Á mentioned carlier, bending in the optical fiber leads to a linear birefringence, i.e., the two eigen SÓP of the system are linearly polarized. The fast SOP oriented in the plane of the bend ( say y-axis) and the slow one perpendicular to it ( say x-axis). The amount of this birefringence can be controlled by varying the bend radius and the number of bends or loops in the fiber. It can easily be shown using Eq... that for a typical silica fiber, the phase difference accumulated between the two eigen-SOPs in N fiber loops each of radius R is given by.These wave plate can either be used independently or in a suitable combination to transform the sop of incident light from one state to another as in a lolarization controller discussed below.An all-fiber polarization controllerA proper sequence of three wave plates- QWP followed by a HWP and then followed by another QWP with proper orientations can convert the SOP of the input light to any desired output SOP. The resulting device is known as a polarization controller (52) The device works in three steps: convert the given elipic SOP to a linear SOP, rotate the linear SOP to anothe appropriate liear Sop, and finally impart to it the required elipticty to obtain the final desired SOPThe advantage of this device is thats it is in an “all-fiber” form. In many interferometric and polarimetric fiber sensors, one requires acontrol over the sop of light propagating in the fiber. In those cases, this polarization controller finds immense use, as it has to be just spliced at two ends in between a fiber linhk. One does not need to depend on bulk-optic components for these purposes, which are lossy as well as difficult to integrate with optical fibers.
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