低損耗次波長混合模態表面電漿子波導之模擬分析

Simulation Analysis of Low Loss Sub-Wavelength Confined Hybrid Surface Plasmonic Polariton Waveguides

朱育葶

指導教授 ： 柳克強

國立清華大學/原子科學院/工程與系統科學系/碩士(2010年)

https://doi.org/10.6843/NTHU.2010.00110

摘要

本論文研究的目地在於藉由模擬來分析表面電漿子波導的混合模態，並進一步改變波導的幾何結構，以期能達到低損耗次波長的研究目標。傳統的電漿子波導在傳遞長度到達100 μm 時，能量局限的範圍已超過1 μm，而利用混合模態來傳遞則可以大大改善此情形。且再更進一步提出新結構，期待在能量傳遞時的能量分布可以更集中，如此將可以在定量的面積上提供更多的波導傳遞。

表面電漿子混合模態是結合表面電漿子模態與介電質模態，使混合模態可以在相對小的限制範圍中傳遞更遠的距離。利用介電質模態所帶來的影響，將能量限制的範圍由金屬移往介電質移動，以減少金屬所產生的損耗。與之前表面電漿子波導所使用的模擬方法不同的是，此研究導入工業界常用的電磁設計軟體HFSS 取代傳統自行寫程式，預期在可接受的誤差內，大量減少研究的入門時間，在未來的研究發展上更容易快速發展出更好的結構。研究初期，先將以HFSS 設計出一裝入預期模擬結構的空腔，改變空腔內波的波數來使其共振頻率座落在期望的通訊頻率上，並將此模擬手法與其他模擬表面電漿子波導的研究團隊的研究結果做比較，確定其間的差距為可接受之範圍。

在確認此模擬手法的可行性之後，首先先改變波導內砷化鎵的形狀，以期能在不減少傳播距離的情況下達到降低製程成本。接著再提出另一於銀基板上挖一溝槽的新結構，希望可以透過結構改變的方式，使能量更為集中，以縮小限制範圍。在進一步更詳細地分析溝槽深度
與寬度對此表面電漿子波導所帶來的影響之後，發現帶有溝槽的新結
構與沒有溝槽的結構相比，的確可以有效地在傳播距離減少小於10 %的情況下，縮小限制範圍於50 %以下。然而由於此結構目前尚屬初步研發階段，期待在未來有更新的結構發展提出，並且配合製程技術的成熟化，更可進一步應用在光積體電路上。

關鍵字

電漿子波導 ； 混合模態

並列摘要

The main purpose of this thesis is to present a new geometric structure for the surface plasmon polariton (SPP) waveguide. In order to have low loss sub-wavelength field confinement, basic ideas for the proposed structure are based on the concepts of hybrid SPP modes that combine typical SPP modes with dielectric waveguide modes. Typical long-range SPP waveguides usually have more than 1 μm mode widths when propagation distances reach about 100 μm. The hybrid SPP waveguide structure have long-range propagation distance with relatively small mode confinement area.

Different from some numerical methods in prior works, this thesis makes use of a methodology operated in HFSS to calculate the hybrid plasmonic guided-wave structures. With eigenmode solver in HFSS, eigenmodes or resonant frequencies of the optical waveguide structures are calculated and key parameters are extracted. This methodology is practiced and confirmed reliable since the simulated results are corresponding to data presented in prior works. With these industrial tool and simulation methodology, time for developing and analyzing new SPP waveguide structures is shortened.

Based on typical hybrid SPP guided-wave structure, the proposed hybrid plasmonic waveguide structure contains an etched channel in silver under the GaAs cylinder. The calculated propagation distance of the proposed waveguide structure reaches about 30 μm with sub-wavelength field confinement. Comparing with typical cylinder based SPP guided-wave structure, the mode area shrinks more than 50% while the propagation distance only decreases only 10%. That is, the proposed hybrid plasmonic waveguide provides comparable propagation distance to typical design while enhancing the field confinement. As advancement of the lithographic micro-processing technology, the proposed optical waveguide structure will have chance to be used in newly optical integrated circuits.

參考文獻

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