多模干涉分光器之改良設計

Abstract

本文探討截角式、加高式、結合式等三種特殊多模干涉一對多(1×N)分光器。所謂截角式是考慮多模波導寬度有變化，加高式是考慮多模波導高度有變化，而結合式則是同時考慮截角與加高兩種變化。模擬結果顯示前兩種變化加在多模波導的入射區時都可以提升多模干涉分光器的傳輸率及減小不均勻度，而且元件的干涉長度也可以縮短；第三種結合式則有兩者加成之效果，其中尤以指數截角加高式為最佳。 為研究上述形狀變化對導光模態的影響，本文以上述之指數截角加高式多模干涉分光器為主，並分別研究其橫向電場模態與橫向磁場模態的傳輸率，結果顯示波導寬度變化僅對橫向電場模態有較為明顯的改善，而波導高度變化則對橫向電場與磁場兩種模態都有明顯的改善。 最後本文又分析一階梯式二維多模干涉分光器。由於其光場有近似之解析解，因此本文提出一優值函數，並調整元件參數使優值函數最佳化，再以此元件參數作為三維光束傳播法模擬之用。模擬結果顯示兩者之誤差範圍約在5%，可以節省許多三維光束傳播法的運算時間。

Multimode interference (MMI) power splitters with various shapes of interference region are analyzed. Simulation results show that a truncated or a raised interference region near the input edge gives rise to higher normalized transmission power, smaller uniformity, and shorter total device length. When the interference region is properly truncated and raised, the improvements can be even better. In particular, MMI power splitter with an exponentially truncated and raised interference region is proposed. Simulation results show that the width modification is sensitive to the filed distributions of transverse electric (TE) modes, but not to those of transverse magnetic (TM) modes. However, the height modification is sensitive to the filed distributions of both TE and TM modes. Finally, approximate field distribution of a 1