單石鎖模半導體量子點雷射

Abstract

半導體量子點雷射以自組式量子點為主動層，由於其獨特的增益與吸收 特性，恰可同時扮演寬頻增益介質與快速飽和吸收器這兩種角色，因此非常 適合應用於雷射鎖模而實現單石半導體量子點鎖模雷射。本年度計畫以 NSC96 提出之啁啾式堆疊量子點為主要結構，輔以主動區的厚度設計及調變 摻雜來研究雷射的鎖模特性。 首先將以前後串接增益區和吸收區之雙區段電極架構來實現被動鎖模， 並研究兩區段之操作條件對鎖模範圍的影響，期能研製出脈衝重複頻率超過 50 GHz 且脈衝寬度小於5 ps 之超快雷射；其次將探討單區段電極架構之超長 （> 1.5 cm）共振腔的自鎖模與主動鎖模，並以擬購置的自相關光干涉儀來量 測分析雷射鎖模下之光脈衝特性，包含脈衝寬度、脈衝重複頻率與脈衝時序 顫動等；最後將以乾式蝕刻DBR 反射鏡製作微共振腔（< 50 μm）之量子點 雷射，評估量子點鎖模雷射實現兆赫波輻射的可行性，我們將先觀測單區段 電極是否可以獲致兆赫波段的自鎖模，然後思考製程上如何研製雙區段電極 之兆赫波段的被動鎖模。

Semiconductor quantum dot (QD) lasers are based on self-assembled growth of QDs as gain medium. Their unique gain and absorption characteristics, which facilitate them simultaneously used as broadband gain medium and as fast saturable absorber, thus well suited for mode-locking applications. It is therefore very promising to investigate semiconductor mode-locked lasers monolithically implemented with QD gain medium. In this proposal, the mode-locking properties of QD lasers will be studied mainly based on our chirpy-stacked QD structure proposed in NSC96. The dependence of mode-locking on the layer design, such as layer thickness and modulation doping, will also be studied. First, passively mode-locked QD lasers will be fabricated by tandem configuration of gain and saturable absorption sections. The locking range will be determined in terms of gain current and reverse bias. The goal is to achieve ultrafast QD lasers with pulse repetition higher than 50 GHz and pulse width smaller than 5 ps. Then, the self-mode-locking as well as active mode-locking of single-section configuration with ultra-long cavity (> 1.5 cm) will be studied. The pulse parameters, such as pulse width, repetition rate, and timing jitter, will also be measured and analyzed by our proposed purchase of optical autocorrelator. Finally, edge-emitting QD microlasers with cavity length shorter than 50 μm will be fabricated with dry-etched DBR mirrors. The feasibility study of terahertz radiation by QD mode-locked lasers from such a short cavity will be carried out. We have to check if terahertz self-mode-locking could be observed in single-cavity configuration. Moreover, we should try to solve the processing difficulties to achieve terahertz passive mode-locking in tandem section configuration.