Reversible phase transition for switchable second harmonic generation in 2D perovskite microwires

Abstract Highly efficient second‐harmonic generation (SHG) has facilitated the development of nanophotonics and sustained promising applications, ranging from electro‐optical modulation, frequency conversion, and optical frequency combs to pulse characterization. Although controllable SHG switching has been observed in nanophotonics structures and molecule systems, the relatively small SHG switching contrast impedes its application in switchable nonlinear optics. Herein, reversible phase transitions between glassy and crystalline states without material degradation are demonstrated based on solution‐processed chiral perovskite microwire arrays. Breaking of lattice inversion symmetry and high crystallinity support efficient SHG in microwire arrays. By synergy of high‐performance SHG and reversible phase transitions between glassy and crystalline states, reversible switching of SHG is demonstrated under facile conditions. The high SHG switching performances, together with a small footprint, pave the way toward the integration of switchable nonlinear devices based on microwire arrays.