摘要
近年来,超材料和超表面因为一些不同于传统材料的新奇性质一直被广泛研究,而基于超材料或者是超表面的波前控制也是其中的一个热门研究领域.迄今为止,已经提出了很多不同的结构来对反射光和透射光的波前进行调控,在已知的结构中,反射光的波前调控效率已经可以达到较高数值,但是很少有报道能够使用超材料简单高效地调制透射光的波前.本文提出了一种由相同几何结构的左旋和右旋结构复合而成的螺旋超材料.通过使用时域有限差分方法进行仿真,发现这种螺旋结构将会在入射光和透射光之间引入一个可控的相位变化,从而可直接对透射光波前进行调控.仿真结果还表明,该复合结构螺旋超材料在较宽的波长范围内可以达到近64%的透射率.最后通过将该螺旋材料沿着X轴排布成有着连续相位变化的阵列,可以在近红外区域(1.0—1.4μm)观察到反常折射现象,仿真结果与理论计算得出的反常折射角十分符合.
Metamaterials or metasurfaces have been widely studied to manipulate the propagation of light by controlling the wavefront. In previous work, more and more structures were designed to study the reflected or the transmitted light. However, as far as we know, it is rarely reported how to efficiency tailor the wavefront, especially for transmitted light. Helical metamaterial, which has a relatively strong coupling effect among the helical nanowires, may provide an alternative to the wavefront control. In this study, a kind of complementary helical metamaterial with a left-handedness and a right-handedness helixes coupled to each other is proposed. The complementary helical metamaterial has a strong circular conversion dichroism, and it is expected to be a good candidate for generating phase shift and controlling wavefront with high efficiency. Using the finite-difference time-domain method, we find that this kind of helix has a high circular polarization conversion in a broadband, which often implies a high efficiency of the transmitted light. Moreover,it is also found that the structure will introduce a controllable phase shift（Ф） between the incident and the transmitted light whose polarizations are orthogonal to each other. By calculating the surface current density of the helix, the performance of high circular polarization conversion is explained. Meanwhile, we also find that the phase shift has a linear relationship with the initial angle of the helix（θ）, which is Ф = ±2θ. This relationship can be explained exactly by Jones calculus. According to the generalized Snell＇s law, the refracted beam can have an arbitrary direction by designing a suitable constant gradient of phase discontinuity. And then, by arranging 12 helixes in an array with a constant phase gradient along the X-axis, the phenomenon of anomalous refraction with a high efficiency（64%） is observed in the near infrared range（1.0–1.4 μm）. The angle of the anomalous refraction is in good agreement with the theoretical value.
出处
《物理学报》
SCIE
EI
CAS
CSCD
北大核心
2016年第21期290-297,共8页
Acta Physica Sinica
基金
国家自然科学基金(批准号:61475058)
武汉科学技术资金(批准号:2015010101010001)
深圳基础研究项目基金(批准号:JCYJ20140419131733980)
高性能复杂制造国家重点实验室开放基金(批准号:Kfkt2013-07)资助的课题~~
关键词
超材料
螺旋结构
波前控制
圆偏光转换
metamaterials
helical structure
wavefront controlling
circular polarization light
