Abstract
Since quasi-phase-matching of nonlinear optics was proposed in 1962, nonlinear photonic crystals were rapidly developed by ferroelectric domain inversion induced by electric or light poling. The three-dimensional (3D) periodical rotation of ferroelectric domains may add feasible modulation to the nonlinear coefficients and break the rigid requirements for the incident light and polarization direction in traditional quasi-phase-matching media. However, 3D rotating ferroelectric domains are difficult to fabricate by the direct external poling technique. Here, we show a natural potassium–tantalate–niobate (KTN) perovskite nonlinear photonic crystal with spontaneous Rubik’s cube-like domain structures near the Curie temperature of 40 °C. The KTN crystal contains 3D ferroelectric polarization distributions corresponding to the reconfigured second-order susceptibilities, which can provide rich reciprocal vectors to compensate for the phase mismatch along an arbitrary direction and polarization of incident light. Bragg diffraction and broadband second-harmonic generation are also presented. This natural nonlinear photonic crystal directly meets the 3D quasi-phase-matching condition without external poling and establishes a promising platform for all-optical nonlinear beam shaping and enables new optoelectronic applications for perovskite ferroelectrics.
Highlights
The macroscopic physical properties of condensed matter are associated with constituent functional groups, concentration gradients, as well as their hierarchical spatial arrangement[1,2,3,4,5]
We show an exotic addition to a KTN crystal by selecting a suitable Ta/Nb ratio and produce the first natural threedimensional nonlinear photonic crystal with spatially rotated ferroelectric domains and modulated quadratic susceptibility
The last one has been partially demonstrated in 3D LiNbO3 and Ca0.28Ba0.72Nb2O6 nonlinear photonic crystals[12,13]
Summary
The macroscopic physical properties of condensed matter are associated with constituent functional groups, concentration gradients, as well as their hierarchical spatial arrangement[1,2,3,4,5]. Regardless of the previous 1D, 2D, or 3D quasi-phase-matching examples, the Δk = 0 condition has strict limitations for the crystal cutting direction and incident light polarization for efficient nonlinear energy conversion. In periodic poled LiNbO3 crystals with up–down ferroelectric domains, the incident light direction should be along the x-cut crystal to take advantage of its largest nonlinear susceptibility d33, and the polarization of fundamental and second harmonic light is limited in the z direction[18]. Breaking such constraints has a profound impact on nonlinear photonics. Due to the limitations of traditional poling techniques, a nonlinear optical medium with 3D rotated ferroelectric domains is not feasible and has not been fabricated to our knowledge
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