Multistate polarization addressing using one single beam in an azo   polymer film
  Peculiar light-matter interactions can break the rule that a single beam polarization can address only two states in an optical memory device. Multistate storage of a single beam polarization is achieved using self-induced surface diffraction gratings in a photo-active polymer material. The grating orientation follows the incident light beam polarization direction. The permanent self-induced surface relief grating can be readout in real time using the same laser beam. 
S. Ahmadi Kandjani, R. Barille, S. Dabos-Seignon, J.-M. Nunzi, E.   Ortyl, S. Kucharski