光激發式半導體雷射自鎖模現象之研究

Abstract

光激發式半導體雷射(Optically pumped semiconductor lasers)在近年因為雷射商品化的關係，已經成為在產業界被經常使用的雷射光源，其特性因為高功率，頻寬範圍大，目前在各產業上鎖能符合的應用也十分的多，因此我們針對光激發式半導體雷射坐了一系列的測試，希望能對其特性作更深入的分析；然而在測試光激發式半導體雷射的同時，我們發現了其具有自鎖模(self-mode-locked)的現象，因此針對此現象，我們做了深入的研究與探討，希望可以藉由實驗與理論的分析，找出自鎖模形成的原理與機制。 首先我們針對了自鎖模的現象作了完整的紀錄，利用改面不同反射率及曲率的輸出鏡，發現在自鎖模的脈衝寬度與能量會有相對應的變化。接下來的實驗我們將1064nm的基頻光作了倍頻的轉換成為532nm的綠光，並且觀察是否經過倍頻之後仍然有自鎖模的情形，同時也發現了在不同的空間分布上，因為數個高階模態的耦合而產生不同拍頻的頻率，經由理論及模擬的分析，驗證了實驗上所看到的現象。然而自鎖模現象機制仍然沒有被定義出來，從之前的實驗結果發現，高階模態在自鎖模的機制中扮演著很重要的角色，在接下去的實驗中，我們細部的分析出高階模態在自鎖模現象裡所產生的重要關鍵，也證明了自鎖模現象與高階模態有密不可分的關係。

Optically pumped semiconductor lasers have been recognized as well-known laser source for several applications due to its characters of high-power and wide frequency bandwidth. This research used high-power laser diode to be a pumping source and mono¬lithic III-V semiconductor chip contains GaAS layers as gain medium to absorb the IR light alternated with InGaAs quantum wells. In the progress, different values of reflection of output coupler and radius are used as parameters to optimize the laser output power. During the experiment, self-mode-locking was found as a phenomenon in the operating laser system. However, the laser pattern in time domain was observed not a single mode, but coupled with several high order modes and induce to beating in the laser. Further in the research, numerical fitting and theoretical analysis had verified the beating pulse train was induced by high-order modes coupling and high-order modes were playing an important role of starting self-mode-locked operation. Although the mechanism of self-mode-locked operation has not been identified, high-order mode is considered as key element of self-mode-locked operation given by experimental results in this research.