Systems and methods for measuring the state of polarization (SOP) for each wavelength channel in a multi-wavelength-channel light beam are disclosed. The system includes a set of two or more rapidly switchable waveplates switched to form a sequence of secondary light beams having different polarizations. A polarizer filters the set of secondary light beams, and a spectral dispersing element spatially divides the secondary light beams into their respective wavelength components. A detector array measures in parallel the intensity of the different wavelength components for each of the polarization-filtered light beams. A controller stores the intensity measurements and calculates the Stokes parameters for each wavelength component, thereby characterizing the SOP for all the wavelength channels of the multi-wavelength light beam.