Magnetic Photonic Crystal for Adaptive Flexible Lasers and Secure Encoding

Abstract Responsive photonic crystals (PCs) are attractive because of their unique photonic bandgap (PBG) effect, but existing systems tend to have challenges such as narrow PBG tuning range, slow response to external stimuli, poor reversibility, and difficulty in device integration. To address these issues, magneto‐responsive colloidal PCs have been developed with the advantages of fast response, high sensitivity, good reversibility, and contactless manipulation. In addition, magneto‐optical responsive flexible lasers are developed to bring new solutions for information encryption and anti‐counterfeiting. Combining magnetic nanoparticles and spiropyran molecules to create a composite film that can be both magnetically and optically color‐changing, achieving non‐contact, multi‐stimulus‐responsive color‐changing, and expanding the application fields for color display and anti‐counterfeiting technologies. Further, a flexible laser is designed that achieves efficient and reversible laser wavelength tuning from 580 to 700 nm through dual control of the förster resonance energy transfer effect and magnetic field and UV irradiation. This laser's wavelength tuning combines the structural regulation of magnetic particles with the photo‐responsive properties of spiropyran. It not only advances the field of optical communication but also enhances the security of information encoding and anti‐counterfeiting through the synergy of magneto‐ and photochromism, bringing revolutionary improvements to anti‐counterfeiting technology.