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Measurement Concepts
Signal Relationships in Opto-electric Devices
34
The LCA measurement technique is built upon concepts used
in characterizing RF and microwave devices. "S- parameter"
or scattering matrix techniques have proven to be convenient
ways to characterize device performance.
The following section will discuss how similar techniques are
used in characterizing devices in the lightwave domain. This
is intended to show the basis on which E/O and O/E
responsivity measurements are defined.
The figure below is a general representation of a lightwave
system, showing input and output signals in terms of
terminal voltages, input and output currents, and optical
modulation power.
S- parameters are used to describe the transmitted and
reflected signal flow within a device or network. For the
model, the following S- parameters are defined:
where:
a
=
1
b
=
1
a
=
2
Agilent N4373A Lightwave Component Analyzer, First Edition
b
1
(
)
----- - a
S
=
=
0
11
2
a
1
b
2
(
)
----- - a
S
=
=
0
22
1
a
2
∆
V
1
----------- -
incident on E/O device
Z
0
∆
•
=
I
Z
1
0
∆
V
1
----------- -
reflected from E/O device
Z
0
∆
V
2
----------- -
incident on O/E device
Z
0
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