Broadband nonlinear Bragg diffraction from self-assembled structures in potassium tantalate niobate crystals

Nonlinear optical process is a key technology to realize optical communication. Potassium tantalate niobate (KTa_1−xNb_xO₃, KTN) crystals with large nonlinear optical coefficients are potential functional materials for realizing χ² nonlinear optical processes. However, to accurately modulate the nonlinear optical signals of KTN crystals, the relationship between their second harmonic generation (SHG) properties and ferroelectric domain structures needs to be further investigated. Here, we report the special SHG processes generated by self-assembled structures in KTN crystals. Multimode quasi-phase matching and broadband nonlinear Bragg diffraction are achieved with the changing of polarizations and wavelengths of the fundamental wave. The physical processes behind the multi-polarization and multi-wavelength SHG properties of the KTN crystals are revealed. Our results about the multi-polarization and multi-wavelength SHG properties of KTN crystals will provide guidance for the design and realization of multimode nonlinear optical processes.