利用光柵耦合的被動鎖模量子點雷射達成在1.3微米波段波長可調且低重複率的超短脈衝光源

Abstract

本論文利用光柵耦合的兩段式J型波導量子點雷射，作為多功能的連續波或短脈衝光源。在兩段波導皆為相同的順向偏壓操作時，其功用為波長可調的單模態連續波光源，利用光柵選擇，在1.3μm波段範圍成功達成140nm的連續調變範圍，其範圍涵蓋量子點基態與激發態的發光頻寬，光譜半高寬皆小於0.1nm，且具有40dB的旁模抑制比；在其中一段波導逆向偏壓作為飽和吸收體時，其為被動鎖模的脈衝雷射，其波長在基態與激發態可調變波長範圍分別為33nm與30nm，脈衝寬度在10~30ps範圍，藉由調整外部共振腔長度，其脈衝重複率可由2GHz到87.2MHz連續調變，其中87.2MHz為目前文獻上被動鎖模半導體雷射所能達到的最低頻率，有利於後續的光強度放大與生醫影像的應用。

In this thesis, an external grating-coupled two-section J-shape waveguide quantum dot device was used as a multi-functional light source. The wavelength tuning range was over 140nm in 1.3 μm range when the two sections were shorted and in the same forward bias. The lasing wavelength can be continuously tuned from the ground state to the excited state of the quantum dots, while the linewidth was smaller than 0.1 nm, and the side mode suppression ratio (SMSR) is about 40 dB. When one of the two sections was reversely biased as a saturable absorber, the laser was passively mode-locked. The tuning range of the lasing wavelength was about 33 nm and 30 nm for the ground state and the excited state, respectively. The pulsewidth depended on the injection current and the absorber bias and was varied from 10 ps to 30 ps. With changing the length of the external cavity, the repetition rate was continuously tuned from 2 GHz to 87.2 MHz. To the best of our knowledge, the repetition rate of 87.2 MHz was the lowest frequency achieved to date for any passively mode-locked semiconductor laser, which can make major contribution to medical and bio-imaging applications.