Agilent Technologies 8163B, Manual, Page: 167 / 466

Getting Started With Return Loss Return Loss Measurement
Agilent 8163A/B, 8164A/B & 8166A/B Mainframes, Sixth Edition
167
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 length
• high power
• [and, for the 81534A, power stability.]
If a return loss module with at least one internal source (such as the
Agilent 81611A, 81612A or 81613A) is not available, we recommend that
you use any of the following 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 “Accessories” on page 319 for a list of modules that can be installed in
your mainframe. Refer to the note below that explains the use of highly
coherent light sources.
• Tunable Lasers, when you want to measure Return Loss over a wavelength
range.
See “Accessories” on page 319 for a list of modules that can be installed in
your mainframe. Refer to the note below that explains the use of highly
coherent light sources.
• 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.
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 length of the signal.
N O T E