Binary Birefringence In Ferroelectric Super-Crystals

The state of polarization of light is strongly affected by anisotropy and exotic polarization phenomena can be observed in systems where this anisotropy emerges on symmetric and ordered structures on the wavelength scale, as occurs in metamaterials [1, 2] and periodically-poled multiferroic media [3]. In recent studies, conditions have been found in which the dipolar mosaic characterizing disordered ferroelectric materials spontaneously settles into a three-dimensional coherent and periodic structure, a ferroelectric super-crystal with remarkable optical properties [4] (Fig. 1(a)). Here, we investigate the dynamics of polarization in a photonic super-crystal supported by the ferroelectric phase of a disordered potassium sodium tantalate niobate sample. We report an anomalous birefringent effect for which light suffers various degrees of depolarization remaining fully polarized only for two specific input states that correspond to the orthogonal linear polarizations along the lattice principal axes, whereas full depolarization occurs for the conjugate input states in the Poincareu0027 sphere. Specifically, Stokes parameters measurements shown in Fig. 1(b) demonstrate how the degree of polarization strongly depends on the direction θ in of linear input state, with the polarized fraction of light that is mainly characterized by the in-plane/out-of-plane component SH. The depolarized state is a spatial distribution of polarized fields with different dephasing. On the Poincareu0027 sphere input states on the surface evolve to output states that are distributed in proximity to the SH diameter (Fig. 1(c)). Therefore, in Poincareu0027 space, the system behaves like a projector and the transfer matrix has the form M = (1, 0; 0, 0). This unconventional behavior, that we call binary birefringence, does not depend on the crystal orientation and on the wavelength. We are able to attribute the phenomenon to the birefringent response of the waveguiding array supported by the specifically-ordered periodic ferroelectric state. Consistently, the standard Malus-like behavior is recovered when domain ordering weakens and reduces to a disordered network of polar-nanoregions, ultimately disappearing in the paraelectric phase. Our results show how spontaneous ferroelectric photonic crystals manifest a polarization transfer matrix that depends on the microscopic dipolar arrangement and support hereto unexplored functional operations on transmitted light.