Unitary transformation of the polarization state of biphoton field, using the quasiperiodic domain structure of KH/sub 2/PO/sub 4/

Summary form only given. Potassium dihydrogen phosphate (KDP) is one of the best known ferroelectric crystals. It undergoes the ferroelectric phase transition at 123 K and forms a quasiperiodic domain structure, where the domains have the shape of plane layers. A schematic drawing of domain system is shown. We propose an efficient method, where KDP plays not only the role of biphoton´s birthplace, but also as an stable interferometer of high efficiency. Besides, applying the constant electric field on the surface crystal planes we can change the thickness of domains and thus change the output polarization.