天線為一種可提高電磁波發射或收集效率的發明。當天線的尺寸小至數百奈米時，其工作頻率可以提升至可見光頻率。可見光電漿奈米天線是近年來科學家積極研究的題目之一，因為它除了提供了機會讓光子取代一般電子做訊號的運算，亦可以在奈米尺寸下增強可見光與物質的作用。如同一般無線電波天線，奈米電漿天線的光學響應與其結構的設計息息相關。在不同光學應用時其所需要的條件皆不同，因此奈米電漿天線的設計是一門重要的研究課題。在此論文中，我們結合理論計算以及光學實驗探討兩種電漿奈米結構的光學特性，同時也研究其具潛力的光學應用。
此論文的第一個研究主題為“電漿都普勒光柵之光學性質解析與環境折射率感測”。電漿都普勒光柵是一個二維的電漿光柵結構，其設計在水平面上呈都普勒效應波前的條紋，因此其光柵周期以及光學響應皆隨著不同方位角而做改變。在論文中，我們詳細探討電漿都普勒光柵的設計原理，同時建構出其光學響應的數學模型。在這之後，我們利用暗場散射光譜技術研究電漿都普勒光柵的光學性質，並且展示其在可見光頻率之篩選，環境折射率感測以及表面增強拉曼光譜上的應用。
此論文的第二個研究主題為“自發光驅動金奈米八木光天線：寬頻指向性奈米可見光源”。在此研究題目中，我們展示如何利用金的螢光自發光來驅動指向性奈米天線，突破一般奈米天線需要以外來螢光光源驅動的限制。利用螢光光譜技術及後焦平面影像技術，我們研究四種不同的金奈米天線螢光自發光的波長與指向性，分別為奈米粒子，奈米八木天線，L型八木奈米天線以及對數週期奈米天線。由於受到電漿共振模態的調控，螢光自發光的波段會隨著天線的共振而做位移，因此它十分適合用來驅動八木天線。利用此光學特性，我們製作出分別可往單方向輻射出650 nm, 800 nm 和 850 nm波長螢光自發光的奈米八目天線。除此之外，我們也首次成功藉由寬頻的螢光自發光驅動對數週期奈米天線。實驗結果顯示，電漿奈米天線除了可以引導電磁波外，天線本身的元件同時也是發光光源。

Inspired by radio-frequency antenna technology, engineering of plasmonic nanoantenna has gain considerable interests in recent years since it provides the opportunities to manipulate the interaction of high-frequency electromagnetic (EM) wave and matter at nanoscale. In this thesis, we present two topic regarding to the control of light and matter interaction using plasmonic nanoantennas.
In the first topic, we present a new design of two dimensional grating with continuous azimuthal angle-dependent periodicity for broadband surface plasmon wave excitation. The Plasmonic Doppler Grating (PDG) consists of a set of non-concentric circular rings that mimics the wavefronts of a moving point source and, therefore, presents azimuthal angle-resolved grating periodicity. The center and span of the working frequency window are fully designable for optimal performance in specific applications. We detail the design, fabrication and optical characterization of the PDG and demonstrate its exemplary applications in azimuthal angle-resolved color sorting, index sensing and surface-enhanced Raman scattering (SERS). We show that broadband source can be sorted continuously into surface plasmons and the variation in surrounding index can be reported as the change of in-plane angle distribution of color. Applications of PDG in grating couplers for silicon photonic circuits, hydrogen sensing, surface plasmon-enhanced spectroscopy and non-linear signal generation are anticipated.
In the second topic, we investigate the driving of directional optical nanoantennas via continuum photoluminescence emission from the gold nanostructures upon laser excitation. By employing photoluminescence (PL) spectroscopy and back-focal plane imaging technique, we study the PL emission wavelength and directivity of four different type gold nanoantennas, which is nanorods, Yagi-Uda (YU) nanoantenna, L-shape Yagi-Uda nanoantenna and log-periodic dipole nanoantenna. We show that the PL emission band always match with the operating wavelength of nanoantennas upon modulation of localized surface plasmon resonance modes, therefore rendering the driving of nanoantenna practical. For example, we shows that three different Yagi-Uda nanoantennas can launch the PL with 650 nm, 800 nm and 850 nm wavelength respectively to a single direction without placing any external quantum emitter near the feed element. Consequently, the PL emission also allow us to experimentally investigate the directivity of broadband log-periodic dipole nanoantenna for the first time. In comparison with the radio-frequency antennas, our results show that the element of optical nanoantennas not only can act as a resonator but also can be a local broadband light source. The PL of gold nanoantennas is an ideal nanoscale unidirectional light source that can be applied in wide field such as high-bandwidth wireless optical communication.

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