Hi all, I'm a bit confused about the polarization state of the photons after the BBO. I am aware that they are polarized orthogonally, but are they polarized according to a certain axis? The reason I'm asking is that one article I read seems to imply that that's not the case: i.e. the polarizations are orthogonal, but they may still be at any angle. However, Wikipedia states that the QWP produces circularly polarized photons. But if I'm not mistaken, a QWP only produces circularly polarized photons if the angle of the QWP is exactly 45 degrees relative to the photon's polarization. Otherwise it will produce elliptically polarized photons, or even linear if the incoming angle is exactly that of the QWP. So which of the two is true? By the looks of it they are always parallel to either the x or the y axis, but it can be either for either particle. Is that true? Thanks in advance!