Minimizing the Effects of Polarization Crosstalk on the Imaging Fidelity of an Optical Interferometer

Many astronomical objects are expected to be strongly polarized on the angular scales accessible with optical and infrared interferometry. Passage of stellar light through the optical trains of a long-baseline interferometer can induce cross talk between the polarized and unpolarized components of the light. As a result, the calibrated interferometric visibilities may depend on a difficult-to-separate mixture of the angular structure and the spatially varying polarization structure of the object being studied, and this will compromise the scientific usefulness of the interferometric data. We investigate the problem of designing a polarization-fidelity interferometer: one that can make accurate maps of the total intensity of an object, even when the object has a significant spatially varying polarized component. We demonstrate that taking polarization issues into account when designing the interferometric train is mandatory even when the interferometer has symmetric arms, and we identify that the key metric for such an interferometer is the diattenuation of the optical train. We evaluate the performance penalties incurred in an interferometer where polarization issues have not been adequately addressed.