量子點雷射之雜訊特性與鎖模特性之研究(I)

Abstract

半導體量子點雷射以自組式量子點為增益介質，由於量子點獨特的物理 特性（類原子能階、空間獨立性）與特殊的材料特性（非均勻展寬大、飽和 增益低、增益回復快），許多新奇的元件特性與新穎的元件應用陸續被提出。 在未來兩年的計畫中，我們將深入研究量子點雷射的雜訊特性與鎖模特性。 NSC99 計劃中將建立半導體雷射之相對雜訊強度的量測技術，完成雜訊 位準的校正，依此萃取量子點雷射的共振頻率與阻尼係數等元件參數，以及 微分增益與非線性增益係數等材料參數。我們將探討基態與激態下雷射發光 的雜訊頻譜，使用可調光濾波器研究雷射縱模之分割雜訊，並配合雷射速率 方程式模擬載子的動態特性。我們也將成長調變摻雜的多層量子點雷射，並 與先前計畫中研製的量子點雷射一併以雜訊頻譜分析其最大頻寬，希望最佳 化磊晶結構與成長條件。 NSC100 計畫中將研究量子點雷射的鎖模特性，我們已於NSC97 中首次 發表砷化鎵基板之單段式電極的自鎖模量子點雷射，因此第二年計畫要探討 單段式電極下自鎖模的優劣程度與操作範圍，並架設二倍頻之自相關干涉儀 來量測脈衝寬度。接著我們將製作兩段式電極偏壓之被動鎖模量子點雷射， 同樣也要決定脈衝光的操作範圍以及各項參數，最終目標希望獲致寬度小於 5 ps，重複頻率超過40 GHz 之高速短光脈衝。

Semiconductor quantum dot (QD) lasers are based on self-assembled growth of QDs as gain medium. Due to their particular physical properties, e.g. spatial localization with atomic-like energy levels, as well as special material properties, e.g. large inhomogeneous broadening, low saturated gain and fast gain recovery, many anomalous device characteristics and novel device applications are published recently. In this two-year project, we will study the noise characteristics and mode-locking properties of QD lasers. In NSC99, the relative intensity noise (RIN) measurement of semiconductor lasers will be setup and its RIN level will be calibrated. From RIN measurement, we could extract device parameters, e.g. resonance frequencies and damping factors, as well as material parameters, e.g. differential gain and nonlinear gain coefficient. We will investigate the noise characteristics between ground-state and excited-state lasing emissions, and study the mode partition noise by tunable optical filter. Multimode laser rate equations will be modeled to confirm the carrier dynamics. We will grow and investigate the modulation-doped QD lasers in this year. Together with those QD laser structures fabricated in previous NSC-Projects, they will be analyzed by RIN measurement to optimize their structure design. In NSC100, we will study the mode-locking properties of QD lasers. As we have published the first self-mode-locking in one-section QD lasers grown on GaAs substrate in NSC97, we will then investigate their completeness and region of self-mode-locking in this one-section configuration. The mode-locked optical pulse will be measured by the new setup of second-harmonic-generation interferometric autocorrelator in this year. We will also fabricate the separately-contacted, two-section QD lasers for passive mode-locking. The locking range and pulse parameters are to be determined as well. Our goal is to achieve high-speed, short optical pulse with pulse width smaller than 5 ps with pulse repetition higher than 40 GHz.