可應用於折射率感測器的高Q值表面模態二維光子晶體板緣共振腔之研究

Abstract

由於超小的模態體積，利用二維光子晶體共振腔應用於折射率感測器，可以比其他光學方法所製作的感應器能偵測更小的範圍。為了獲得更高的感測度與最小的可偵測折射係數，在本論文中我們首先討論典型的二維光子晶體板緣共振腔，這種板緣共振腔最大特色就是將模態聚集在表面而容易達到高感測度，利用此特性並且藉由調變不同的切面比例以及透過三維有限時域差分法，我們可以計算此共振腔的Q值與感測度。為了更進一步最佳化Q值，我們設計了異質結構的板緣共振腔，利用其模態能隙的原理，可以較平緩地將模態聚集在共振腔內，因此大幅提升了Q值，並且也降低了其所對應最小的可偵測折射係數值。

接著用半導體製程方法將實際元件製作出來，並利用共焦顯微螢光光譜系統來量測基本的雷射特性。此外並且架設氣體真空腔系統，透過注入純二氧化碳與改變不同的氣壓，來調變此元件所處的環境折射係數，經由共焦顯微螢光光譜系統來觀察共振波長的位移，以此來計算感測度與最小可偵測折射係數值，最後將量測結果討論與分析。

The two-dimensional photonic crystal microcavity could be applied for refractive index sensing, which could detect the smaller region than another optical method due to the ultra-small mode volume. In order to obtain the higher sensitivity and smaller detectable resolution of refractive index, in this thesis, first we discuss typical two-dimensional slab-edge-mode microcavity. The merit of this type microcavity is the mode concentrating in the surface and easily to obtain high sensitivity. From this characteristic, we apply 3D finite-difference time-domain method to simulate the quality (Q) factor and sensitivity by varied different truncated facets. In order to further optimize the Q factor, we demonstrate hetero-slab-edge microcavities. The electric field is confined gently by mode-gap effect, therefore the Q factor is increasing suddenly, and the minimum detectable refractive index is also decreasing.

And we fabricate the real device by a series of fabrication processes. The basic lasing characters are measured by micro-PL system. In addition, we build a gas chamber to change the device environment refractive index by controlling the different pressure of carbon dioxide. The sensitivity and minimum detectable refractive index could be calculated by this experiment. Finally, we will discuss and analysis these results.