多泵浦光源應用於拉曼放大器中之特性研究

Abstract

本篇論文中，是利用三個不同波長(14xx nm)的泵浦雷射作為光源，以三種不同的光纖作為增益介質，去量測各種光纖的拉曼增益值。我們嘗試調整各波道泵浦光的輸出功率，使得拉曼增益曲線能趨近平坦、並有最大的增益頻寬。在50km的單模光纖中，我們得到5.33dB的峰值增益，平坦度1dB的頻寬達35nm。在50km的非零色散光纖中，我們得到5.22dB的峰值增益，平坦度1dB的頻寬達40nm。在15.4km的色散補償光纖中，得到7.84dB的峰值增益，平坦度1dB頻寬達36nm。 其次，我們由實驗求得在雙向泵浦放大架構中，前向與背向泵浦功率的最佳比例。當此比例為9:91時，可得到最佳的拉曼增益及噪聲指數。 最後，我們提出實驗中觀察到的四波混頻現象。此現象發生在前向泵浦放大架構並以非零色散光纖作為增益介質時。其原因在於泵浦光與特定波長信號光的群折射率(ng)幾乎相等、造成相位一致，進而發生泵浦光的多模頻譜在信號光處產生的四波混頻現象。因此我們建議若欲以非零色散光纖作為拉曼放大器的增益介質時，最好採取背向背大的架構；若欲使用前向放大的架構，則需慎選泵浦光源的波長>1460nm，來放大L-band的訊號，如此方可避免產生在非零色散光纖中的四波混頻現象。

In this thesis, we use three different wavelength 14xx LDs as pumping source to measure the Raman gain of three different fibers：SMF、LEAF and DCF. We try to adjust each pump power to make gain flatten then get a wide flatten bandwidth. 1dB flatness Raman gain over 35nm bandwidth can be achieved in 50km SMF with peak gain 5.33dB while 40nm bandwidth can be achieved in 50km LEAF with peak gain 5.22dB. 1dB flatness Raman gain over 3nm bandwidth can be achieved in 15.4km DCF with peak gain 7.84dB. Then we want to find out the best ratio of forward and backward pump power in bi-directional pumping Raman amplifier. Result has that 9:91 is the ideal ratio when bi-directional pumping is applied in Raman amplifier. In the case of using LEAF as the gain medium, forward pumping will cause FWM between pump and signal. We suggest backward pumping or choosing longer pump wavelength (>1460nm) in forward pumping to amplify L-band WDM signals in order to avoid FWM in LEAF.