探討包含金屬之非對稱、單一位能障壁系統中輻射模態致發之共振光學穿隧;On the Radiation-Mode-Enabled Resonant Optical Tunneling in Asymmetric, Single Barrier Potential System with Metal

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题名:	探討包含金屬之非對稱、單一位能障壁系統中輻射模態致發之共振光學穿隧;On the Radiation-Mode-Enabled Resonant Optical Tunneling in Asymmetric, Single Barrier Potential System with Metal
作者:	陳宇桓;Chen,Yu-huan
贡献者:	光電科學與工程學系
关键词:	共振;光學穿隧;輻射模態;Resonance;Optical tunneling;Radiation mode
日期:	2014-08-28
上传时间:	2014-10-15 14:45:18 (UTC+8)
出版者:	國立中央大學
摘要:	本論文探討在包含金屬之非對稱位能障壁系統中輻射模態致發之共振光學穿隧現象，以波長633 nm之橫向電場(transverse electric, TE)極化之電磁波在接近臨界角(critical angle)之角度入射由BK7玻璃、銀金屬、二氧化鈦所組成之非對稱結構，可以得到超過70% 之穿透率。將分別從光學以及量子力學兩方面討論共振光學穿隧。以理論計算穿透率對於不同入射角度、結構之關係以及計算於結構中累積之相位改變，結果顯示高穿透率之現象為輻射模態致發之共振光學穿隧現象。而在計算頻率對光學穿隧之影響，發現穿透率峰值隨頻率而改變，以入射頻率為328.29 THz或473.9 THz之穿透率峰值為中心，頻率升高或降低皆會導致穿透率峰值下降。由Fabry-Perot諧振腔模型，可以得知在低頻時，由於銀金屬與二氧化鈦層之介面反射率隨頻率降低而下降，共振效應降低，造成穿透峰值下降。而在高頻時，電磁波通過銀金屬薄膜之穿透率隨頻率升高而下降，進入共振腔內之電磁波減少，造成穿透峰值之降低。而以量子力學觀點來討論，頻率提高時，對波長歸一化之位能障礙寬度隨之提高，使得粒子進入共振腔機率下降，穿透率降低。反之，位能障礙寬度隨頻率降低，反射回入射區域之粒子機率提高，於輸出區域找到粒子機率相對降低。實驗驗證部分，設計實驗架設量取穿透率與反射率角度頻譜以驗證共振光學穿隧現象，並分析樣品製程誤差對實驗結果之影響。 ;Radiation-mode-enabled resonant optical tunneling in asymmetric, single barrier potential system with metal is investigated. The system consists of BK7 glass/silver (Ag)/titanium dioxide (TiO2)/air with the silver as the tunnel barrier. High transmittance (up to >70%) is shown to occur with transverse-electric wave incidence at near critical angle and a wavelength of 633 nm. Using finite-element-method-based simulation shows that the high transmittance - is -due to the excitation of a radiation mode of the geometry. Unlike ordinary resonator, the transmittance peaks at 328.2 and 473.9 THz in the frequency spectrum and decreases toward lower and higher frequencies. At lower frequencies, the reflectance at Ag-TiO2 interface decreases as the frequency is decreased which, from the Fabry-Perot model, weakens the resonance and leads to a lower transmittance. The decrease in transmittance as the frequency is increased is due to a low transmittance through the Ag layer , which reduces the field amplitudes penetrating into the TiO2 cavity. In the anology of quantum mechanics, the barrier thickness (normalized to wavelength) increases with the increasing frequency, which lowers the tunneling probability (i.e. transmittance) for a particle to penetrate into the cavity. On the other hand, decreasing frequency causes thinner normalized barrier thickness which would lower the confinement capability on the tunnel barrier side and increase the reflection probability back to the incident region. Experimental demonstration is pursued but to no avail due largely to sample preparations that require a small fabrication tolerance of <±1.7 nm.
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