For standard single-mode fibers the light is guided in two principle states of polarization. Polarization-maintaining single-mode fibers. In fiber optics, polarization-maintaining optical fiber (PMF or PM fiber) is a single-mode optical fiber in which linearly polarized light, if properly launched into the fiber, maintains a linear polarization during propagation, exiting the fiber in a specific linear polarization state; there is. In polarization-maintaining single-mode fibers (PM fibers), the fiber symmetry is broken by integrating stress elements into the fiber cladding. Polarization-maintaining single- mode fibers (PM fibers) are rotation-ally non-symmetric. The mentioned problem can be fixed by using a polarization-maintaining fiber, which is not a fiber without birefringence, but on the contrary a specialty fiber with a strong built-in birefringence (high-birefringence fiber or HIBI fiber, PM fiber). Provided that the polarization of light launched. Higher-order modes like LP 11, LP 20 etc. then do not exist — only cladding modes, which are not localized around the fiber core.
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