双层金属纳米光栅的TE偏振光异常透射特性

根据在亚波长金属光栅表面添加电介质会引起TE偏振光的透射异常性, 应用严格耦合波理论和时域有限差分方法, 研究了双层金属纳米光栅在TE偏振光入射时产生的异常透射现象. 利用等效折射率方法建立了双层金属光栅的等效模型, 得到了TE偏振光透射率与聚合物的折射率、厚度以及金属层厚度的变化关系. 确认了结构中聚合物是透射异常出现的必要条件, TE偏振光以波导电磁模式在其中传播, 并认为类Fabry-Perot腔谐振是透射峰值产生的主要原因.

Extraordinary optical transmission through bilayer metallic nano-grating for s-polarization light

Based on the phenomenon of the s-polarization extraordinary optical transmission through subwavelength metallic grating on a dielectric film, the same phenomenon in bilayer metallic nano-grating has been found. In order to analyze the s-polarization transmission in this specific structure, the rigorous coupled-wave analysis and finite-different time-domain method is applied: the former is used for analyzing the transmission of the structure exactly and the latter is used for acquiring the optical field distribution of the structure. Using the equivalent refractive method, the equivalent mechanical model of the bilayer metallic grating is founded, which is as much of extraordinary optical transmission as the original model, to discover the relationship between the polymer and the s-polarization transmission. The comparison of distribution of field-intensity for two bilayer structures, with or without the polymer, illustrates that the existence of the polymer is the main reason to the s-polarization transmission peak appearance. Because the existence of the polymer can be treated as a waveguide and the s-polarization is coupled by metal grating and then turns to a surface wave, there is a resonant phenomenon occurred in the polymer area under the incident light with particular wavelength. In addition, the effect of geometrical parameters of the polymer, such as the refractive index and the thickness of the polymer, the effect of the thickness of the metal film on s-polarization transmittance are discussed. Increasing the refractive index of the polymer leads to the red shift of transmission peak both in the original bilayer model and the equivalent model, which indicates that the two models have the same property. The transmission peak can be explained by the Fabry-Perot-like resonance, and the red shift of transmission peak is result from the change of the resonance condition due to the refractive index increase. The polymer thickness increase results in the addition of the resonance modes and the corresponding transmission peaks. The cycle of the peak is calculated and the result is similar to the length of the Fabry-Perot-like cavity. However, the thickness of metal layer does not impact the position of the s-polarization transmission peak. In conclusion, the polymer which sustains a waveguide elecromagnetic mode is necessary for the extraordinary optical transmission, and the existence of Fabry-Perot-like resonance in the polymer film is the main reason of the resonant peak appearing.