利用RF頻譜量測搭配波長掃描調變光源來量測群速度色散之研究

Abstract

在此光纖通訊日益普遍和被廣泛應用的時代，如何在長距離的光纖傳輸中保持訊號不失真是一個重要的課題。因為傳輸光纖本身的群速度色散能影響頻寬和可傳輸的距離，所以群速度色散的經濟有效量測方法一直也是研究開發上的重點。本論文針對此需求提出一個非干涉式光纖群速度色散量測方法，僅需RF頻譜分析儀而不需更昂貴之網路分析儀。我們首先利用振幅調變器被加載弦波訊號來調變寬頻光源的輸出光並透過可調光濾波器來進而得到一個波長掃描式的調變光源，此光源具有10GHz高調變頻率，其中心波長呈慢速的周期性變化。然後藉由RF頻譜分析儀觀察此光源的輸出光經過待測光纖前後的RF頻譜差異，透過進一步地理論分析可以成功得出待測光纖之群速度色散值，所得結果與已知的光纖規格有很好的吻合。

Fiber communication has played a major role in the information age nowadays due to the vast advantages of optical fibers over existing copper wires. Since the transmission distance or bandwidth is impacted by the fiber dispersion, the measurement of fiber dispersion has been an important R&D focus. In the thesis, an economic non-interferometric method is developed to measure the group velocity dispersion of optical fibers. A modulated wavelength-swept light source is created with a broadband source followed by an EO modulator and a tunable optical filter. The source is intensity-modulated at the 10GHz high frequency with a slow periodic central wavelength variation. By measuring the RF spectra before and after the light propagates through the test fiber, the group velocity dispersion coefficient of the test fiber can be experimentally determined through the developed theory.