User`s guide

Getting Started with Return Loss How to Choose a Light Source
18 Agilent 81610A/11A/12A/13A/14A Return Loss Module, Fifth Edition
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
If a return loss module with at least one internal source (such as the
Agilent 81611A, 81612A, 81613A or 81614A) 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.
Refer to the “Accessories” section of your mainframe’s User’s Guide
for a list of the modules that can be installed. Refer to the note
below that explains use with highly coherent light sources.
• Tunable Lasers when you want to measure Return Loss over a
wavelength range.
Refer to the “Accessories” section of your mainframe’s User’s Guide
for a list of the modules that can be installed. Refer to the note
below that explains use with 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.
NOTE If you use high-coherence light sources, you can improve performance
by:
• modulating the output signal at 2 kHz or higher, or
• using the coherence control to reduce the coherence length of the
signal.