Optical Q-factor

The Q-factor (quality factor) is a statistical measure of received optical-signal quality, determined from the distribution of the logical "0" and "1" levels and their noise, directly related to the expected BER level.

How is the Q-factor determined?

The Q-factor is calculated from the difference between the average signal levels for "1" and "0" bits, divided by the sum of their standard deviations (noise). The higher the Q value, the lower the expected BER — this relationship is described by a standard analytical formula, widely used in system simulations instead of very long Monte Carlo simulations for low BER values.

Applications

The Q-factor is used in designing and optimizing DWDM links as a fast transmission-quality indicator, letting you compare design variants (transmit power, modulation type, amplifier configuration) without needing to simulate billions of bits.

Related terms

BER

EDFA

DWDM