Return Loss Measurement
Getting Started With Return Loss
134
Agilent 8163A Lightwave Multimeter, Agilent 8164A Lightwave Measurement
System, & Agilent 8166A Lightwave Multichannel System, Fourth Edition
What is Insertion Loss ?
Light that is absorbed, scattered, or reflected by a component also affects how
much light a component transmits.
The transmission factor for a component is a measure of how much light the
component transmits. It is a ratio of the power transmitted by the device to the
power incident on the device. More normally we talk about the Insertion Loss of a
component. The insertion loss has units of dB. Insertion Loss is given by:
Insertion Loss can be measured in several ways. A description of the method used
by the HP 81534A follows.
How to Choose a Light Source
Highly accurate return loss measurement requires that you use a light source with
a subset of the following properties:
•
low coherence,
•
high power, and
•
power stability.
We recommend that you use any of the following laser sources as part of your
return loss measurement setup:
•
Agilent 83438A Erbium ASE Source, this source offers a high-power low-
coherence output that is very stable over time,
•
Laser Source modules, see
for a list of modules
that can be installed in your mainframe, see the note below that explains use
with highly coherent light sources,
•
Tunable Lasers, see
for a list of modules that can
be installed in your mainframe, the when you want to measure Return Loss
over a wavelength range, see the note below that explains use with highly
coherent light sources, and
•
LED sources, the intensity of the output of LED sources is very stable over
time, although the low-power output of LEDs restricts the dynamic range of
return loss measurement.
N O T E
If you use high-coherence light sources, you can improve performance by:
•
modulating the output signal at 2 kHz or higher or
•
using coherence control to reduce the coherence of the signal.
Insertion Loss dB
(
)
10
Transmission Factor
(
)
dB
(
)
log
–
=
Insertion Loss dB
(
)
10
Transmitted Power
Incident Power
----------------------------------------------------
dB
(
)
log
–
=
or
