主動電光調變鎖模半導體增益光纖雷射之研究

Abstract

本論文主要使用電光相位調變作為主動鎖模機制，以半導體光放大器作為增益介質，使用Lyot filter作為光濾波元件，實際製作出重複率為10 GHz、輸出功率為 2 mW、脈衝寬度為 18 ps的鎖模半導體光放大器光纖雷射。在實驗上藉由控制極化和幫補電流大小，可將雷射之單波長鎖模狀態轉變成雙波長鎖模狀態。在單波長鎖模態方面，我們使用色散補償光纖作線性脈衝壓縮，可將原先輸出的脈衝寬度壓到10 ps以下。在雙波長鎖模態方面，我們將脈衝序列傳遞在色散光纖中，利用兩波長在傳遞上的時間差準確計算出光纖的色散值，所得計算值與實際值相當吻合，應可用來量測未知光纖的色散。 我們也將主動鎖模機制由相位調變換成強度調變，在重複率為10 GHz 的情況下改變不同幫補電流大小和調變強度來記錄光譜頻寬(bandwidth)、脈衝寬度(pulse width)、時間-頻寬乘積(time-bandwidth product)和超模抑制比(super-mode suppression ratio) 等特性，嘗試比較相同架構下相位調變和強度調變鎖模的差異

In this thesis study we mainly utilize EO phase modulation as the active mode-locking mechanism to build a mode-locked fiber laser. The semiconductor optical amplifier (SOA) is used as the gain medium and a fiber-type Lyot filter is inserted inside the laser cavity for optical filtering. The mode-locked SOA fiber laser can be operated at the single wavelength mode-locking state as well as the dual wavelength mode-locking state. Under single wavelength mode-locking, the laser can generate a 10 GHz pulse train with the average power of 2 mW and pulse width of 18 ps. The pulse width can be reduced below 10 ps by using a section of dispersion compensating fiber for external compression. Under dual wavelength mode-locking, if we let the output pulses propagate through a dispersive fiber, the fiber dispersion can be accurately calculated from the time delay change of the two pulses after a known propagating length. The calculated value is in excellent agreement with the known specification of the fiber. We have also replaced the phase modulation with the amplitude modulation for comparison. Under different pump currents and modulation intensities, the bandwidth, pulse width, time-bandwidth product and super-mode suppression ratio of the lasers are recorded. The results under the two modulation mechanisms in the same laser structure at the repetition rate of 10 GHz are carefully compared.