Efficient Noncollinear Second‐Harmonic Generation in Pb(In _1/2 Nb _1/2 )O ₃ ‐Pb(Mg _1/3 Nb _2/3 )O ₃ ‐PbTiO ₃ Crystals Through Domain‐Engineering

Abstract Achieving broadband and effective frequency conversion through non‐collinear phase matching (PM) is of significant interest due to its potential applications in all‐optical signal processing. To overcome the stringent requirements of the quasi‐phase‐matching condition, such as the period width, polarization, and incident direction, perovskite‐type ferroelectric materials with natural ferroelectric domains offer advantages for achieving broadband second‐harmonic generation (SHG). However, the random distribution of lattice vectors and scattering at domain walls not only causes substantial scattering losses, limiting conversion efficiency, but also complicates detection and application. In this study, we present a new type of nonlinear photonic crystal by constructing a domain structure with a regular distribution of polarization vectors in a Pb(In _1/2 Nb _1/2 )O ₃ ‐Pb(Mg _1/3 Nb _2/3 )O ₃ ‐PbTiO ₃ (PIN‐PMN‐PT) crystal. This structure enables SHG with increased efficiency (6 × 10 ⁻⁵ ) at fundamental wavelengths ranging from 1064 to 1340 nm without the need for angle or temperature tuning. Additionally, this unique domain structure facilitates the spontaneous deviation of the SHG emission direction from the propagation direction of fundamental‐frequency light (FL), thus eliminating detection and application challenges. This work presents a new method of achieving broadband and efficient noncollinear SHG using domain engineering, and also pushes the boundaries of frequency conversion techniques in ferroelectrics.