- 學位論文
牛眼光波穿透結構之電磁分析
Electromagnetics Study of Bull's-Eye Structures for Optical-Wave Transmission
摘要
本文之研究重點在於開發一種具有多重異常穿透波峰現象與多重指向性出射現象之牛眼(光波穿透)結構。為了達到上述目的，本文設計了一種新式牛眼結構，該結構之形成方式敘述如下。首先，吾人在金屬銀薄膜上做出一個次波長孔徑，然後將混週期凹槽結構刻劃在銀薄膜之金屬表面，並讓這些混週期凹槽環繞前述之次波長孔徑，繼而獲得本研究所提出之新式牛眼結構—混週期式牛眼結構。此處所提出之混週期凹槽結構，乃是指經由兩組週期性凹槽結構疊加後所形成之混合結構。 接著，吾人使用自行開發之二維及三維平行化有限差分時域法軟體，針對混週期式牛眼結構的電磁光波現象進行探討。本研究之數值分析結果表明，當光波穿透過混週期式牛眼結構上之次波長孔徑時，出射光會出現類似於舊式牛眼結構(此指刻劃週期性凹槽之牛眼結構)所擁有之異常穿透現象及指向性出射現象。具體而言，當混週期凹槽刻劃在銀薄膜的光入射面時，由於表面電漿共振激發，此牛眼結構之出射光的穿透頻譜圖會出現多重異常穿透波峰；反之，當混週期凹槽轉為刻劃在銀薄膜的光出射面時，由於表面電漿子之繞射效應，出射光的場形分佈圖會出現多重指向性出射現象，即出射光會形成兩道不對稱或者對稱之準直光束。此外，上述之數值模擬結果亦與表面電漿子光柵繞射理論所預測之結果相當穩合。 綜上所述，由於本文所提出之混週期式牛眼結構不僅具有多波長濾波特性，同時亦具有產生不對稱或對稱型態之分光特性，因此本研究之結論認為，混週期式牛眼結構在微型濾波元件及微型分光元件之發展上極具應用潛力，可提供吾人在微觀尺度下操控光路更大的自由度。
並列摘要
The aim of this dissertation research is to study how to utilize the bull's-eye structure to produce multiple peaks for the extraordinary optical transmission (EOT) phenomenon and multiple beams for the beaming phenomenon. For the purpose of realizing multiple-peak and multiple-beam phenomena, we have used the mixedperiod grooves to surround a single subwavelength slit to form the mixed-periodbull's- eye (MPBE) and investigated the interaction between the incident light and the MPBE. Here the mixed-period grooves refer to a set of grooves arranged with particular groove pitches, which are formed by merging two sets of periodic grooves with similar geometries but mainly different groove periodicities. Also, we have developed a finite-difference time-domain (FDTD) method based simulator with parallel computing for modelling the electromagnetic phenomena generated by the MPBE. Based on the FDTD simulation, we have successfully demonstrated that the multiple-peak EOT phenomenon and the multiple-beam beaming phenomenon can be produced by the MPBE. In addition, the numerical results given by the FDTD method are consistent with the theoretical results given by the surface plasmon polariton (SPP) diffraction theory. Moreover, we have applied the idea for the mixed-period grooves to the twodimensional (2-D) bull's-eye, namely, a single subwavelength hole surrounded by concentric annular grooves, to form a 2-D MPBE. Our FDTD simulation results show that the 2-D MPBE also exhibits multiple EOT peaks. Based on the numerical results given is this work, we believe that the presented MPBE will have potential applications in compact photinic devices such as multiple-peak optical filters and miniatured optical beam-splitters.