Exploring the structural color of micro-nano composite gratings with FDTD simulation and experimental validation

The significance of micro-nano composite gratings (MNCGs) resides in their applications, including optical devices, sensors, and diffractive elements, which drive research interest in their diffraction characteristics. This study investigates both the diffraction characteristics of MNCGs and the factors that influence them by employing both Finite-Difference Time-Domain (FDTD) methods and experimental validation. The initial focus lies in deciphering the differences in diffraction characteristics between micro-gratings (MGs) and MNCGs by analyzing the coupling effects, diffraction order, color distribution, and intensity variation. Additionally, this research emphatically investigates five aspects to discover the influencing factors of MNCG's diffraction characteristics, such as the height, groove angle of MGs and the period, blaze angle, and height of nano-gratings (NGs). Results show that the structural coloration and saturation of MNCG surpass that of MG. NG plays the actual spectral role, and a reduction in the period of NG leads to enhanced splitting light capability of the white light. The optical detection tests validated the simulation results. The present study reveals the diffractive properties of MNCGs, providing technical insights for the design and processing of optically variable devices.