論文摘要
Double pass L-band EDFA相較於Single pass L-band EDFA有較好的PCE，並且使用較短的EDF，所以本論文討論如何設計Double pass L-band EDFA，先討論傳統的Double pass L-band EDFA的架構，發現有雜訊指數過高以及power conversion efficiency(PCE)不佳等情況，也因為如此，我們的論文會在第三章引入新的架構，使得雜訊指數降低，而第四章主要為提高PCE，做法如下，將傳統的Double pass L-band EDFA， 40m長度的EDF，分為兩段，成為25m加上15m un-pump EDF的架構，在25mEDF後置入1480 nm pump power，15m的un-pump EDF便可以吸收後向的C-band ASE，如此可以達成有效利用後向C-band ASE，25mEDF前端(也就是circulator端，port 2)置入980 nm pump power，我們利用的是980 nm pump power的低雜訊指數特性，置於EDFA前端，用來降低雜訊指數。第四章的內容如下，一般傳統Double pass L-band EDFA使用50/50 coupler來做為Fiber Loop Mirror，如此，不需要的L-band ASE會在系統中被Mirror放大兩次，因為對於不需到的光訊號進行放大，所以造成pump laser能量的浪費，所以我們使用FBG置換掉Fiber Loop Mirror，當使用FBG置換掉Fiber Loop Mirror後，L-band ASE只會被放大一次，第二次會在FBG端被濾掉，因為如此，在能量的有效利用下， 25mEDF前端的不會被第二次放大的L-band ASE搶奪population，這樣可以大大的改善power conversion efficiency(PCE)、增益、雜訊指數，如此我們可以達成高增益以及低雜訊的EDFA系統。

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