基於連續譜中準束縛態之窄頻高靈敏度折射率感測器

Abstract

本論文研究在玻璃基板上設計具有非對稱性的週期性奈米結構陣列，激發其連續光譜中的準束縛態，探討樣品在不同的環境折射率下所產生的共振位移特性，成功實現高靈敏度之近紅外波段感測器。此結構由兩個不對稱的非晶矽(Amorphous silicon，a-Si)長方柱所組成，通過改變成對奈米長方柱的旋轉角來破壞結構的平面對稱性，以激發連續光譜中的準束縛態，同時具環形磁偶極矩和電四極矩共振特徵，並在局部環境的折射量測到具有超高靈敏度變化。本文從模擬計算深入探討結構基於不同的旋轉角度，高度與壁直對共振光譜所產生的影響，並探討藉由模擬增加材料損耗k時不同旋轉角度下的頻譜差異，再利用電子束微影製程製作樣品。在靈敏度的測試上，我們分別在樣品上旋塗三種不同折射率的材料，在結構高度為450 nm下，實驗與模擬測得之靈敏度和品質因數達到608 nm/RIU和46與612 nm/RIU和85。本論文研究之連續譜中基於準束縛態的高品質因子生物感測器利用介電材料之奈米結構在穿透光譜中有特徵共振，隨著環境折射率不同而位移，造成穿透光譜中特徵共振位移及環境折射率改變之特性，故可應用於偵測氣體與液體之生物感測，亦或者可以利用radiation continuum中的BIC作為完美濾波器。

This thesis studies the design of asymmnetric periodic nanostructures on glass substrates to excite the quasi bound state in the continuum (Q-BIC), investigates the resonant shift characteristics of the samples under different ambient refractive indices, and successfully realize the high sensitivity BIC sensors working in the near-infrared. The structure is composed of two asymmetric amorphous silicon (a-Si) nanorod pairs. By rotating the tilted angle of nanobar pairs, a Q-BIC mode was excited due to the breaking of in-plane symmetry and shows a dominant toroidal dipole (TD) and electric quadrupole (EQ) resonant feature with ultrahigh sensitivity in the refractometric monitoring of local environment changes. We first numerically studied the geometric effect of the structural rotation angle, height, and the straightness of the side-wall on the spectra as well as the inclusion of the extinction coefficient to the materials. Then, the sample were fabricated by the electron-beam lithography process. For the test of sensitivity, three different media were spin-coated on the top of the samples, and the measured (simulated) sensitivity and figure of merit for nanobar pairs with a height of 450 nm reaches 608 nm/RIU and 46 (612 nm/RIU and 85). The high quality factor biosensor based on quasi-bound state in the continuum studied in this thesis utilizes the nanostructure of dielectric materials to have characteristic resonance in the transmission spectrum, which shifts with the difference of the refractive index of the environment, resulting in the characteristic resonance in the transmission spectrum. The characteristic resonance shift and the change of the refractive index of the environment can be applied to biological sensing of gas and liquid, or can use the BIC in the radiation continuum as the perfect filter.