What is Mode Field Diameter?

An overview of Mode Field Diameter and its importance in the development and qualification of single mode fiber.

1. Mode Field Diameter (MFD) Overview

2. •Mode Field Diameter is a measure of
light intensity in a single mode fiber
cross section
•Traditionally, MFD is the width of the
curve where the intensity falls below
1/!"of its peak. While still a good way
to visualize the MFD, the definition has
improved
What is MFD?
•International standards define MFD via
the PetermannII definition which
involves integration of angles obtained
from the far-field intensity distribution
•MFD, as the effective area of the fiber,
is larger than the core with light also
propagating through a portion of the
cladding

3. •Provides information about the cable’s performance and the impact of sources of
loss such as macro and micro bending
•Appropriately matched fibers and sources avoids excessive loss or underfilling
(source-to-fiber and fiber-to-fiber coupling loss)
Why is MFD important?
Deceptively good loss going right to left
Really bad loss going left to right

4. •OP1021 Launch Condition Analyzer
•Farfieldprofile obtained via the direct
farfieldmethod, which is the preferred
reference method for MFD
•Calculations per PetermannII integral
done in OPL-LCA
•MFD included in results and test report
Testing Solution for MFD

5. •TIA/EIA-455-191A and IEC 60793-1-45
•Standards highlight four methods for calculating MFD, with the direct farfieldmethod
being the most direct and thus used to resolve disputes
•MFD is calculated by measuring the farfield
pattern and evaluating the PetermannII
integral using the measured data
•Evaluation of this integral is done in
OPL-LCA following the process
detailed in Annex A of both
standards documents
Standards

6. www.optotest.com
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