Polarization extinction ratio is the ratio of optical powers of perpendicular polarizations, usually called TE (transverse electric) and TM (transverse magnetic). It is a key characteristic of optical systems where coherence is of interest - only signals with the same polarization can be used for interference. PER can be expressed in decibels, dB, and calculated using the formula below.
PER is also an important parameter of fiber optic delay lines in case of polarization-sensitive applications such as coherent beam combining. Maintaining a high PER requires using dedicated polarization-maintaining (PM) fibers, ensuring careful alignment of connectors, and minimizing stress-inducing bends or twists in the fiber.
