polarisationdivision

Polarisation division refers to techniques that treat the two orthogonal polarization states of light as separate channels or components for analysis or communication. In optics and photonics, polarization refers to the orientation of the electric field; orthogonal polarization states are linearly polarized at 90 degrees or circular/elliptical states that are mutually exclusive. Polarisation division of signals, often called polarization-division multiplexing in communications, seeks to transmit distinct data streams using the available polarization modes, effectively increasing channel capacity in ideal conditions.

Mathematically, the behaviour of polarization states can be described using Jones calculus for fully polarized light, where a signal is represented by a two-component complex vector and the transfer of the medium by a 2x2 Jones matrix; for partially polarized light, Stokes parameters and Mueller calculus are used. In practical systems, devices such as polarization beam splitters, polarization controllers, and waveplates are used to separate, combine, or rotate polarization states. Coherent detection with digital signal processing allows compensation for polarization mode dispersion and cross-polarization interference.

Applications include fiber-optic communications, where polarization-division multiplexing improves spectral efficiency; free-space optical links where polarization can be maintained or controlled; and certain imaging or sensing techniques that extract information from polarization states. Advantages include higher data rates and improved use of the optical channel; challenges include sensitivity to polarization changes caused by propagation media, requiring polarization tracking and compensation, and potential cross-talk between channels due to non-ideal separation.

Polarisation division has historical roots in the development of polarization multiplexing in the 1990s and 2000s, with ongoing advances in modulation formats and digital signal processing enabling higher-order polarization-division systems.