| 摘要: | 本研究致力於研製出薄膜鈮酸鋰（Lithium Niobate-on-Insulator，LNOI）為基礎之波導元件，並且利用其材料特性達到低損耗、高折射率對比使得元件長度能進一步變得更加緊湊。透過 LNOI 與異質材料之結合，可有效放大結構設計上的自由度，進一步提升元件整體效能。
模擬上採用x-cut LNOI進行設計，利用RSoft光學軟體中的光束傳播方法(Beam propagation method，BPM)進行分析，首先會模擬出雷射光源進入至脊型波導(Rib Waveguide)的傳輸情形，接著進一步模擬和分析出絕熱耦合器(Adiabatic Coupler，AC)結構，以實現偏振態的有效分離。再進一步透過氮化矽(Silicon Nitride)之異質材料整合，優化出的被動元件將實現高寬頻（high broadband）的偏振模態分光器(Polarizing Mode Splitter，PMS)。
實驗上使用半導體相關設備進行黃光、微影、薄膜鍍膜、乾式蝕刻等技術進行實驗，透過跨區域型的製作來整合達成目標。其主要蝕刻波導使用的機器為感應耦合電漿反應離子蝕刻(Inductively Coupled Plasma-Reactive ion etching，ICP RIE)進行波導蝕刻，成功做出脊型波導並且把蝕刻過後的剩餘殘留物(Redepositions)進行完整移除，確保波導側壁與傳輸損耗的有效降低。
在未來，結合本實驗室所發展之鈮酸鋰材料極化反轉（poling）技術，可進一步引入非線性光學現象，使該元件不僅具備偏振操控能力，亦能實現波長轉換、糾纏光子產生與量子態操控等功能，拓展至量子光學與量子量測相關應用。透過精確設計的波導結構與極化區域分佈，在同一晶片上整合偏振分離、非線性轉換，提升量子系統的整體穩定度。藉由優化異質材料波導幾何，未來可針對更寬操作頻譜與更高製程容忍度進行設計，提升元件在實際製程與系統應用中的可靠度。此發展將有助於建構出量子積體光路（Quantum Photonic Integrated Circuits，QPICs）平台。;This thesis focuses on the development of waveguide devices based on lithium niobate on insulator (LNOI). By utilizing the material properties of LNOI, including low optical loss and high refractive index contrast, the device length can be further reduced, enabling more compact integrated structures. In addition, the combination of LNOI with heterogeneous materials provides greater flexibility in structural design and improves overall device performance.
In the simulation stage, x-cut LNOI is used as the substrate material. The optical characteristics are analyzed using the beam propagation method (BPM) implemented in the RSoft optical simulation software. First, the propagation behavior of a laser source in a rib waveguide is simulated. An adiabatic coupler (AC) structure is then designed and analyzed to achieve effective separation of different polarization states. Furthermore, by integrating silicon nitride (SiN) as a heterogeneous material, the passive device is optimized to realize a high-broadband polarization mode splitter (PMS).
For the fabrication process, standard semiconductor microfabrication techniques, including photolithography, thin-film deposition, and dry etching, are employed. A cross-region integration approach is adopted to complete the device fabrication. The waveguides are mainly etched using inductively coupled plasma reactive ion etching (ICP-RIE), successfully forming rib waveguide structures. Redeposition residues generated during the etching process are effectively removed, ensuring improved sidewall quality and reduced propagation loss.
In future work, by combining the electric-field poling technique for lithium niobate developed in our laboratory, nonlinear optical effects can be introduced into the proposed devices. This allows the devices to support wavelength conversion, entangled photon generation, and quantum state manipulation, extending their applications to quantum optics and quantum measurement. Through precise design of waveguide structures and poling region distributions, polarization separation and nonlinear optical functions can be integrated on a single chip, improving system stability. Further optimization of heterogeneous waveguide geometries is expected to enable broader operating bandwidths and higher fabrication tolerance, contributing to the development of quantum photonic integrated circuits (QPICs). |
