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PAX1000
8.4.3 Correction of the Polarimeter ER Measurements
When performing ER measurements on PM fibers with a polarimeter, the DOP will not affect
the measurement results and only the relative polarization changes (circle on the Poincaré
Sphere) are taken into account.
Correction for absolute ellipticity
Ideally, optimally coupling linearly polarized light into either the slow or fast axis of the PM fiber
ensures that linearly polarized light will be output from the fiber. However, externally applied
mechanical stress, such as from fiber connectors, can cause the propagating light to undesir-
ably couple into the orthogonal polarization. This cross-coupling will transform the linearly polar-
ized light into elliptically polarized light. A polarimeter measurement can determine the ER of
the output light, as shown in the figure below.
ER Measurement Screen of a Thorlabs PAX1000
The center of the circle represents the center Azimuth and Ellipticity. It should be positioned on
the equator. As the light is predominantly linearly polarized, the center of the circle should be
positioned on the equator. Each measurement point can be expressed as an Azimuth / Ellipti-
city pair. Plotting all measurement points will describe a circle. The measurement value which is
most distant from the equator has the maximum ellipticity.
In above example, the measurement of the ER was 21.51dB. This measurement is based only
on the relative polarization changes (circle on the Poincaré Sphere) during the measurement.
The radius is 9.61°. The formula to calculate the ER is as follows:
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