| 摘要: | 近年來光子晶體共振腔由於具有極小元件體積、高Purcell效應且高結構調變性，可望被用在光通訊或單光子發射器等應用上。但光子晶體應用於光通訊及光學電路上，勢必要提高其輸出功率，而光子晶體陣列可有效的提高輸出功率，其中光子晶體陣列的耦合效應造成的共振模態變化則是影響輸出功率的一大因素。本研究採用具有極低模態體積、高Purcell效應及較少共振模態的quasi-L2光子晶體共振腔分析耦合效應對共振模態的影響，可更進一步調變多重共振腔及共振腔陣列的排列角度及距離，探討共振腔間的交互作用及共振模態的變化，可望作為光通訊或光學電路的光源。
根據模擬結果，雙重共振腔因耦合效應會產生兩個耦合共振模態，分別為電場同相震盪及反向震盪的模態，由於模態消散波以30?方向由共振腔中心往外傳遞，因此30?方向的耦合效應不隨共振腔間距增加而急遽減弱。三重共振腔因耦合效應會產生三個共振模態，若共振腔以不同角度排列，則只能觀察到耦合效應最強兩共振腔的耦合共振模態，較弱的耦合效應則會被抑制，若共振腔以相同角度排列，則三個共振腔皆會相互耦合共振。而共振腔陣列則分為0?和90?組成的矩形陣列及30?組成的菱形陣列，矩形陣列只有耦合效應最強的兩共振腔會相互耦合，但菱形陣列則是四個共振腔皆會相互耦合共振。藉由動量空間分析，菱形陣列的垂直方向侷限能力較佳。菱形陣列除了可使共振腔間達到較穩定的耦合效應，控制所有共振腔的震盪相位以達到同相位共振，且亦能保有良好的侷限能力及Purcell效應。
實驗上本研究觀察到不同幾何排列的雙重共振腔模態分裂量趨勢與模擬吻合，且30?方向的耦合效應隨共振腔間距增加仍可觀察到耦合效應。由雙重共振腔的模擬結果可驗證共振腔的耦合效應與模擬吻合，因此我們可藉由調變共振腔的排列以改變共振腔間的耦合效應及共振模態。而共振腔陣列的模態分佈與模擬吻合，因此可預期共振腔間的耦合效應與模擬推測相同。共振腔陣列應以30?方向排列使所有共振腔皆耦合共振，可藉由耦合效應控制所有共振腔皆以同相位共振，且可操作在高輸出功率的模態，此研究結果可提供光子晶體陣列幾何結構的設計參考。
In recent years, photonic crystal (PhC) nanocavities have inspired great interest in on-chip interconnection or single photon source because of small mode volume, high Purcell effect, low threshold power, and high structure controllability. However, the low output power of PhC nanocavity limits the application for fiber communication, and the PhC array has been proposed to overcome this bottleneck. Moreover, the coupling effect is an important factor for array output power. In this research, the effects of cavity separation and permutation angle on coupling effect and resonant modes of quasi-L2 cavity were investigated.
According to simulation results, the fundamental mode would split into bonding mode and anti-bonding mode in double cavity. The mode splitting of 30o direction coupling is less dependent on cavity separation, because the evanescent wave of fundamental mode propagates along 30o direction. In triple cavity cases, the light would be confined at the strongest coupling cavities. As the cavity arranged at same permutation angle, all cavities would couple to each other. The PhC array separates from square array and rhombus array. In the square array, light would only be confined in the strongest cavities. In the rhombus array, all cavities would couple to each other. According to momentum analysis, the rhombus array has better vertical confinement than square array. So the rhombus array could achieve strong coupling between cavities and keep good confinement.
According to experimental results, we observed the mode splitting fits with simulation results. As increasing cavity separation, we still could observe mode splitting at 30o coupling direction. And the PhC array mode splitting measurement results also fits with simulation result. So the coupling effect is fits with simulation analysis. The best permutation of PhC nanocavity array is 30o direction, which could keep all cavities coupling, in-phase resonating, and high output power mode operation. These results could provide a design standard of PhC array geometry structure. |
