| 摘要: | 隨著AI與數據中心的增加，資料傳輸的密度也隨之提升，此時選用矽光晶片成為一個優選方案。矽光晶片的優勢在於比電訊號擁有更大的頻寬，且更為節能。在製程方面，由於元件的物理特性，在量產製程大多使用i-line或DUV即可製作。為了能同時傳輸多組波長訊號以增加通訊密度，矽光晶片中的波長分波多工(Wavelength Division Multiplexing, WDM)系統變得至關重要。矽光晶片中的WDM系統通常使用馬赫曾德爾干涉儀(Mach-Zehnder interferometer, MZI)或環形共振腔作為多工器(Multiplexer, MUX)或解多工器(Demultiplexer, DEMUX)器件。環形共振腔本身擁有高密度佈局與窄雷射線寬的優勢，因此本論文將環形共振腔作為研究元件。由於WDM系統中的最窄通道間距僅25GHz (0.2nm)，環形共振腔如果產生過多的模態或過寬的波長線寬，都會導致訊號之間發生干擾。
為此，本論文展示了使用非對稱環形共振腔達成高階模態抑制及相對較高的本質品質因子結構設計。當中也驗證了在不改變直波導與環形波導間距下如何提高元件耦合係數。理論分析表明，如果要獲得較高的多模抑制能力，縮小環形波導的寬度是最直接的方法，但這也會間接增加散射損耗。若要獲得較高的品質因子，就必須增加環寬，減少模態與波導側壁的交互作用，但這同時也會導致波導中存在高階模態。
為了實現最佳的性能平衡，本研究探討了非對稱環寬設計對元件性能的影響。首先本論文透過RSoft FullWAVE FDTD 模擬設計出了1μm至3μm做漸進變化的非對稱環型波導，其中也包含了對照組的設計，分別為1μm均勻環寬波導及3μm均勻環寬波導。這些設計均選用氮化矽材料來製作波導結構。經量測實驗後， 數據顯示出本質品質因子的趨勢為3μm環寬 > 非對稱環 > 1μm環寬。結果顯示，非對稱環寬結構在保持高階模態抑制的同時，也實現了比1μm環寬更高的本質品質因子，證明了此設計在多模態抑制與本質品質因子之間的良好平衡。此外，本論文也實現透過調整環波導結構，使非對稱環型共振腔接近於臨界耦合。
;With the increasing prevalence of AI and data centers, data transmission density has also risen, making silicon photonics an optimal choice. Silicon photonics offer greater bandwidth than electrical signals and are more energy-efficient. In terms of fabrication, due to the physical characteristics of the components, production processes mostly utilize i-line or DUV lithography for mass production. The Wavelength Division Multiplexing (WDM) systems within silicon photonics become crucial for transmitting multiple wavelength signals simultaneously to enhance communication density. Typically, WDM systems in silicon photonics employ Mach-Zehnder interferometers (MZI) or ring resonators as multiplexers or demultiplexers. The ring resonators themselves benefit from high-density integration and narrow linewidths, making them ideal for this study.
This thesis focuses on utilizing asymmetric ring resonators to achieve high-order mode suppression and higher intrinsic quality factor (Qi-factor) structural design. It also verifies how to enhance the coupling coefficient of components without altering the gap between straight waveguides and ring waveguides. Theoretical analysis indicates that narrowing the width of the ring waveguide is the most direct method to achieve better multi-mode suppression, albeit at the cost of increased scattering losses. Conversely, to achieve higher Qi-factors, widening the ring reduces interactions between modes and waveguide sidewalls, though this may induce higher-order modes into the waveguide.
To achieve an optimal balance of performance, this research investigates the impact of asymmetric ring width designs on component performance. The paper initially designs asymmetric ring waveguides ranging from 1μm to 3μm with gradual variation using RSoft FullWAVE FDTD simulations. Uniform ring counterparts are also included for comparison: a 1μm uniform ring width waveguide and a 3μm uniform ring width waveguide, all fabricated using silicon nitride material. Experimental measurements indicate that the trend in intrinsic Q-factor is 3μm uniform ring > Asymmetric > 1μm uniform ring. The results demonstrate that asymmetric ring width structures achieve a higher Qi-factor than 1μm uniform ring designs while maintaining effective suppression of higher-order modes, highlighting a favorable balance between multi-mode suppression and Qi-factor.
Additionally, this thesis also demonstrates that by adjusting the ring waveguide structure, the asymmetric ring resonator can be brought close to critical coupling. |
