间隔叠合式双层亚波长光栅

提出了一种应用价值较高的防伪光栅结构-间隔叠合式双层亚波长光栅,可以展宽基本光栅的光谱峰值带宽、改善光谱线形和光变效果.分析了亚波长光栅光谱峰值带宽展宽和线形改善的原理,用矢量衍射理论验证了理论分析的合理性,并对特定防伪光变设计要求的双层光栅进行了参量优化和光变特性分析.结果表明,满足同相位条件的光谱线形与基本光栅相同,带宽为基本光栅的两倍;满足反相位条件的光谱线形为准矩形,带宽大于基本光栅;亚波长光栅在传统和非传统照明条件下倾斜均能产生彩色光变效果,且传统照明情况下的光变速率较大,利用这种光变速率差可以制作各向异性光变效果.

Non-Contact Cascaded Dual-Layer Sub-Wavelength Gratings

A non-contact cascaded dual-layer sub-wavelength grating is presented. It can broaden the spectral peak linewidth, modify the spectral lineshape and improve the optical variable effect of basic sub-wavelength gratings. It is a kind of security grating configuration with potential for achieving application in industry. The mechanisms for the broadened linewidth and improved lineshape are analyzed and validated with the vector diffraction theory. The structural parameters of dual-layer gratings with special requirements of change in color are optimized and their optical variable characteristics are also studied. The results show the spectral lineshape of dual-layer gratings cascaded in phase is similar to that of basic gratings with a linewidth twice that of basic gratings; the out-of-phase arrangement yields lineshape exhibiting broadened peaks and narrower bases with a wider linewidth. Dual-layer gratings always show optical variable effect when tilted at traditional or nontraditional incident illumination and the optical variable velocity of the former is the quicker than that of the latter which can be used to design and fabricate anisotropic optical variable image devices.