DOP ↔ PER Converter
Degree of polarization ↔ polarization extinction ratio
Enter both measured powers in the same unit (mW, µW, …). Order doesn't matter — the larger one is taken as the wanted axis. PER and DOP above update automatically.
About DOP & PER
DOP: measures how much of the light is polarized (0–100%).
PER: how well a polarization-maintaining component keeps light in the desired polarization state — the ratio of power in the wanted state to the power in the orthogonal, unwanted state.
From two powers: measure the power on each polarization axis and enter both. PER = 10·log₁₀(P_max / P_min); DOP = (P_max − P_min) / (P_max + P_min).
Two numbers for one property
The degree of polarization (DOP) gives the polarized share of the light, in percent. The polarization extinction ratio (PER) compares the power in the wanted polarization with the power at right angles to it, usually in dB. Measure the power on the two polarization axes, Pmax and Pmin, and both follow from those two numbers, so either one gives the other.
DOP = (Pmax − Pmin) / (Pmax + Pmin)
PER = 10 · log₁₀((1 + DOP) / (1 − DOP))
Examples
20 dB PER is a power ratio of 100 : 1, which is a DOP of 99/101 = 98.02 %. 4 mW on one axis and 0.07 mW on the other give a PER of 17.57 dB and a DOP of 96.56 %. Close to 100 % the calculator shows more decimals: 50 dB is a DOP of 99.998 %.