According to an example, a polarization control system is to manipulate polarization manipulators to output light that achieves a trajectory on a Poincaré sphere that tracks a known trajectory of a polarizer on the Poincaré sphere, in which the trajectory of the output light enables definition of a reference polarization state of the output light. The polarization control system may also manipulate an output polarization manipulator to set the output light to a predefined polarization state based upon the reference polarization state.