半導體雷射激發光纖雷射系統之物理與技術

Abstract

本文主要使用雙包層之摻鐿及鉺鐿共摻之大模態光纖(摻鐿光纖之纖核直徑:30μm，鉺鐿共摻光纖之纖核直徑:25μm)作為研究雷射二極體激發之高功率光纖雷射的特性。首先我們使用窄頻寬的薄膜濾光片作為控制雷射縱模之元件，完成了波長可調且窄波段的的光纖雷射; 之後則建立了被動式及被動式的Q開關光纖雷射。在被動式Q開關中，首先是使用摻鐿之光纖作為增益介質。我們分別使用Cr:YAG晶體以及半導體材料AlGaInAs作為飽和吸收體。在以Cr4+:YAG晶體作為飽和吸收體的實驗中可得到脈衝能量為350 μJ;在以半導體作為飽和吸收體 的實驗中，實驗結果其可操作在5~30 kHz且脈衝能量約為 450 μJ。另外在使用鉺鐿共摻光纖作為增益介質的實驗中，我們亦利用同樣材料的半導體但比例不同而使其吸收波段在1.5 μm來作為飽和吸收體。結果在13.5 W的激發功率之下可得到平均功率為1.26 W，脈衝能量為100μJ及重覆率為12 kHz輸出。主動式Q開關光纖雷射中我們採用聲光晶體來產生腔內的損耗，我們測試了幾種不同的方法來 增加聲光晶體的調變損耗以提升脈衝波能量。實驗結果可得到600 μJ的脈衝能量及42ns的脈衝寬度。

An Yb doped large-mode-area (LMA) fiber with a core diameter of 30 μm and an inner cladding diameter of 250 μm, and an Er/Yb codoped fiber with a core diameter of 25 μm and an inner cladding diameter of 300 μm have been used for researching in development of high power fiber lasers. Firstly we demonstrated tunable and narrow linewidth Yb and Er/Yb fiber lasers by use of thin film narrowband filters. Afterwards we have demonstrated passively and actively Q-switched fiber lasers. By use of Yb doped fiber as the gain medium, we have obtained passively Q-switched fiber lasers by employing a Cr4+:YAG crystal and an AlGaInAs semiconductor material as saturable absorbers respectively. The results revealed that with a Cr:YAG as a saturable absorber in a diode-pumped Yb fiber laser, the laser could generate a pulse energy of 350 μJ at a repetition rate of 38 kHz. For the use of AlGaInAs based saturable absorber experiment, we have realized a pulsed laser with 450-μJ pulse energy and can be operated at pulse repetition rate of 5~30kHz. The pulse train is very stable of ~10% fluctuation. Besides, we also obtained a passively Q-switched Er/Yb codoped fiber by means of another AlGaInAs semiconductor saturable absorber. Greater than 0.1 mJ of pulse energy at a repetition rate of 12 kHz was generated. Finally in the actively Q-switched fiber lasers, by enhancing the loss modulation of the active Q-switch (acoustic-optical modulator), we have obtained pulse of 600-μJ pulse energy and 42-ns pulse width.