嵌入式三色光变器

为了提升现有导模共振防伪光变器件的性能,设计了一种基于ZnS覆盖膜的一维单周期矩形结构三色光变器.当自然光入射角为45°时,可在0°,58°,90°方位角分别获得相应的蓝、绿、红三色反射峰,对研究结果进行了物理解释.分析并提出了该器件周期、槽深、膜厚以及入射角变化对反射峰的影响规律,对器件的设计、制作和测试有重要指导作用.三色光变器基于简单结构实现方位角调节的自然光三色光变效果,可运用传统激光全息产业的模压和蒸镀工艺进行制作,在光变图像防伪领域有重要应用.

Design of embedded tri-color shift device

To improve the performance of existing guided-mode resonance (GMR) anti-counterfeiting grating, a tri-color shift device based on a one-dimensional (1D) singly periodic rectangular structure and ZnS film is reported. By turning the azimuths, the proposed device exhibits tri-color shifts of blue, green, and red for both TE and TM polarizations simultaneously. As the natural light can be considered as a superposition of TE and TM polarizations, in order to achieve the azimuth-tuned tri-color shifts of blue, green, and red, the wavebands and magnitudes of the reflection peaks for TE and TM polarizations should be designed at three azimuths, that is, at the first azimuth, high reflectivity in blue band and low reflectivity in green and red band should be reached; at the second azimuth, high reflectivity in green band and low reflectivity in blue and red band should be reached; at the third azimuth, high reflectivity in red band and low reflectivity in blue and green band should be reached. Considering these design goals, the evaluation function is established. By making the rigorous coupled wave analysis, the 0th reflectivity of the device can be numerically solved, which is relative to the incident light parameters (λ, ψ, φ, θ), the structure parameters (f, T, d_g, d_c), as well as the refractive indices of all the regions (n_i, n_c, n_s). There is no analytical relationship between these parameters and the 0th reflectivity. So genetic algorithm is used to optimize the evaluation function, and then the optimal parameters of the tri-color shift device are obtained. When T=431.5 nm, d_g=124.2 nm, d_c=13.1 nm, f=0.5, and θ =45°, at azimuth angle 0°, natural light has reflection peaks at 468 nm and 442 nm; at azimuth angle 58°, natural light has reflection peaks at 557 nm and 521 nm; at azimuth angle 90°, natural light has reflection peaks at 690 nm, 673 nm, 650 nm and 644 nm. As a result, the device exhibits blue, green and red color responses at 0°, 58° and 90° azimuth, respectively. The research results are explained in physics. Furthermore, the influences of key parameters on the reflection peaks are investigated. It is found that the reflection peaks of blue, green and red light are red-shifted with the increase of device period, groove depth, coating thickness and the decrease of incident angle. When the period, depth, thickness, and the incident angle are changed by ± 4.6% (± 20 nm), ± 27.4% (± 34 nm), ± 100% (± 13.1 nm), and ± 11.1% (± 5°) with respect to the original designs, respectively, the device can well keep the color-shift effects of blue, green and red. The results above are meaningful in the designing, manufacturing and testing of the device. Compared with the existing GMR anti-counterfeiting grating, the tri-color shift device has high anti-counterfeit and appreciative value because of the harder designing and richer visual effect. Moreover, the 1D simple periodical structure is good for the manufacture of the high-precision master masks, and the device can be massively produced at low cost by the traditional embossing and evaporating technique in the laser holography industry. This tri-color shift device breaks through the limit of bi-color shifting technology, and may have great applications in the field of the optically variable image security.