Zhang Ke, Tang Yiwen, Meng Jinsong, Wang Ge, Zhou Han, Fan Tongxiang, Zhang Di
Opt Express. 2014 Nov 3;22(22):27437-50. doi: 10.1364/OE.22.027437.
Polarization-sensitive color originates from polarization-dependent reflection or transmission, exhibiting abundant light information, including intensity, spectral distribution, and polarization. A wide range of butterflies are physiologically sensitive to polarized light, but the origins of polarized signal have not been fully understood. Here we systematically investigate the colorful scales of six species of butterfly to reveal the physical origins of polarization-sensitive color. Microscopic optical images under crossed polarizers exhibit their polarization-sensitive characteristic, and micro-structural characterizations clarify their structural commonality. In the case of the structural scales that have deep ridges, the polarization-sensitive color related with scale azimuth is remarkable. Periodic ridges lead to the anisotropic effective refractive indices in the parallel and perpendicular grating orientations, which achieves form-birefringence, resulting in the phase difference of two different component polarized lights. Simulated results show that ridge structures with reflecting elements reflect and rotate the incident p-polarized light into s-polarized light. The dimensional parameters and shapes of grating greatly affect the polarization conversion process, and the triangular deep grating extends the outstanding polarization conversion effect from the sub-wavelength period to the period comparable to visible light wavelength. The parameters of ridge structures in butterfly scales have been optimized to fulfill the polarization-dependent reflection for secret communication. The structural and physical origin of polarization conversion provides a more comprehensive perspective on the creation of polarization-sensitive color in butterfly wing scales. These findings show great potential in anti-counterfeiting technology and advanced optical material design.
偏振敏感颜色源于偏振依赖的反射或透射，呈现出丰富的光信息，包括强度、光谱分布和偏振。多种蝴蝶对偏振光具有生理敏感性，但偏振信号的起源尚未完全明确。在此，我们系统地研究了六种蝴蝶的彩色鳞片，以揭示偏振敏感颜色的物理起源。正交偏振器下的微观光学图像展示了它们的偏振敏感特性，微观结构表征阐明了它们的结构共性。对于具有深脊的结构鳞片，与鳞片方位相关的偏振敏感颜色十分显著。周期性的脊在平行和垂直光栅方向上导致各向异性的有效折射率，从而实现形式双折射，导致两种不同分量偏振光产生相位差。模拟结果表明，带有反射元件的脊结构将入射的p偏振光反射并旋转为s偏振光。光栅的尺寸参数和形状极大地影响偏振转换过程，三角形深光栅将出色的偏振转换效果从亚波长周期扩展到与可见光波长相当的周期。蝴蝶鳞片中脊结构的参数已得到优化，以实现用于秘密通信的偏振依赖反射。偏振转换的结构和物理起源为蝴蝶翅膀鳞片中偏振敏感颜色的产生提供了更全面的视角。这些发现显示出在防伪技术和先进光学材料设计方面的巨大潜力。
