How to distinguish the fast and slow axes of polarization-maintaining fiber
The fast axis is the direction of the small refractive index, the faster optical axis of light transmission, perpendicular to the midpoint of the line connecting the centers of the two stress zones; the slow axis is the optical axis that passes through the end of the two stress. In polarization-maintaining single-mode fibers (PM fibers), the fiber symmetry is broken by integrating stress elements in the fiber cladding. The light is then guided in two perpendicular principle states of polarization with different propagation constants – the fast and the slow axis.
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