以啁啾式多層堆疊量子點實現波長可調外腔式雷射

Abstract

本論文主要致力於用分子束磊晶( Molecular Beam Epitaxy , MBE )在砷化鎵( GaAs )基板上成長砷化銦( InAs )以自組式成長( self-assembled growth )的量子點為主動區，並利用改變InGaAs QW覆蓋層( capping layer )的厚度來達成特殊設計的啁啾式多層堆疊量子點雷射( Chirped Multilayer Quantum Dot Laser, CMQD LD )，期望藉由其三種大小量子點的基態與激發態同時雷射的特性，得到一個較為寬廣的增益頻譜特性以作為外腔式雷射光源，得到寬廣的外腔式雷射掃頻波段。 為了得到更為寬廣的波長可調變範圍，我們利用雷射鏡面的抗反射鍍膜來降低其臨界電流以及DBR高反射鍍膜以減少其在雷射另一鏡面產生的多餘鏡面損耗。並設計由光柵零階收光的單邊Littrow外腔式雷射系統，以初步檢測此啁啾式多層堆疊量子點雷射的波長調變潛力。結果顯示其在臨界電流密度0.9 kA/cm2以內的波長調變範圍可從1160 nm至1290 nm，即在低電流密度下其波長調制範圍可達130 nm，且旁模抑制比( SMSR )可達40 dB。

In this thesis, the laser structure is grown by molecular beam epitaxy on n-type GaAs substrate and the active region consists of 10 layers of self-assembled InAs QDs which are capped by InGaAs QWs of varying thickness. Using the specially designed Chirped Multilayer Quantum Dot Laser (CMQD LD) for tunable laser source, we expect to get a broadband gain spectral by simultaneously GS and ES lasing of all these three QD sizes, so as the broad wavelength sweeping range of the external cavity laser. To get a broad wavelength tuning range, we deposited anti-reflection coating on the front facet to increase the initial Fabry-Perot lasers’ threshold current density, and the other facet was deposited with high-reflection DBR coating to reduce mirror loss on this side. And we designed a Littrow configuration external cavity system which the output is composed of the zeroth order grating diffracted light to initially test the potential of this CMQD structure laser. The result shows a tuning range from 1144 nm to 1294 nm (about 150nm) below especially low current density 1.2 kA/cm2, and the side mode suppression ratio (SMSR) is about 40dB.