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標題: | 局域性表面電漿子紅外線奈米光子元件之製作與應用 Preparation and applications of localized surface plasmon polariton based infrared nanophotonic devices |
作者: | Cheng-Wen Cheng 鄭程文 |
指導教授: | 施閔雄(Min-Hsiung Shih),陳智泓(Chyh-Hong Chern) |
關鍵字: | 金屬,局域性表面電漿子,熱輻射器,吸收器,偏振片,折射率感測器, metals,localized surface plasmon polaritons,thermal emitters,absorbers,polarizers,index sensors, |
出版年 : | 2012 |
學位: | 博士 |
摘要: | 在本論文中,我們利用表面電漿子和局域性表面電漿子的光學獨特性,在理論和實驗上展示一些主動與被動表面電漿元件,例如窄頻寬熱輻射器、與入射角和偏振無關紅外線濾波/吸收器、全向性紅外線偏振片和高性能折射率感測器。
根據克希荷夫熱輻射定律,利用金屬圓形碟盤結構,我們製作出一個高效率紅外線窄頻寬熱輻射器。對於TE與TM入射偏振光而言,此圓形結構具有一個局域性表面電漿子模態。此模態造成一個無偏振性窄頻寬熱輻射峰,其輻射波長與頻寬為4.27μm和0.25μm. 其窄頻寬、下邊帶、高強度熱輻射特性,可應用在紅外線熱輻射光源。 關於應用在光學上的濾波/吸收器,我們通常需要高入射角度容忍度。不過,大多報告過的濾波/吸收器的濾波品質都與入射角度有關。在本文第四章,我們展示一個T型陣列結構製作在銀/二氧化矽/銀基板上,其結構具有一個與入射角度無關的表面電漿子模態。此結構可做為一個無入射角限制之反射式帶止濾波/吸收元件,應用在紅外線波段。藉由改變此結構幾何,其濾波頻帶位置可被調控。無入射角限制的特點,使此T型結構濾波元件設計,更加靈活彈性於光學波導模態共振濾波元件、表面電漿子濾波元件和多層表面電漿結構濾波元件。為了提升其元件吸收特性和降低製程技術困難,我們提出一個金屬圓形碟盤結構陣列,並具有一條局域性表面電漿子能帶,其入射角容許值接近達90度。有別於之前研究結果,我們實驗與嚴格耦合波理論模擬結果顯示,此局域性表面電漿子共振波長與圓形碟盤周期無關。利用與周期無關的特性,我們製作出一個大頻寬的紅外線吸收器,頻寬可到2000nm。我們又發現調變圓形碟盤與單位晶胞面積比,一個高性能、廣角、無偏振性的雙波段吸收器可被實現,在寬廣入射角範圍下,其吸收器最大兩個吸收峰值可超過84%。此結果,可靈活運用在吸收器設計,特別是在熱光電元件、感測器和偽裝等用途。 除了,金屬圓形碟盤結構陣列在第三與第四章所提的吸收與輻射特性外,我們發現改變碟盤結構的長短軸比,其TE和TM共振峰可分開。因此,金屬橢圓形碟盤結構可以濾掉TE或TM反射光,做為一個便宜的全向性紅外線偏振片。在實驗上,使用碟盤結構長短軸比0.65,發現極化率99%在波長4.12μm為TE共振模態和91%在5.25μm為TM共振模態,其實驗結果與模擬一致。TM與TE共振模態消光比各為20dB和15dB,藉由調變結構長短軸比,此消光比可進一步提高。 在最後第六章,我們利用橢圓碟盤陣列在蝕刻二氧化矽層的結構,成功製作出一個高性能表面電漿子折射率感測器,運作波長範圍從1000nm到1800nm。感測器的靈敏度和品質因子各為691nm/RIU和2.5,此靈敏度和品質因子數值,為目前為止近紅外線波段最高記錄。在本章中,我們會介紹一個新的概念有效提升其感測性能。此感測概念,有助維持局域性表面電漿子感測器性能。在將來工作中,我們與中央研究院應科中心董奕鐘教授合作,將靶細胞放在此元件上,做為細胞偵測用途。 在附錄A和B,我們將介紹可調變表面電漿子能隙和感應光電壓在金光柵上的基礎性研究。根據上述T型陣列結構,當我們增加在二氧化矽夾層的金屬柱狀長度,表面電漿子能隙會存在出現。此能隙並非由額外半周期光柵造成,而是由於金屬-金屬和單層金屬折射率對比造成的。其能隙大小與金屬柱狀長度呈線性正比。此結構可廣範應用在能隙波導和缺陷共振腔雷射/發射器。 在附錄B,我們與美國Boise State大學Wan Kuang教授合作,研究在金光柵上的感應光電壓。我們利用半古典電磁模型和弱非線性近似,來描述金光柵上的感應光電壓。此模型利用有限元素法來模擬並與量測結果比較。模擬感應光電壓是入射角和波長的函數,與我們實驗結果符合。此結果,提供一條描述更加詳細,研究光子-電子交互作用在元件上的路。 In the thesis with the unique properties of surface plasmon polaritons (SPPs) and localized surface plasmon polaritons (LSPPs), a number of active and passive surface plasmon-based elements on chips were demonstrated numerically and experimentally, such as a narrow-band thermal emitter, wide-angle polarization independent infrared filters/absorbers, an omni-directional mid-infrared polarizer, and a high-performance index sensor. Based on the Kirchhoff’s law of thermal radiation with a round-shaped metal disk array, we demonstrated an efficient narrow-band thermal emitter in the MIR region. The structure exhibits one significant LSPP mode for both TM and TE polarizations, leading to an un-polarized narrow emission peak observed at 4.27μm with a FWHM of 0.25μm. This kind of emission property with narrow bandwidth, low sideband and high intensity is very useful for the application in IR light sources. For the applications in optical filters/absorber, large incident angle tolerance is always in demand. However, most of reported filters/absorbers are angle-dependent. In chapter 4, we demonstrated a T-shaped array in Ag/SiO2/Ag platform, showing an angle-independent LSPP mode. The structure can be as an angle-independent reflection-type band-stop filter/absorber in mid-infrared (MIR) region. The stop-band can also be adjusted by varying the structure geometry. The angle-independent feature makes the designed filter more flexible than a guided-mode resonance dielectric filter and a SPP filter as well as a plasmonic multilayer filter. To further improve the absorption performance and reduce the fabrication difficulty, a round-shaped metal disk array is applied because it has a LSPP band over a broad range of incidence angles of up to nearly 90°. Different from the previous work of the round-shaped metal disk array, our experimental results and numerical simulations performed by using rigorous coupled-wave analysis (RCWA) clearly revealed that the resonant wavelength of the LSPP band is independent of the disk periodicity. Based on the periodic independent result, a broadband absorber with a bandwidth 2000nm operating at MIR region can be realized. We also found that by manipulating the disk area ratios per unit cell (ie area fill factors) and disk sizes, a high-performance, wide-angle, polarization-independent dual band absorber with two maximal absorptivity peaks greater than 84% over a wide of range of incident angles was experimentally achieved. The results demonstrated a substantial flexibility in absorber designs for applications in thermal photovoltaics, sensors, and camouflage. In addition to the absorption and emission properties of the round-shaped disk structure in chapter 3 and chapter 4, we found that by tuning the aspect ratio b/a of the disk structure, both angle-independent TE- and TM- polarized resonant peaks can be separated. Therefore, the oval-shaped disk based structure can filter out completely one component of the light polarization and reflects perfectly the other component of the light polarization as a cheap omni-directional mid-IR polarizer. In our experiments, we found that such structure with b/a=0.65 (a=1543nm, b=1009nm) has a degree of polarization 91% at wavelength 4.12μm for TE mode and 99% at 5.25μm for TM mode, showing a good agreement with our simulation. The extinction ratios for both TM and TE modes are 20dB and 15dB, all of which can be further improved by tailoring the b/a axial ratio. In the last chapter 6, based on the oval-shaped disk array structure with the SiO2 layer etching, a highly performance plsmonic index sensor operating at wavelengths from 1000nm to 1800nm can be realized. The sensitivity 691nm/RIU and FOM=2.5 can be achieved as the highest record up to now in the NIR region. In the chapter, we also introduce a novel concept for the improvement in plasmonic sensing. The sensing strategy based on the concept can offer great potential to maintain the performance of LSPP sensors. In the future work, we will cooperate with Professor Yi-Chung Tung at RCAS, Academic Sinica to produce target cells on such device for the cell detection. In Appendix A and B, fundamental studies of a tunable SPP band gap and photon induced voltage on an Au grating slab are introduced, respectively. Based on the T-shaped structure with the post under the top grating, a SPP band gap in Appendix A, can occur without using extra periodic grating Λg/2 when the post length is increased. The SPP band gap is attributed to the index contract between the metal-metal and single metal regions, and is linearly proportional to the post length. Such a T-shaped structure with a tunable LSPP band gap can be widely exploited in various applications, such as band gap waveguides and defect cavity lasers/emitters. In Appendix B, we cooperated with professor Wan Kuang’s group at Boise State University, USA to study photon induced voltage on an Au grating slab. A semi-classical electrodynamic model is developed for the Au grating slab under the weak nonlinearity approximation. The model was solved by finite element method and compared with our measurements. The calculated photon induced voltage as a function of incident angles and wavelengths was found to be in qualitatively agreement with the experimental measurements, giving a pathway for the study of devices with more detailed photon electron interactions. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/6864 |
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