利用聲光調變器產生穩定Q開關鎖模摻鐿光纖雷射之研究

Abstract

在本論文中，我們藉由聲光調變器和線性光纖共振腔在摻鐿的光纖雷射系統中達到穩定的Q開關鎖模雷射運作。在Q開關的封包內，我們觀察到鎖模脈衝的重複頻率為40 MHz，與聲光調變器內部聲波的頻率相同。在實驗上，我們也發現Q波包的寬度與對稱性取決於聲光調變器外加的調變頻率。當外加頻率變低的時候，我們觀察到Q開關的波包有衛星脈衝的產生，而且它的數目也與外加的調變頻率有關係。藉由改變在聲光晶體上的光束大小，我們證明了鎖模脈衝的啟動機制是由聲光調變器振幅調變的作用所產生之諧波鎖模。

In this thesis, reliable Q-switched mode-locking in an Yb-doped fiber laser is demonstrated by employing an acousto-optic modulator (AOM) and a linear fiber cavity. Within the Q-switched envelope, mode-locked pulses with the repetition rate of 40 MHz can be obviously seen and their repetition rate is equal to the RF driving frequency of the AOM. In our experimental observation, the width and the asymmetry ratio of the Q-switched envelopes depend on the modulation frequency of AOM. At lower modulation frequencies, satellite pulses can be seen with their number being also related to the modulation frequency of AOM. By alternation the optical focus spot size on the AO crystal, we demonstrate that the amplitude modulation of the AOM plays the dominant role for starting the harmonic mode-locking of the laser.