Femtosecond Laser-Induced Refractive Index Modulation of 2D Perovskites for Phase-Modulated Holographic Neural Networks

Laser direct writing functional optical materials enable high-resolution and optically thin computer-generated holograms with a wide range of applications. However, the traditional material system limits the development of holography technology due to the small refractive index modulation, high optical loss, and complicated preparation process. Perovskite has emerged as competitive candidates because of their superiority in high refractive index, flexible bandgap tunability, and low-cost preparation. Here, we report giant refractive index modulation of perovskites by femtosecond laser direct writing (FsLDW) for applications in holograms and holographic neural networks (HNNs). The interaction mechanism between the femtosecond laser and perovskites is also investigated. Under the precise control of FsLDW, the organic phenylethylamine (PEA) functional groups are reduced, leading to giant refractive index modulation from 0.15 to 1.05 at the broad wavelength range of 519–900 nm, along with geometric thickness reduction. Phase-modulated perovskite holograms and HNNs composed of cascaded holographic plates are demonstrated, greatly expanding the possibilities of perovskite applications in the field of all-optical information encoding.