Q factor measures the quality of an analog transmission signal in terms of
its signal-to-noise ratio (SNR).As such, it takes into account physical impairments to the signal –
for example, noise, chromatic dispersion and any polarization or non-linear effects – which can
degrade the signal and ultimately cause bit errors. In other words, the higher the value of Q factor
the better the SNR and therefore the lower the probability of bit errors.