The difference between polarization extinction ratio and degree of polarization

Polarization extinction ratio and polarization degree are both physical quantities that describe the polarization state of light, but their meanings and application scenarios are different.

Polarization Extinction Ratio (PER) refers to the ratio of the transmitted or reflected light intensity of a device in different polarization directions. It is also commonly called the polarization splitting ratio and is commonly found in optical components such as polarizing fibers and polarizing beam splitters. Specifically, when a beam of light passes through these devices, only the light that conforms to a specific polarization direction can be completely transmitted or reflected, while the light perpendicular to this direction will be mostly blocked, which forms the so-called extinction phenomenon. . Therefore, the polarization extinction ratio refers to the ratio between the maximum transmittance and the minimum transmittance of light in the extinction state, usually expressed in decibels (dB).

Polarization Degree (PD) refers to the degree of polarization of a light wave. It can be used to quantify the direction and amplitude of the electric field vector in space, usually expressed as a decimal between 0 and 1. For linearly polarized light, the degree of polarization refers to the proportion of the component of the electric field vector in a certain direction to the total electric field vector. For circularly polarized light, the degree of polarization refers to the proportion of polarization intensity in the rotation direction to the total intensity.

It can be seen that both the polarization extinction ratio and the degree of polarization are physical quantities that reflect the polarization characteristics of light, but the polarization extinction ratio is more used to describe the device's ability to process different polarized light, such as polarization splitting, filtering, etc., while the degree of polarization It is more commonly used to describe the polarization state of a light source or transmission system. In addition, the polarization extinction ratio is usually a finite value that depends on the characteristics of the device itself, while the polarization degree can be measured in any light field and represents the polarization state of the optical element with low accuracy requirements.