Abnormal optical anisotropy in correlated disorder KTa_1-xNb_xO₃:Cu with refractive index gradient

In this report, an abnormal optical anisotropy in KTa_1-xNb_xO₃:Cu (Cu:KTN) crystals with refractive index gradient is presented. Contrary to general regulation in a cross-polarization setup, the transmitted intensity of both TE (horizontally polarized) and TM (vertically polarized) lasers aligned with the basic crystallographic directions can be modulated quasiperiodically. The mechanism is supposed to be based on the polarization induced by the temperature gradient and the refractive index gradient. Meanwhile, the correlated disorder property of the crystals in the range of the freezing temperature (T_f) and the intermediate temperature (T ^*) also plays an important role. With the results verified both theoretically and experimentally, we believe this work is not only beneficial for the development of the theory associated with the correlated disorder structures in relaxor ferroelectrics, but also significant for the exploitation of numerous optical functional devices.