Bow-Tie PM Fibers
The bow-tie design was specifically developed to produce birefringence to allow polarization alignment to be controlled throughout the entire fiber system. The fiber core is surrounded on two sides by zones of boron-doped glass with a thermal expansion coefficient well above that of the surrounding quartz glass. This allows two zones with different refractive indices to stand perpendicular to each other.
Together with the core, the cross-section of so-called stress-applying parts (SAPs) looks like a bow tie – hence the name.