基於石墨晶格光子晶體Γ點能帶邊緣模態的多功能發光元件

Abstract

光子能帶邊緣模態操作於晶格對稱點附近光子能帶較平坦的區域，利用其慢光效應以增強光與增益介質的交互作用，從而達到雷射操作。在這些晶格對稱點中，位於Γ點的能帶邊緣模態由於在水平方向波向量分量接近於零，使得元件具有垂直面射型發光的特性。在此篇論文中，我們利用石墨晶格中位於不同Γ點的能帶邊緣模態，成功實現出一個多功能的發光元件。相較於常見的三角或正方晶格，石墨晶格由於大量減少空氣孔洞的密度，所以具有保留較多增益介質與較佳散熱效果等優點。 首先，我們利用三維平面波展開法模擬石墨晶格光子晶體的光子能帶圖，並分析了各模態的電場分佈。在實驗量測上，具不同晶格常數的元件利用一連串的半導體製程技術所製造。經由量測不同Γ點能帶邊緣模態的發光特性，包括單極 (Γ2), 雙極 (Γ4,5), 與四極 (Γ6,7) 模態被進一步的分析。在室溫環境下，我們分別於單極與四極模態的量測中都觀察到單一雷射模態操作。當中單極模態具有大於 30 dB的高旁模壓抑比(SMSR)，此優點十分適合於光通訊系統中作為訊號源的應用。另外經由注入已知折射系數的有機溶液，我們量測了不同環境下的雷射頻譜，發現四極模態可以達到375 nm/RIU 的高感測靈敏度。此一結果顯示出四極模態在生醫感測應用上的潛力。除此之外，我們發現雙極模態雖然沒有達到雷射操作，但具有大約5倍光激發光的增強以及100 nm寬頻寬等特點，使得雙極模態有利於製造高亮度的發光二極體。

Photonic band-edge mode utilizes the flat photonic band near lattice symmetry point, enhances light-gain interaction and achieves lasing operation due to the slow light effect. Among those symmetry points, band-edge mode near Γ-point with almost zero in-plane wave vector component favor for directional surface emission. In this thesis, we successfully demonstrated a multi-functional light emitter based on band-edge modes near Γ-point of graphite lattice in two-dimensional photonic crystal slab. Compare to typical triangular or square lattice, graphite lattice with reduced air hole density leads to larger gain volume and better heat dissipation. At first, the photonic band diagram and related band-edge mode profiles of graphite lattice are simulated and characterized by 3D plane-wave-expansion method. And real devices with different lattice constant are fabricated by series of semiconductor fabrication process. By measuring the optical properties of band-edge modes near different Γ-point, including the monopole (Γ2), dipole (Γ4,5), and quadrupole (Γ6,7) modes. We observed single mode lasing action from monopole and quadrupole modes at room temperature respectively. The monopole mode with high side-mode suppression-ratio of 30 dB shows its ability for optical micro-laser application. And quadrupole mode exhibit high index sensitivity of 375 nm/RIU by the measuring lasing spectra with different index match liquid, show its potential in refractive index sensor for biochemical detection. Besides these two lasing modes, over five-fold photoluminescence enhancement with broad band-width of 100 nm from the dipole mode is also observed, which is promising in realize high brightness light-emitting-diodes.