Getting Started With Return Loss
Return Loss Measurement
Agilent 8163A Lightwave Multimeter, Agilent 8164A Lightwave Measurement System, & Agilent 8166A Lightwave
Multichannel System, Fourth Edition
133
Getting Started With Return
Loss
What is Return Loss ?
When light travels through an optical component, most of it passes through, or
into, the component, and some light is absorbed, scattered, or reflected by the
component. In many applications the reflections are unwanted, because they can
affect the emission characteristics of any laser in the system. In such applications,
it is important to measure the reflections for the components of the system.
The reflection factor for a component is a measure of how much light the
component reflects. It is a ratio of the power reflected by the device to the power
incident on the device. More normally we talk about the return loss of a
component. The return loss has units of dB. Return loss is given by:
Return loss can be measured in several ways. A description of the method used by
the HP 81534A follows.
The method used requires the following equipment:
•
a Laser Source module with a stable output,
•
a Power Meter, and
•
a HP 81534A Return Loss module.
A typical setup of the HP 81534A Return Loss module is described in Figure 85.
The description starts with measuring the reflection factor. When we have got this
figure, we can convert it easily to the return loss.
Return Loss dB
(
)
10
Reflection Factor
(
)
dB
(
)
log
–
=
Return Loss dB
(
)
10
Reflected Power
Incident Power
---------------------------------------------
dB
(
)
log
–
=
or
Figure 85
Return Loss Equipment
HP 81534A
Reflection-free
Termination
External
Sensor
A
B
D
C
Coupler
DUT
Laser Source
