Azimuth-controlled multicolor shifting based on subwavelength sinusoidal grating.

Subwavelength grating-based color-shifting devices exhibit dynamically tunable spectral responses under specific resonant conditions, offering advanced applications in optical anticounterfeiting and surface decoration. However, conventional devices remain limited by structural complexity, narrow tuning ranges, low energy efficiency, and high manufacturing costs. Thereby, we propose a design methodology for multicolor shifting devices capable of dynamic color shifts through azimuthal angle rotation (i.e., in-plane rotation of the device). The proposed evaluation function can be adjusted to yield the desired spectral response, enabling diverse color shifts from a single template. Optimization of the geometric parameters and azimuth angles of rectangular gratings using rigorous coupled-wave analysis (RCWA) and an immune algorithm, followed by conversion into a sinusoidal structure to simplify large-area fabrication while maintaining performance. Using this approach, quad- and penta-color shifting devices based on subwavelength sinusoidal gratings were designed, achieving peak reflectance exceeding 45 % for all target colors, with maxima reaching 89 %. Additionally, the quad-color shifting device was fabricated using low-cost exposed holographic interferometry, validating the method. The results simplify the structure compared to conventional subwavelength grating filters, while enhancing optical performance and fabrication feasibility, offering a new approach for cost-effective, high-performance dynamic optical devices.