光柵結構下的表面電漿磁光柯爾增強效應

Enhanced Magneto-optical Kerr Effects on Surface Plasmonic Grating

林恩平(EN-PING LIN)

指導教授 ： 李明昌

國立清華大學/電機資訊學院/光電工程研究所/碩士(2012年)

摘要

基於表面電漿子(Surface Plasmon Polariton, SPP)的特性，將其用於生物感測用途的研究被廣泛討論，而與磁光效應(Magneto-optical effect)的合併運用更可以增強元件的檢測靈敏度。
本論文中將元件設計為金(Au)/鐵(Fe)/金(Au)三層的光柵耦合式結構，基於金的低光學吸收以及鐵的高磁導率特性，在提升表面電漿耦合效率的同時也能提供明顯的磁光效應。本實驗所採用的光柵耦合式結構非但能夠屏除傳統的表面電漿所使用的耦合稜鏡，並能夠在正向入射的條件下使入射光耦合進表面電漿，有利於使整體的光學架設精簡化。有別於一般稜鏡耦合式將消逝波耦合進結構背面的現象，光柵耦合式能將表面電漿消逝波耦合至光柵上方，並能夠大幅度減少消逝波被鐵磁性材料吸收的機會。基於上述的特性，本實驗中所設計的元件能夠增加鐵磁性材料的厚度以提升材料的磁導率，進而使的磁光效應更加明顯。
實驗結果證實了在表面電漿耦合波段處確實有磁光訊號增強的現象，而其靈敏度比一般的光柵耦合式要大上1.7倍，而本次實驗中所設計的金(Au)/鐵(Fe)/金(Au)三層光柵耦合式結構的靈敏度也比一般的金(Au)/鐵(Fe)/金(Au)三層稜鏡耦合式要大上4倍。

關鍵字

表面電漿 ； 磁光效應 ； 表面電漿生物感測器 ； 鐵磁性材料

並列摘要

Surface plasmonic polariton (SPP) for the use of bio-sensing has been widely studied. In this thesis, SPP combined with magneto-optical effect is used for enhancing the sensitivity of the device.
We designed a sub-wavelength grating structure made from Au/Fe/Au composite layers simultaneously achieving the advantage of low optical absorption of gold and high permeability characteristics of iron. The grating structure used in this experiment not only can be able to remove the prism which the conventional surface plasmon sensor requires but also satisfy the conditions of surface plasmon coupling in normal incident situation. Unlike the general prism setup that the SPP is coupled from the back side of structure, the grating coupler can be able to excite the SPP wave on the top of the grating and reduced the absorption of surface plasmon from ferromagnetic material. Based on these characteristics, the structure designed in this thesis can increase the thickness of ferromagnetic material to improve the magnetization without inducing more absorption and enhanced the magneto-optical signal significantly.
The experimental results agree well with the analysis of magneto-optical signal enhanced by SPP near the surface plasmon resonance wavelength. The estimated sensitivity of our structure is 1.7 times larger than the grating coupler without including the magneto-optical effect. And the sensitivity of Au/Fe/Au SPP grating coupler designed in our experiment is 4 times larger than the Au/Fe/Au SPP sensor through prism couplers.

並列關鍵字

Surface plasmon ； Magneto-optical effect ； SPR biosensor ； ferromagnetic material

參考文獻

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