Suppose you have source of coherent light, a laser beam, with +45 polarization. A polarizing beam splitter (PBS) splits the beam into its horizontal and vertical components. The second polarizing beam splitter recombines them into a single beam again. If the two paths between the two PBS are of equal length and there is nothing else in them that would cause a phase shift, I'd assume the output polarization is equal to the input polarization: +45.
What is the output polarization if you place an attenuator in the path of the horizontal component? How do you calculate it?