Left: typical lab fringes obtained on one baseline when scanning the optical path difference (OPD). The four fringe patterns are in quadrature. Right: polar diagram of the 120 contrasts (along the radius) and 120 phase shifts (along the perimeter) measured in the lab over the K band for the IO assemblies. Each colour corresponds to an assembly. The dotted lines display the mean phase shiftvalues. For comparison with the requirements, we displayed the phase differences designed to be 90° or 180°.