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Agilent N4373A Lightwave Component Analyzer, First Edition
∆
----------- -
b
=
2
It is interesting to note that delta voltages and currents are
used as opposed to RMS values. This is done because we
deal with modulation signals in describing lightwave
transducers, where a change in optical power is proportional
to a change in electrical current or voltage.
The overall system forward gain is defined as:
S
=
0
12
Though the overall system gain is defined as an S- parameter,
the individual transfer functions of the E/O and O/E devices
are typically defined in terms of responsivities, because
signals in both the optical and electrical domain are used
and optical signals do not lend themselves conveniently to S-
parameter definitions. Initially, the input impedance of the
E/O converter and the output impedance of the O/E
converter will be assumed to be Z
zero).
R
s
and
R
r
Using the above relationships, we can rewrite S
the transducer responsivities R
V
2
transmitted from O/E device
Z
0
∆
•
=
I
Z
2
0
b
2
(
)
----- - a
S
=
=
0
21
2
a
1
(
no reverse transmission is assumed
(thus S
0
∆
P
0
----------
=
=
E/O source responsivity
∆
I
i
∆
I
2
----------
=
=
O/E receiver responsivity
∆
P
0
and R
s
∆
I
2
-------- -
=
∆
I
1
(
•
∆
)
R
P
r
------------------------- -
=
(
∆
⁄
)
P
R
s
•
=
R
R
s
r
b
2
----- -
S
=
21
a
1
Measurement Concepts
)
and S
are
11
22
in terms of
21
:
r
35
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