超穎材料結構之光學應用研究

Metamaterial Structures for Optical Applications

陳則安(Tse-An Chen)

指導教授 ： 嚴大任

國立清華大學/工學院/材料科學工程學系/博士(2021年)

摘要

近年來，超穎材料被廣泛的運用在光電領域。藉由選用的材料以及經過設計的次波長週期結構，可精準的調控電磁波的偏振、振幅與相位等特性。隨著微影製程技術的成熟，無塵室製程可以輕易地製作出奈米元件，這也增廣了超材料的應用，例如完美吸收體、超穎透鏡、全像投影等等。
第一個研究主題是利用電漿子能帶理論解析之雙曲超材料，雙曲超材料具有特別的電磁特性，可實現廣泛的應用，例如超分辨率和自發輻射。在預測和分析雙曲超材料的這些光學特性時，大多數研究人員採用有效介質理論。然而，該理論僅適用於長波長和無限堆疊層。為了探測表面狀態並驗證光學拓撲轉變，我們製作了由MgF2/Ag 交互堆疊而成的多層膜雙曲超材料。我們所有的分析、數值計算和實驗測量表明，多層膜雙曲超材料的表面態色散曲線上的“過渡點” 僅取決於金屬層和介電層的厚度比。這的預測結果較傳統的有效介質理論準確。電漿子能帶理論的結果提供了更準確的預測，並可利用於的雙曲超材料的應用。
第二個研究主題是超寬頻類黑體完美吸收體，過去幾年，電漿子共振的完美吸收體廣泛的運用在各種應用，例如生物感測器、非線性光學、濾波器和熱發射器。大多數的電漿子完美吸收體都是藉由電子束微影所製作而成，然而，電子束微影成本高昂，限制了這些設備的大規模生產和實際應用性。因此，我們提出了一個多層膜的結構，不需要藉由微影製程就可製作的結構。此多層膜可以同時再横磁模式以及横電模式近乎完美吸收波長900奈米到1900奈米的光。此外，此結構對於入射角度有很高的容忍度，在入射角小於70度時，可以吸收80%以上的電磁波。換句話說，我們成功的開發出一個寬頻且對於任意極化角以及任意入射角均可以完美吸收的類黑體完美吸收體。
第三個研究主題是惠更斯超穎平面光偏折元件，在這項工作中，我們提出了由二氧化鈦奈米圓盤陣列組成的超穎介面。首先，材料的選擇，二氧化鈦有優異的高介電常數 (εreal≅ 6) 和低損耗 (εimag≅ 0)適合運用在此工作波段。藉由重疊奈米圓盤的電和磁共振以同時實現100%的穿透以及完整的 2π 相位。在本論文中，超穎介面構成的惠更斯模擬達近90%的穿透率。在實驗上，惠更斯超穎介面來穿透率和以及光偏折效率，分別為 80% 和 15%。我們相信，所提議的惠更斯超穎平面光偏折元件將成為平面光學設備的新典範，包括超透鏡、全息和光束整形設備。

關鍵字

超穎材料 ； 雙曲面超材料 ； 完美吸收體 ； 會更斯超穎介面

並列摘要

In recent years, metamaterials have been widely used in the field of optoelectronics. With the selected materials and the designed sub-wavelength periodic structure, the polarization, amplitude, and phase characteristics of electromagnetic waves can be precisely controlled. With the maturity of the lithography process technology, nano-components can be easily produced by the clean room process, which also expands the application of metamaterials, such as perfect absorbers, meta lenses, holographic projection, and so on.
The first research topic is “the plasmonic band structure theory for 1D-HMMs”. Hyperbolic metamaterials (HMMs) possess marvelous and considerable applications: hyperlens, spontaneous emission engineering and nonlinear optics. Conventionally, effective medium theory, which is only valid for long wavelength limit, was used to predict and analyze the optical properties and applications. In our previous works, we considered a binary 1DHMM which consists of alternative metallic and dielectric layers, and rigorously demonstrated the existence of surface states and bulk-interface correspondence with the plasmonic band theory from the coupled surface plasmon point of view. In the plasmonic band structure, we can classify 1DHMMs into two classes: metallic-like and dielectric-like, depending on the formation of the surface states with dielectric and metallic material, respectively. Band crossing exists only when the dielectric layers are thicker than the metallic ones, which is independent from the dielectric constants. Furthermore, the 1DHMMs are all metallic-like without band crossing. On the other hand, the 1DHMMs with band crossing are metal-like before the band crossing point, while they are dielectric-like after the band crossing point. In this work, we measure the surface states formed by dielectric material and 1DHMMs with band crossing in Otto configuration. With white light source and sweeping the incident angle, we measure the reflectance to investigate the existence of the surface states of 1DHMMs with various thickness ratio of metallic to dielectric layers. Conclusively, we can clear observe the transition point via experimental set up. The disappearance of the surface states indicates the topological phase transition of 1DHMMs. Our experimental results will benefit new applications for manipulating light on the surface of hyperbolic metamaterials.
The second research topic is “Ultra-broadband blackbody-like perfect absorber”. Perfect absorbers based on enabled by plasmonic resonance are attracting interest for various applications, such as biosensors, nonlinearity, filters, and thermal emitters. However, electron beam (EB) lithography is often used to fabricate such devices. EB lithography is costly, which places limits on the mass production and practical application of these devices. We have designed a perfect broadband absorber with impressive oblique angle tolerance. Its multilayered structure consists of magnesium fluoride (MgF2) and chromium (Cr) layers, and device fabrication does not require EB lithography. The device absorbs more than 90% of light in the 900–1900-nm range. Ultra-broadband absorption is unaffected by the polarization and incidence angle of light up to 70°. The performance of the optimized device is in good agreement with predictions based on the transfer matrix method (TMM) calculations and Comsol Multiphysics 5.3a simulations. Thin-film coatings are of considerable importance for the realization of high-performance planar blackbody infrared absorbers, and our simple design is practical for industrial production.
The third research topic is “Huygens’ surface based light bending device”. We proposed an all-dielectric Huygens’ metasurface composed of TiO2 nano-disks and consequently constructed a beam bending device through the metasurface for the demonstration of phase manipulation within near-UV regime. First of all, the titanium dioxide was chosen due to its superior high dielectric constant (εreal≅ 6) and low losses (εimag≅ 0) compared to other candidates, for example, aluminum or silicon in this frequency range. Then, the near-UV Huygens’ metasurface is realized by spectrally overlapping nano-disks’ electric and magnetic resonances of the equal amplitudes to achieve unity transmission and a full 2π phase coverage, simultaneously. Finally, the near-UV all-dielectric Huygens’ metasurface are employed to experimentally realize unity transmittance and beam-bending with an experimental efficiency of 80% and 15 %, respectively. We believe that the proposed near-UV all-dielectric Huygens’ metasurfaces would be a new paragon for flat optical devices, including metalenses, holography and beam-shaping devices.

並列關鍵字

Metamaterials ； Hyperbolic Metamaterials ； Perfect Absorber ； Huygens' Surface

參考文獻

(1) Poddubny, A.; Iorsh, I.; Belov, P.; Kivshar, Y. Hyperbolic metamaterials. Nature Photonics 2013, 7 (12), 948-957, DOI: 10.1038/nphoton.2013.243.

(2) Ferrari, L.; Lu, D.; Lepage, D.; Liu, Z. Enhanced spontaneous emission inside hyperbolic metamaterials. Opt. Express 2014, 22 (4), 4301-4306, DOI: 10.1364/OE.22.004301.

(3) Lu, D.; Kan, J. J.; Fullerton, E. E.; Liu, Z. Enhancing spontaneous emission rates of molecules using nanopatterned multilayer hyperbolic metamaterials. Nature Nanotechnology 2014, 9, 48, DOI: 10.1038/nnano.2013.276

(4) Roth, D. J.; Krasavin, A. V.; Wade, A.; Dickson, W.; Murphy, A.; Kéna-Cohen, S.; Pollard, R.; Wurtz, G. A.; Richards, D.; Maier, S. A.; Zayats, A. V. Spontaneous Emission inside a Hyperbolic Metamaterial Waveguide. ACS Photonics 2017, 4 (10), 2513-2521, DOI: 10.1021/acsphotonics.7b00767.

(5) Shen, K.-C.; Hsieh, C.; Cheng, Y.-J.; Tsai, D. P. Giant enhancement of emission efficiency and light directivity by using hyperbolic metacavity on deep-ultraviolet AlGaN emitter. Nano Energy 2018, 45, 353-358, DOI: https://doi.org/10.1016/j.nanoen.2018.01.020.