雙面光柵波導式生物感測器之光學特性分析

Optical Properties of Biosensors Employing Double-sided Waveguide Grating Couplers

江承桓(Cheng-Huan Chiang)

指導教授 ： 張國恩

國立中正大學/工學院/機械工程學系/碩士(2014年)

摘要

本文以理論及實驗方式探討雙面光柵波導式生物晶片之光學特性分析，項目可分為有限元素模擬、生物晶片穿透實驗、LED穩定性測試三大方向。模擬為利用有限元素軟體Comsol中光波模組進行對雙面光柵波導結構特性及光柵厚度進行耦合效率分析，以釐清影響晶片性能的關鍵參數。接著我們透過生物晶片穿透實驗，利用寬頻白光入射生物晶片，探討在不同入射角度下之最佳入射光源波長及生物晶片穿透特性，並將生物晶片注入待測物溶液糖水探討其共振波長飄移特性。最後探討利用高穩定輸出功率、低成本之LED光源來取代昂貴的雷射當作量測光源之可能性。
在有限元素模擬中得出在光柵結構波導層厚度具有一最佳厚度，當厚度太厚時波導層中會產生第二模態影響靈敏度之線性度，但同時厚度太薄時耦合進波導層之光場將會過小，不利於光訊號之偵測。接著在生物晶片穿透實驗結果發現在不同角度下入射時穿透之波段及穿透率不同。隨後晶片注入待測物糖水中得可以到最佳靈敏度為130nm/RIU，且得知生物晶片在TM mode條件下具有較佳檢測性能。由研究結果得知晶片偵測機制乃為利用光柵表面介質改變而導致穿透光譜隨之變化，未來可發展出以波長飄移為檢測機制之新型生物感測器，並在生物感測、食品安全、以及醫學檢測上能有應用。

關鍵字

生物感測器 ； 波導 ； 雙面光柵

並列摘要

This study theoretically and experimentally analyzes the optical properties of biosensors employing double-sided waveguide grating couplers. Three programs are included in this study: Finite-element simulation, bio-chip’s transmission experiments, and LED stability testing. For simulation, we perform finite-element modeling to investigate the geometry effect of the performance of the biosensors. For the bio-chip transmission experiments, a broadband white light source is incident on bio-chip to obtain the transmission spectra under different incident angles to study the guided-mode resonance properties. By injecting solutions with different refractive indices into biochip, clear shifts of resonance wavelengths are observed. Finally, explore the possibility of using highly stable output power, low cost LEDs as the light source to replace costly lasers in the measurement system for the prospect of mass-production.
From our FEM simulations, it is found that there is an optimal grating thickness where the performance of the biosensors is the highest. When the thickness is too thick, second guided mode in the waveguide appears, resulting in unwanted nonlinear sensitivity curves. On the other hand, the intensity of coupled light becomes too small to detect if the waveguide thickness is too thin. Form the experimental results, the guided mode resonance wavelength is polarization-dependent and changes with different incident angles. Our experiments also show the biosensors have higher performance under TM mode condition and the best sensitivity of the biosensors is ~130nm / RIU. Those results suggest that biosensors using double-sided grating couplers can have important applications in bio-detection, food safety, and medical testing.

並列關鍵字

Waveguide ； Double-sided grating ； Biosensor

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