The compensation mechanism may be a glass plate that is disposed in {HEAD ~ an optical path} of {TAIL ~ a polarization component} so that the optical path length of that polarization component can be made substantially equal to the optical path length of the other polarization component that traverses through a half wave plate 
The compensation mechanism may be a glass plate that is disposed in { HEAD ~ an optical path } of { TAIL ~ a polarization component } so that the optical path length of that polarization component can be made substantially equal to the optical path length of the other polarization component that traverses through a half wave plate
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH