Polarisationsmultiplexing

Polarisationsmultiplexing, often referred to as polarization-division multiplexing (PDM), is a method used in optical communications to transmit multiple data streams on a single optical carrier by exploiting two orthogonal polarization states of light. By sending independent signals on two polarization channels, the aggregate data rate can be effectively doubled without increasing the optical bandwidth.

In fiber-optic systems, PDM is implemented by modulating data on two polarization axes that are kept orthogonal, commonly described as the two principal states of polarization. At the receiver, coherent detection and digital signal processing separate the streams, typically using a 2x2 MIMO equalizer to compensate polarization mixing and crosstalk. The approach requires control of the input polarization, robust polarization tracking, and compensation for polarization mode dispersion (PMD).

PMD, polarization-dependent loss, and random polarization rotation along the fiber can lead to signal degradation if not managed. Other challenges include polarization leakage, coupling losses, and sensitivity to environmental changes. Modern systems address these issues with adaptive polarization control, fiber designs that minimize PMD, and DSP-based demultiplexing.

Polarisationsmultiplexing is widely used in contemporary long-haul and metro optical networks, especially with coherent detection in dense wavelength-division multiplexing (DWDM). It enables higher spectral efficiency and complements other multiplexing schemes, such as space-division multiplexing in research contexts, and is compatible with high-order modulation formats like QPSK and 16QAM.