Following the solved issue of PSD saturation, I computed again calibration parameters (see figures 1 to 3).

Then, I computed polarization map with input polarization s (figure 4) and 15 deg (figure 5).

From these measurements, I could compute delta n and theta (figure 6) as well as polarization conversion losses (figure 7).

The 2 methods to estimate these losses agree well with each other and show losses at about 0.74 % !

We will fine tune the mirror rotation angle (seems we still have an offset about 2.37 deg or 4.65 arc length cord).