apparatus for making wavelength - resolved polarimetric measurements comprises an interferometric source , for example a broadband source and an optical interferometer unit , and a polarization generator unit for generating different states of polarization of light received from the interferometric source and applying same to a device - under - test . a polarimeter unit receives and polarimetrically - analyzes light from the device - under - test , converts the polarimetrically - analyzed light into electrical signals , and , using fast fourier transform numerical analysis , computes therefrom the wavelength - resolved polarimetric measurements . placing the optical interferometer unit “ upstream ” not only of the device - under - test , but also of the polarisation generator unit , means that the latter substantially eliminates polarization dependent effects introduced by the former . the polarimeter can still perform the necessary transformation even though the interferogram has been passed through the polarisation generator unit and the device - under - test .