143Overview of Modeling Techniques for Optical Transmission Systems
electrical
s
ignal
m
ay
n
ot
n
ecessarily
b
e
l
arge
b
ecause
o
f
t
he
po
wer
b
udget
o
f
t
he
t
ransmis-
sion
s
ystem.
T
hus,
t
he
s
ignal
n
eeds
t
o
b
e
a
mplied
b
y
a
p
reamplier.
W
e
h
ave
d
esigned
a
nd
m
odeled
ve
t
ypes
o
f
p
reampliers
w
hich
a
re
t
he
F
ET
h
igh
i
mpedance,
F
ET
t
rans
i
mpedance,
B
JT
h
igh
i
mpedance,
B
JT
t
rans
i
mpedance,
a
nd
H
EMT-matched
n
oise
n
et-
work.
N
oises
s
uch
a
s
s
hot
n
oise,
t
hermal
n
oise,
p
hotodiode
d
ark
c
urrent,
s
urface
l
eakage
c
urrent,
a
nd
c
hannel
r
esistance
n
oise
a
re
m
odeled
a
nd
i
ncluded
i
n
t
he
r
eceiver
m
odeling
b
ecause our task is to model a real practical optical receiver system.
HEMT-matched
n
oise
n
etwork
p
reamplier
i
s
e
specially
m
odeled
f
or
l
ow-noise
b
road-
band
c
ommunication ...