基於一維光學結構之旋光隔絕器、電漿子奈米雷射及藕合式感測器

Abstract

光子的利用和光學控制在光子積體電路應用中是至關重要的。在本論文中, 我們探究具潛力應用於光子積體電路之中的元件，包括由一維光學結構組成之光學隔絕器、奈米雷射和感測器。在論文的第一部分，我們利用理論分析一個架構於強導波的旋光光子晶體波導之上的光學隔絕器。在保持互易性的系統中，旋光波導的傳導模態雖然對於許多散射體並不敏感，但並非完全無背向散射的。因之，我們利用第一階玻恩假設及藕合模態理論來推導致使強背向散射的規則，並利用其結論來歸納避免強反射的條件。論文的第二部分，因致力於產生及感應光子的半導體光學元件具有尺寸微小化的趨勢，而較小的元件更擁有節能及省材料的優勢；而要達到元件微小化，其中一個方式，便是在結構上利用金屬材料使光子和表面電漿藕合形成表面電漿極子，達成超越繞射極限的目標。為了實現同調奈米尺度光源，我們分析了在通訊波段下由金屬奈米線所組成的奈米共振腔及其中的藕合表面電漿間隔模態，並研究其在厚覆蓋層下的效應。在一定折射率區間的覆蓋層材料選擇下，基礎的藕合電漿間隔模態是較有可能產生雷射的模態；不同的是，在高折射率的的覆蓋層材料包覆下，第一階波導模態較有潛力產生雷射。然而，不論在那一種模態的操作中，鏡面的損耗更是雷射的首要挑戰。故，我們在共振腔兩端被覆銀的鏡面，可使得反射率大幅提升，共振腔的品質因子也因之提高，致使雷射模態的產生成為可能。論文的第三部分考慮作為感測器的用途，利用光子晶體來控制光子，並結合電漿極子的藕合，來操控光子於更微小的尺度下。我們藉之提出了一個奈米共振腔，其具有靠近金屬基板的一個混合電漿極子-光子晶體的矽奈米線。當週期性刻槽製作於奈米線上，此結構具有完全的一維光子能隙。更者，我們把一個極小缺陷引入週期性的結構來侷限奈米尺度的光場，所形成之奈米共振腔的結構具有很高的品質因子與模態體積之比值，可引致很強的光與物質交互作用。我們相信此利用由下而上製程方式來製作的奈米共振腔，未來可應用於無標記式的生物檢測及實現單晶片實驗室元件的目的。

The photon manipulation and optical control are essential for photonic integrated circuits. In this dissertation, we look into isolators, nanolasers, and sensors which are made up of one-dimensional photonic structures and may play advanced roles therein. We begin by theoretically analyzing an optical isolator based on strongly-guided chiral photonic-crystal waveguides. Without breaking the reciprocity, the propagating modes in this chiral waveguide are not backscattering-immune even though they are insensitive to many types of scatters. We use the first-order Born approximation and coupled-mode theory to unfold the rules of strong backscattering. The criteria required to avoid the backscattering in this chiral structure will be worked out. On the generation and sensing of photons, semiconductor-based photonic devices tend to follow the path toward miniaturization. The smaller devices could be more energy-efficient or material-saving. By mixing photons with surface plasmons into polaritons, metals provide a way to overcome the diffraction limit. To reach coherent nanoscale photon sources, we analytically examine plasmonic gap-mode nanocavities consisting of metallic nanowires (NWRs) at telecommunication wavelengths. We investigate the covering effect of thick cladding on the plasmonic cavity. Within a certain index range of the cladding, the fundamental hybrid plasmonic mode is the most promising lasing mode. However, in the presence of high-index cladding materials, the lasing action of the first-order gap mode is more favorable. In both cases, the mirror loss is the main challenge to lasing. With silver coatings at two end facets, the reflectivity is substantially enhanced, and a decent quality (Q) factor for the lasing mode is achievable. On the sensing side, the combination of photonic crystals (PhCs) and plasmonics could bring about the manipulation of photons at the extremely small scale. We accordingly proposed a hybrid plasmonic-PhC nanocavity composed of silicon NWRs near the metal surface. Periodic corrugations are imposed on the NWR. Such hybrid periodic structures can support a complete one-dimensional bandgap. A defect structure is further introduced into the NWR PhC to confine the optical energy in the nanoscale. The nanocavity has a high ratio between the Q factor and modal volume and can boost the light-matter interaction. The high sensitivity and Q factor are also present as immersed in aqueous solutions. This structure could function as label-free biosensors in lab-on-a-chip devices based on the bottom-up technology.