1. Polarization Measurements
Lecture-1
Polarization Measurements

2. Polarization Measurements
Retardance Measurements
Retardance is a measure of the differential phase shift of light in the eigenmodes, more commonly referred to as the fast and slow waves.
There are two accurate methods for retardance measurement.
a) The Poincare sphere method
b) Jones matrix measurement method.

3. Polarization Measurements
The Poincare sphere method
This method determines retardance from the pattern traced out on the Poincare sphere when the retarder under test is rotated in a linearly polarized beam.
The polarization reference frame is not strictly necessary for this method, but it can simplify interpretation of the graphical results.

4. Polarization Measurements
Jones matrix measurement method.
The retardance of a two-port device can be determined from the Jones matrix.
The measurement setup is identical to that of the Poincare sphere method.

5. Polarization Measurements
Measurement of Cross-talk in polarization-maintain fiber.
The term polarization-maintain (PM) refers to a class of highly linearly birefringent single mode fiber. PM fiber is typically used to guide linearly polarized light from point to point, for example between a DFB laser diode and a lithium–niobate modulator in a high speed telecommunication system.

6. Polarization Measurements
The crossed-polarizer cross-talk measurements.
The polarimetric cross-talk measurements.
Measurement of cross-talk along a PM fiber.
Cross-talk measurement of PM fiber interfaces.
Measurement of the polarization stability of cascaded PM fibers.

7. Polarization Measurements
The crossed-polarizer cross-talk measurements.
To avoid interferometric effects, a spectrally broad optical source is used.
An unpolarized source gives the advantages that coupling to the input of the test fiber is independent of rotation of the input polarizer.
Measurement results can be affected by source instability and by variation of the optical coupling.

8. Polarization Measurements
The polarimetric cross-talk measurements.
The optical source must be highly polarized, exceeding the cross-talk to be measured by at least 10 dB.
The source spectrum must be narrow enough that the source coherence time is much larger than the difference in propagation time between the fast and slow axes of the fiber under test.

9. Polarization Measurements
Measurement of cross-talk along a PM fiber.
Light is linearly polarized and coupled into the fiber at an initial orientation.
The cross talk is measured by gently heating a short length of fiber immediately following the launch.

10. Polarization Measurements
Cross-talk measurement of PM fiber interfaces.
Degradation of cross-talk due to a PM fiber interconnection is best determined by launching linearly polarized light into a single polarization mode of the first segment and then measuring the cross-talk on either side of the connection by heating the corresponding fiber.

11. Polarization Measurements
Measurement of the polarization stability of cascaded PM fibers.
If polarized light is not perfectly confined to a single axis, slight changes in fiber length caused by heating or movement can cause the output state to wander.
This problem is compounded when several PM fibers are cascaded.