Polarizationmode

Polarization mode refers to a distinct propagation channel of an electromagnetic field in which the light has a defined polarization state. In general, a mode is a solution to Maxwell’s equations that satisfies the boundary conditions and geometry of a medium or structure, and a polarization mode is an eigenmode whose transverse electric and magnetic field components describe a specific polarization. In isotropic media, different polarization states are degenerate, while in birefringent or anisotropic media, two or more polarization modes propagate with different phase velocities and effective refractive indices.

In optical fibers and waveguides, polarization modes often appear as two principal states that can be linear, circular, or elliptical. Polarization-maintaining fibers are designed to support and preserve a chosen polarization axis, reducing cross-coupling between modes. External perturbations such as bending, temperature changes, or mechanical stress can couple energy between polarization modes, giving rise to polarization mode dispersion (PMD). PMD is the difference in arrival times of the polarization components and can limit the performance of high-speed communication systems. It is characterized by PMD coefficients and is mitigated through fiber design, dispersion management, and, when needed, active compensation.

In laser resonators and integrated photonic devices, polarization modes correspond to TE/TM or other polarization eigenmodes of the cavity or waveguide. Mode competition and polarization control elements, such as polarizers and waveplates, influence the excitation and stability of particular polarization modes. Understanding polarization modes is essential across applications in telecommunications, sensing, imaging, and laser technology.