calculated wrong in the textbook
from math import log10, exp
#small-signal gain of EDFA and maximum pssible achievable gain
ts=0.80##
sa=4.6444*10**-25##in m**2
n12=6*10**24##m**-3
se=4.644*10**-25##m**2
n21=0.70##
l=7##in meter
x=((sa*n12*l*(((se/sa)+1)*n21-1)))##
G=ts*exp(x)##
Gdb=10*log10(G)##
Gmax=exp(se*n12*l)##
Gmaxdb=10*log10(Gmax)##
print "small signal gain of EDFA = %0.2f dB"%Gdb
print "maximum possible achievable gain = %0.2f dB"%Gmaxdb
from math import log10, exp
#output signal power and overall gain
print "part (a)"
psin=1*10**-6##in watts
ppin=1##in watts
gr=5*10**-14##mW**-1
ap1=60*10**-12##m**2
l=2000##meter
asdb=0.15##dB/km
As=3.39*10**-5##m**-1
apdb=0.20##db/km
ap=4.50*10**-5##m**-1
z=(1-exp(-ap*l))/ap##
y=(gr/ap1)##
y1=z*y##
y2=y1-(As*l)##
psl=psin*exp(y2)##
print "output signal power for forward pumping = %0.2f micro Watt"%(psl*10**6)
print "part (b)"
y1=z*y##
y2=y1-(As*l)##
psl=psin*exp(y2)##
gfra=psl/(psin)##
Gdb=10*log10(gfra)##
print "overall gain = %0.2f dB"%Gdb