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Then the polarization-maintaining fibers was invented to overcome this problem. The polarization-maintaining fibers are designed in such a way that two perpendicular polarized modes are forced to travel at different propagation constants, which means they travel at different velocity. This difference in velocities makes it very hard for optical energy to transfer between each other. As the result that polarization state of input laser beam is preserved. This special purpose fiber is commonly used in fiber optic sensing, interferometry and slab dielectric waveguides.
Cross Section of Polarization Maintaining Fibers
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Figure. 4. Cross Section of Polarization Maintaining Fibers: [http://www.fiberoptics4sale.com/wordpress/what-are-polarization-maintaining-fibers/|http://www.fiberoptics4sale.com/wordpress/what-are-polarization-maintaining-fibers/] \[4\] |
The above three pictures illustrated the three different types of polarization maintaining fibers, which are Panda, Elliptical-clad, Bow-tie. There fibers contain a unique feature; they have stress rods in fibers (a feature not seen in other fiber types). The stress rods are two circles in the Panda PM fiber, a elliptical clad in elliptical-clad PM fiber and two bow-ties in the Bow-Tie type PM fiber. The most important property of stress rods is that it creates stress in the core of the fiber such that the transmission of only one polarization plane of light is favored.
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Video.1. A Brief Introduction of the Polarization-maintaining Fibers: [http://www.youtube.com/watch?v=7rrb-_Iin-g|http://www.youtube.com/watch?v=7rrb-_Iin-g] \[5\] |
References:
Principle of operation - Special purpose fiber - http://en.wikipedia.org/wiki/Optical_fiber
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