波導模式共振的電光效應

Electro-optical effect on the guided mode resonance

蔡妍葶(Yen-Ting Tsai)

指導教授 ： 黃建璋

國立臺灣大學/電機資訊學院/光電工程學研究所/碩士(2019年)

https://doi.org/10.6342/NTU201903274

摘要

光波導是以光內全反射的機制進行電磁波的傳遞。近年來，光波導被廣泛的應用於濾波器、耦合器、光調制器及衰減器等光通訊的元件上。
在第一部分中我們將光子晶體獨特衍射光學特性與波導模態共振結合，在元件上沉積一層氮化矽薄膜作為導通層，進而將特定波長的光侷限在導通層，在衍射光的頻譜圖上可以觀測到某個波段會有強度下降的現象，此為滿足項為匹配方程式以及滿足於波導的解的結果，因此此現象會對折射率變化更加敏感。在量測的部分也呈現了靈敏度的提升以及更低的量測極限，此元件的靈敏度可以達到每單位折射率產生9173.88奈米的波長變化，且葡萄糖的量測極限達到0.01mM，量測極限範圍達到 〖10〗^(-8) 至 〖10〗^(-9) 的折射率變化，我們的研究結果展示了我們所設計的元件結構以及光學量測分析是非常具有淺力應用於生物感測器當中。
在第二部分中，期望能藉由更多的操作方式來控制光波導感測器，而電是最易取得且容易控制的變因，因此我們將三層對稱型結構的平面光波導施以不同的偏壓，觀察波導的電光效應。並以二氧化矽以及鋰酸鈮作為光波導層，比較線性及非線性材料間的電光效應。兩種材料的波導在施加偏壓後，波長位移及光強度增強同時發生，兩者變化加成形成比一般壓電材料更好的光電特性。而非線性材料的折射率會隨著電壓改變，非線性材料的電光效應較為顯著。不同的入射角度對光波導的電光特性也會產生影響，當入射角度越大時，波長位移越明顯。我們也將兩種材料結合成單一波導層，形成頻寬較窄的光譜，波長的位移以及光強度的變化較單一材料更為明顯，並融合了兩種材料的電光特性，波長位移量達0.85 nm，光強度則隨著電壓由0 V增強至18 V時變化了40%。
我們也結合壓電特性的光波導應用於空氣、水及葡萄糖水溶液等不同折射率的物質感測。結果表明，在0 V時，波導的波長並未隨著待測物的折射率不同而有位移。施加偏壓於元件後，水以及葡萄糖的光強度變化量較空氣明顯，而鋰酸鈮對於不同折射率的待測物較二氧化矽更為靈敏。此部分研究展示了電光材料結合光波導元件應用的可行性。

關鍵字

電光效應 ； 鋰酸鈮 ； 波導共振模態 ； 二維光子晶體 ； 折射率量測

並列摘要

Optical waveguides transverse the E-M waves by the total internal reflection In the past few years, the optical waveguides can be widely applied to optical communication such as filters, couplers, optical modulators and attenuators.
In the first part, we combine the unique optical diffraction characteristics of 2D PhCs with guided mode resonance to further improve sensor performance. The sensor is deposited with a SiNx layer as a guiding layer for limiting light of a particular wavelength. In the diffraction spectrum, we can observe that it has a drop at a specific wavelength. This is the result of satisfying the phase matching condition and being the solution of the waveguide equation. Therefore, this phenomenon is more sensitive to changes in refractive index. It also shows an increase in sensitivity and a lower LOD in the measurement. The sensitivity of the measurement system was calculated to be 9737.88 nm / RIU with a detection limit of 0.01 mM. The range of detection limits in our experiments ranged from 〖10〗^(-8) to 〖10〗^(-9) (RIU). We are very confident that our equipment has excellent biosensor performance for real-time, label-free, and fast detection.
In second part, there are many methods to control the optical waveguides and the electrical power is the most accessible and controllable way. Therefore, the three-layer symmetric optical waveguide is applied under different bias to observe the E-O effect of optical waveguide. Further, we compare the E-O effect between the two optical waveguides fabricated by SiO2 and LiNbO3. After applying bias on them, the wavelength shift and the optical intensity variation can be examined simultaneously, which make the optical properties better than common piezoelectrical materials. LiNbO3 is a nonlinear material of which the refractive index changes with the applied bias, leading to a significant E-O effect. In addition, the incident angle is also a variable of E-O effect. The wavelength shift is more obvious when the corresponding incident angle increases. We also stack two materials as a four-layer symmetric optical waveguide to make the spectrum narrower. The wavelength shifts and the optical intensity variations of the four-layer symmetric optical waveguide are more obvious. In this case, the wavelength shifts about 0.85 nm and the optical intensity varies about 40% as the bias applied from 0V to 18V.
Optical waveguides that possess piezoelectric effect are employed to sense various materials with different refractive index such as, air, water and glucose. The results indicate that guide-mode wavelength is independent of refractive index of target analyte, The change of light intensity is more pronounce in water and glucose compared to the air after applying bias voltage. Furthermore, LiNbO3 has higher sensitivity than SiO2 when detecting refractive index of target. This study suggests the possibility of combining electro-optic material and optical waveguide in further applications.

並列關鍵字

E-O effect ； Lithium niobate ； waveguide resonant mode ； two dimensional photonic crystal ； refractive index measurement

參考文獻

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