本研究旨在設計具寬頻、高效率與較短元件長度之 Ta2O5/SiO2 高階模態絕熱耦合器，以實現 TE00 基模至 TE10 高階模態之穩定轉換。首先，透過 supermode 分析設定波導寬度變化範圍，並綜合考量三個代表性波長下之最大絕熱參數 𝐶max、標準差 𝜎 與模態混合判斷指標 𝑅，篩選適合寬頻模態轉換之波導寬度組合。為改善傳統線性絕熱耦合器所需元件長度較長的問題，本研究採用快速準絕熱動態（Fast Quasiadiabatic Dynamics, FAQUAD）重新分配波導沿傳播方向之結構變化速率，使結構於絕熱參數較低處加速演化，並於絕熱參數較高處減緩演化。此外，考量單一波長之 FAQUAD 設計未必能兼顧寬頻操作，本研究進一步導入多波長絕熱工程，同時考1460、1550 與 1600 nm 下之絕熱條件，以降低非絕熱耦合並提升不同波長下的轉換穩定性。模擬結果顯示，經絕熱工程設計後，元件長度可由線性設計之 300 𝜇m縮短至 108 𝜇m約縮短 64%。在 1430 至 1640 nm 的波長範圍內，TE00 至 TE10 的模態轉換效率皆可維持在 90% 以上，顯示所提出之設計可在縮短元件長度的同時，維持寬頻且高效率之高階模態轉換特性。

This study presents a broadband and highly efficient higher-order-mode adiabatic couplerwith a reduced device length based on a Ta2O5/SiO2 waveguide platform. The proposedcoupler is designed to achieve stable mode conversion from the fundamental TE00 modeto the higher-order TE10 mode. First, supermode analysis is performed to determine anappropriate waveguidewidth variation range. The wavelength-averaged maximum adiabatic parameter 𝐶max, its standard deviation 𝜎, and the mode-hybridization indicator 𝑅 atthree representative wavelengths are then jointly considered to select a suitable waveguide-width combination for broadband mode conversion. To overcome the relatively long devicelength required by a conventional linear adiabatic coupler, fast quasiadiabatic dynamics(Fast Quasiadiabatic Dynamics, FAQUAD) is employed to redistribute the rate of structuralvariation along the propagation direction. The waveguide geometry varies more rapidly inregions with a lower adiabatic parameter and more slowly in regions with a higher adiabatic parameter. Since a single-wavelength FAQUAD design may not adequately supportbroadband operation, multiwavelength adiabaticity engineering is further introduced. Thelocal adiabatic conditions at 1460, 1550, and 1600 nm are simultaneously considered toreduce nonadiabatic coupling and improve the consistency of mode conversion at different wavelengths. The simulation results show that, after applying adiabaticity engineering,the device length is reduced from 300 𝜇m for the linear design to 108 𝜇m, correspondingto a reduction of approximately 64%. Over the wavelength range from 1430 to 1640 nm,the TE00-to-TE10 mode-conversion efficiency remains above 90%. These results demonstrate that the proposed design can significantly reduce the required device length whilemaintaining broadband and highly efficient higher-order-mode conversion.

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