• Journals

主編的話

• Journals

Study of Topology Manipulation for Novel Laser Cavity Design

Topology is a property of an object, which is related to its continuity. Any topology transformation needs to involve phase transition or symmetry breaking. Recently, some studies have demonstrated that the topology of the band structure can be manipulated by continuously tuning the geometry. This geometry adjustment leads to the parity transformation at the time-reversal invariant point, changing the topological invariant and achieving the topology manipulation. Notably, when the topology is changed, some novel physics can be induced in this topologically nontrivial system. The scattering-free edge state or interface state appears at the structural boundary. These states have ultra-strong localization and are robust against defects or geometric perturbations, showing great potential for designing the laser cavity and improving the lasing performance. Consequently, to construct an extraordinary laser cavity in the topologically nontrivial system, we propose two ways to manipulate the topology and divide the thesis into two parts. In the first part, strong coupling manipulates band structure topology, enabling off-Γ lasing through Friedrich-Wintgen bound states in the continuum (FWBIC) in a one-dimensional (1D) suspended high contrast grating (HCG). FWBIC exhibits remarkable characteristics, serving as a robust cavity mode for low-threshold performance and tunable lasing directions, vital for high-resolution directional lasing and Lidar applications. Additionally, combining topological and trivial lattices in 1D suspended HCG creates a topological interface state with a small mode volume, reducing lasing thresholds significantly. In the second part, strain-induced synthetic gauge fields manipulate band structure topology by inducing out-of-plane artificial magnetic fields. Photonic topological insulators designed via chiral strain engineering exhibit high-quality topological edge states with short localization lengths, possessing time-reversal symmetry and spin-momentum-locking. These states offer reduced diffraction loss and lossless propagation, even with changing propagation direction, and enable the construction of closed-loop vortex cavities for low-threshold vortex lasing through continuous chiral engineering.

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Coherent Phonon Investigation for Van der Waals Coupling and Photoacoustic Energy Transduction of 2D MoS2 Interfaces

The acoustical behavior of semiconducting transition metal dichalcogenides reflects their mesoscopic properties and determines the heat transfer pathway. Therefore, it plays a crucial role in the design of 2D-based electronics and optoelectronics. In this research, we first applied THz coherent phonon spectroscopy to optically probe the vibrational modes of the epitaxially-grown substrate-supported bi-layer and tri-layer MoS_2, revealing Raman-inactive mode. We extend the linear chain model (LCM) by considering the elastic contact with substrate and next nearest vdWs coupling to analyze the effective spring constants. We further considered the intralayer stiffness as a correction term to acquire the actual interlayer vdWs coupling. Our THz phonon spectroscopy results indicate the interlayer spring constants of 9.03 × 10^(19) N/m^3 and 9.86 × 10^(19) N/m^3 for bi-layer and tri-layer respectively. The second part of this study focuses on van der Waals heterojunctions (vdWHs) consisting of transferred monolayer and bi-layer MoS_2 on a GaN substrate. We observed an asymmetric bipolar acoustic strain wave (~5 ps duration), which describes the surface of substrate undergoing strong compressive deformation after weak tensile deformation in the out-of-plane direction. We developed a theory to explain the mechanisms responsible for the observed strain waveform in the vdWHs elastic system, and obtained the critical parameters of the carrier dynamics. Our results not only report a coherent acoustic phonon generated in the vdWHs, which will complement our understanding of the thermal transfer at the 2D/substrate interface, but also provide information about the intrinsic properties in the vdWHs, which would benefit the design of the 2D-based devices in the future.

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Physics and Applications of Nonlinear Dynamics in Semiconductorlasers Subject to Modulated Optical Injection

This dissertation reports an investigation of the physics of nonlinear dynamics in semiconductor lasers subject to modulated optical injection, focusing on their applications in high-frequency communication, high-resolution radar, and high-speed true physical random number generation. With the use of a semiconductor laser operating in period-one dynamics subject to comb-like modulated optical injection, we achieved stable microwave generation with a 3-dB linewidth below 1 Hz and superior phase noise below -94 dBc/Hz at a 10-kHz offset across the entire V- and W-bands. For communication applications, after a 25-km fiber distribution and 2-m wireless transmission, a bit-error ratio below the 7% hard-decision forward error correction threshold, 3.8 × 10^(-3), was attained for a 96-GHz microwave carrying 12-Gbit/s 16-quadrature amplitude modulation orthogonal frequency division multiplexing data. Furthermore, with the adjustment of the modulation frequency outside the system phase stabilization region, complex dynamics, such as chaotic dynamics, were induced. Accordingly, a chaotic microwave with a broad spectral distribution of more than 50 GHz was generated by injecting an intensity-modulated optical signal into a semiconductor laser. The generated chaotic source improved the range resolution of a time-domain radar system to nearly 1 centimeter and enhanced its anti-jamming capability. Moreover, such a chaotic source was applied to high-speed true physical random number generation with a rate of more than 160 Gbit/s by sending the chaotic source to an analog-to-digital converter for sampling and digitization. The research achievements reported in this dissertation hold the potential to enhance the performance of the Internet of Things technologies.

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垂直共振腔面射型雷射在極端溫度和單模應用的研究

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深度學習應用於光學顯微術之研究

光學顯微鏡藉由鏡頭和光源的組合來觀察微觀尺度的樣本。由於硬體設計和光的物理限制，系統的性能和穩定性會有所不同，有時可能限制系統其應用範圍。如定量微分相位差顯微鏡，配合弱相位轉移函數與Tikhonov正則化，可計算相位分布。此法雖能快速計算定量相位，但對於待測物選擇的侷限性和正則化參數調整的不便，影響了該技術的實用性。而亮場顯微鏡藉由在相機前插入一個微透鏡陣列，以收集更多的角度資訊，使得在相同的數值孔徑下擁有較長的景深。然而，在有限的感光元件上，多角度資訊意味著犧牲影像解析度。基於深度學習方法被廣泛應用於解決逆問題，如相位回推和超解析。近期，一種特殊的深度學習演算法：深度影像先驗被應用於生物醫學影像的計算成像，因為使用這種方法不需要基準真相及大量資料集，可以實現自我監督式學習。論文中，將該演算法結合定量微分相位差顯微鏡和光場顯微鏡，以擴大測物的選擇範圍，免除手動參數調整，並提高空間解析度。

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透過聚合物穩固液晶或動態散射機制製作散射式液晶波導元件

本論文可分為兩大方向，第一部分主要使用液晶波導原理討論扭轉混成型結構之聚合物網絡型液晶盒（Twist-Hybrid Polymer Network Liquid Crystal, TH-PNLC），若利用側向光源饋入施加電場之TH-PNLC液晶盒，由於材料中向列型液晶分子與液晶聚合物折射率產生不匹配，其入射光產生散射並由兩觀測面出射。此時觀察到兩道出射散射光之主要的偏振光分量具有差異，並且利用TH-PNLC結構非對稱特性之散射光製作單向光源液晶元件及隱私保護之應用。第二部分為使用負型液晶摻雜手性分子及離子並利用塗佈有聚乙烯基咔唑（Poly（N-vinylcarbazole），簡稱PVK）薄膜及垂直配向膜之ITO玻璃基板製成液晶盒，透過PVK薄膜能阻絕直流電場及照射紫外光後可形成良好導體的特性，結合液晶動態散射執行圖案化的工作，並透過將側向光源饋入寫上圖案之液晶盒，即可利用液晶波導的原理，進而提高液晶盒整體對比度。

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砷離子佈植於微型發光二極體陣列特性影響之研究

本研究使用藍光磊晶片以雷射直寫曝光技術製作不同像素尺寸相同檯面發光面積（2500 μm^2）的微型發光二極體（micro-light emitting diode, micro-LED）陣列（單一像素尺寸50 X 50 μm^2 1 pixel、單一像素尺寸25 X 25 μm^2 4 pixels、單一像素尺寸10 X 10 μm^2 25 pixels及單一像素尺寸5X5 μm^2 100 pixels），並且比較以砷離子佈植及乾蝕刻製程定義發光區對micro-LED陣列特性之影響。於乾蝕刻定義發光區後使用電漿輔助化學氣相沉積系統（Plasma-Enhanced Chemical Vapor Deposition, PECVD）沉積單層鈍化層（PECVD 525 nm SiO_2）及使用原子層沉積技術（atomic layer deposition, ALD）搭配PECVD沉積雙層鈍化層（ALD 50 nm Al_2O_3/PECVD 525nm SiO_2）進行側壁修復，而砷離子佈植定義發光區製程則無沉積鈍化層，並且三種製程皆於金屬電極蒸鍍製程後進行覆晶貼合（flip chip bonding）並量測micro-LED陣列的電性特性及光電特性，藉以了解不同像素尺寸micro-LED陣列於不同製程下的特性變化及差異。

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低色散／低干擾5G NR毫米波／次兆赫波整合接取系統

隨著全球資訊流量呈爆炸性增長，對於第五代行動通訊的需求迫在眉睫。然而，在5G New Radio（NR）的毫米波／次兆赫波頻段中，由於光纖中同時傳輸多載波會造成色散引起的射頻功率衰減及多載波拍頻引起的信號干擾問題，同時射頻訊號在大氣嚴重衰減等問題，造成無線通訊無法進行長距離傳輸。因此，本研究提出了一套低色散／低干擾的5G NR毫米波／次兆赫波整合接取系統，利用Mach-Zehnder modulator-optoelectronic oscillator（MZM-OEO）的震盪機制與光交織器，產生50 GHz、100 GHz及150 GHz的光載波，並傳送QAM-OFDM訊號，比較多載波與單載波通過光纖的訊號品質。同時，本研究中結合高速無線光通訊技術，克服了市區基地台建設和偏遠地區難以架設基地台的困難，從而提升了網路的覆蓋範圍，實現第五代行動通訊／光纖寬頻／無線光通訊FSO之通訊整合。

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穿透式可撓燭光有機發光二極體

醫學研究證實，藍光容易引起光照視網膜炎等眼疾；夜晚曝照，則會抑制褪黑激素的分泌，導致失眠、糖尿病和心血管等疾病，也會增加罹患乳癌和攝護腺癌的風險。為了回應醫界此等的呼籲，2012年周卓煇博士團隊，發明了燭光有機發光二極體（Organic light emitting diode, OLED）；此一燭光OLED呈現1,800K的色溫；甚至，可以完全移除藍光，有望啟動照明的文藝復興。因此，本研究特別嘗試將燭光OLED，製作在透明、可撓雲母基板上；為了能夠兩面透視，此一元件的上下電極，均必須採用高透光性且具有高導電性的電極材料，此元件可兩面透視，可歸因於使用金屬銀薄膜，替代典型的鋁電極。