The invention includes methods and apparatuses to adjust an optical signal transmitted through an optical amplifier, such as in a wavelength division multiplexed optical network. The methods and apparatus of the invention calculate polarization effects which cause degradation to the optical signal. A measurement of the polarization-related degradation of an optical signal is calculated by using at least one reference signal. In some embodiments of the invention, the reference signal is depolarized or has scrambled polarizations. The invention is typically used in long-haul optical networks.