Plasmon Induced Transparency of Three Dimensional U-shaped Nano-resonators

本文主要利用電子束二次對準曝光技術在玻璃基板上製作直立式裂環共振器進行其於可見光以及近紅外線頻段之共振模態分析。首先分析由單一平面以及直立式奈米裂環共振器組成陣列結構的共振模態，發現皆有電偶共振以及磁偶共振兩種模態出現，並將四個直立式裂環共振器組合成一複合結構，證明其可以藉由磁共振模態來互相耦合。接著改變直立式裂環共振器的排列形式，此陣列結構每個單元由三個立體的黃金奈米U型共振環所組成，研究正向入射偏振光與此陣列結構耦合後所產生的遠場穿透率光譜。我們發現到當”工”型單元中間的U型共振環向右邊偏移後(破壞結構的對稱性)，”工”型單元中間的U型共振環之磁場會耦合到另外兩個U型共振環中，造成此陣列結構之遠場穿透率光譜產生出一個特殊的穿透率峰值，並提出一古典RLC電路模型來解釋這個特別的光學現象。Electromagnetically induced transparency (EIT) is a quantum interference effect that reduces light absorption over a narrow spectral region in a coherently driven atomic system. Using electron beam double exposure process, we fabricated erected U-shape nano resonators in an array with 600 nm periodicity both in x and y directions, covering the total area of 75 x 75 μm2 on a fused silica substrate. First, we analyzed the single planar and erected split-ring resonators by experiment and simulation. There are also two resonances including electric and magnetic responses both in the cases of single planar and erected split-ring resonators. We also combined four resonators to make response between each resonator by magnetic resonance. Second, we make three erected U-shape gold nano rings are integrated in a unit cell, in which the height of a gold nano ring is 110 nm. We present experimental as well as numerical simulation results pertaining to plasmonic resonances of erected U-shape gold nano rings under normal illumination. By introducing structural asymmetry, we found the EIT-like spectra in these erected gold nano rings in the case of perpendicular polarized illumination. Finally, a classical RLC circuit model was proposed to explain EIT-like spectra