The Optical Characteristics Research of GaN-based 2D Photonic Crystal Surface Emitting Lasers
Liu Tzu Wei
|摘要:||本篇論文研究探討氮化鎵二維光子晶體面射型雷射光學特性及回饋式理論。根據理論，在光子晶體周期結構中雷射出射必須滿足布拉格繞射條件。因此，考慮光致發光光譜中心波長425奈米，而設計光子晶體元件之晶格常數範圍190到300奈米。在室溫下，不同元件之雷射的波長範圍395到425奈米。以晶格常數254奈米為例，其線寬約0.19奈米，臨界激發光能量約2.8mJ/cm2。雷射的極化程度和發散角分別為53%及<10度。 其特性溫度大約148K。 我們利用平面波展開法模擬TE能帶圖。從實驗數據研究光子晶體雷射之正規化頻率正好相對於(Γ1，K2，M3) 此三個能帶邊界，表示雷射發生只在特定能帶邊界上。從極化狀態可證實雷射模態確實存在(Γ1，K2，M3)此三個能帶邊緣。藉由二維耦合波模型可決定(Γ1，K2，M3)此三個能帶邊緣的耦合常數。Γ1能帶邊緣有最大耦合常數相對於有最小臨界激發光能量。M3帶邊緣有最小耦合常數相對於有最大臨界激發光能量。氮化鎵光子晶體雷射的優越的光學特性可應用在藍紫外光雷射等高輸出功率之光電元件。|
In this thesis, we investigated the optical characteristics and distributed feedback theory of GaN-based 2D photonic crystal surface emitting lasers (PCSELs). According to the theory, the lasing behavior in the photonic crystal grating structure could only happen as the Bragg condition is satisfied. Therefore, the lattice constant is determined range from 190 to 300 nm considering PL peak centered at a wavelength of 425nm. The lasing wavelength is 395nm to 425nm for different device. We take the lattice constant 254nm for example, which with a linewidth of about 1.9 Å at room temperature. The pumping threshold energy density was estimated to be 2.8 mJ/cm2. Moreover, the degree of polarization and divergent angle of the laser emission is about 53% and smaller than 10o, respectively. The characteristic temperature is about 148K. We use plane wave expansion method (PWEM) to simulate the TE band diagram. All normalized frequency of investigated PC lasing wavelength can correspond to three band-edge frequencies (Γ1, K2, M3), which indicates the lasing action can only occur at specific band-edges. Polarization states confirm the existence of lasing modes at different band-edge (Γ1, K2, M3). The coupling coefficient at different band-edge (Γ1, K2, M3) can be obtained based on 2D couple wave model. The threshold gain at Γ1 is the lowest which corresponds to the highest coupling coefficient while the threshold gain at K3 is the highest which corresponds to the lowest coupling coefficient. Overall, the promising features of GaN-based PCSELs make it become the highly potential optoelectronic device in high power blue-violet emitter applications.
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