半導體量子點兆赫波輻射源之研製

Abstract

半導體自組式量子點具有獨特的材料與物理特性，近年後受到廣泛研究 而開發出多項優異元件及新穎應用，如量子點超高亮度二極體之寬頻光源、 鎖模量子點雷射之短脈衝光源以及外腔式量子點雷射之可調光源等。而兆赫 波段輻射源雖然有許多潛在應用，長久以來受到電學與光學限制而有兆赫波 間隙，我們相信這是量子點增益介質可以大展身手的舞台。 本計劃以NSC96 所提出的數位啁啾式堆疊量子點結構為基礎，延續 NSC98 執行波長可調外腔式量子點雷射以及NSC100 執行鎖模量子點雷射的 經驗。在今年的計劃提案，第一階段要把鎖模量子點雷射的共振腔長度縮短 至150 μm 以下，推升脈衝重複率進入兆赫波段；我們將探討單區段自鎖模與 雙區段被動鎖模這兩種電極架構，磊晶部份以最佳化的多層堆疊量子點結構 來增加光模增益，製程部分則結合乾式蝕刻與介電質蒸鍍之布拉格反射鏡來 降低鏡面損耗。第二階段為達成兆赫波段輻射源的頻率可調，我們以微機電 之數位微型反射鏡元件來實作雙雷射波長之外腔式量子點雷射，其雷射線寬 及差頻範圍應可滿足設計需求，最後利用非線性光學的差頻產生機制來實現 全兆赫波段的頻率皆可調之輻射源。

The unique material and physics properties of semiconductor self-assembled quantum dots (QDs) are intensively investigated in recent years; therefore many superior devices and novel applications are developed, such as QD superluminescent diodes for broadband light sources, mode-locked QD lasers for short-pulse light sources, as well as external-cavity QD lasers for tunable light sources. Despite many potential applications adhered to terahertz radiations, there are so-called terahertz gap due to original limitation of electronic and photonic devices. We believe it is the QD gain media that can take role to make a breakthrough. This project will be carried out based on the digitally chirpy-stacked QD structure proposed in NSC96 as well as the experiences accumulated in NSC98 of wavelength tunable external-cavity QD lasers and NSC100 of mode-locked QD lasers. In the first stage, we will reduce cavity lengths of mode-locked QD lasers down to 150 μm so that pulse repetition rate can increase up to terahertz range. Both single-section and two-section biasing configurations will be investigated. Epitaxial multilayer QD structure will be optimized to increase the optical modal gain, while dry-etched and dielectric-coated distributed Bragg reflectors will be incorporated to reduce the mirror losses. In the second stage, dual-wavelength and tunable external-cavity QD lasers will be realized by MEMS-based digital micromirror device. The linewidth and frequency difference of these two lasing wavelengths are suitable for terahertz generation. Tunable emission radiations through the full terahertz range can therefore be achieved by nonlinear optical mechanism of difference frequency generation.