PSY-201 User Guide
GP-UM-PSY-201-11
Page 8 of 105
Figure 2
a) Free space construction of variable retardation plate polarization controller
b) Fiber squeezer construction of variable retardation plate polarization controller
Any polarization state of monochromatic light can be represented as a point on the
Poincaré Sphere, as shown in Figure 3. In principle, increasing the voltage (increasing the
squeezing pressure) on one fiber squeezer (X1 or X3) effectively causes the polarization state to
rotate clockwise about the OQ axis while decreasing the voltage causes the point to rotate
counter-clockwise. Likewise, increasing the voltage to a fiber squeezer (X2 or X4) oriented 45°
from the first one should cause the polarization state to rotate clockwise about an axis (OH axis)
orthogonal to the first one, while decreasing the voltage should rotate the polarization
counterclockwise. In practice, because of the presence of other birefringences, two parallel fiber
squeezers do not always rotate the polarization about the same axis. However, it has been proven
to be possible to generate any polarization state from an arbitrary input polarization state using
this system.
Strictly speaking, a 3-axis fiber squeezer polarization controller is sufficient to generate
any state on the Poincaré sphere. However, adding more fiber squeezers to the system provides
more degrees of freedom, enabling reset-free operation, a highly desired feature for many
dynamic applications. The PSY-201 uses a 6-axis version of the fiber squeezer based PolaRite™ III
polarization controller to achieve rapid, reset-free polarization control.
