隨著寬頻應用時代的來臨，使用者的頻寬需求越來越大。光纖網路已成為目前寬頻有線網路的最佳方案。在接取網路技術中，以被動光網路(Passive Optical Network, PON)最具優勢。它能提供高品質與超寬頻的傳輸網路服務，但是只需要一些被動光元件放置在局端與用戶端之間。因此可避免主動元件暴露於室外環境中所衍生的施工及維護問題。故被動光網路架構可以同時符合簡化網路設計、降低佈建及維修成本等要求。為了確保網路服務的品質，如何有效地維護被動光網路系統實為非常重要的課題。 在本篇論文中，我們提出一故障監測系統，在被動光網路中可偵測出分佈光纖(Distribution Fiber)的斷裂及光網路單元(Optical Network Unit, ONU)的狀態。此故障監測系統採用輪詢(Polling)模式運作。在ONU端的光監測單元(Optical Monitoring Unit, OMU)以一顆法布里-珀羅(Fabry-Perot, FP)雷射二極體作為光收發機(Transceiver)，平常操作在接收狀態；當OMU接收到它的識別頻率時，FP雷射二極體將轉變為發射狀態，並依據ONU的狀態然後調變上一相對應的音頻音。在此情況下，光線路終端(Optical Line Terminal)的音解碼器(Tone Decoder)可解碼出每一分佈光纖及ONU的狀態。 With the upcoming era of broadband applications, the users are going to demand far more bandwidth. Fiber-optic network has become the best solution in wired broadband networks. Among the existing access network technologies, passive optical network (PON) is predominant. It can provide high quality and ultra-wideband transmission network services, but it only needs some passive optical components placed in the region between the central office and end users. Thus construction and maintenance issues derived from the exposure of active optical components in the outdoor environment can be avoided. Therefore, passive optical network architecture can simultaneously meet the requirements for simplifying network design and reducing the cost of deployment and maintenance. In order to ensure the quality of network service, how to effectively maintain the passive optical network system is indeed very important as an issue. In this thesis, we propose a fault monitoring system, which can detect the breaking of distribution fibers and monitor the statuses of optical network units (ONUs) in passive optical networks. This fault monitoring system adopts the operation in polling mode. An optical monitoring unit (OMU) at an ONU, which employs a Fabry-Perot (FP) laser diode as an optical transceiver, normally operates in receiving state. When an OMU receives its identity frequency, FP laser diode will be turned into transmitting state and then be modulated by a corresponding tone according to the status of an ONU. Under the circumstances, the tone decoder at the optical line terminal can decode the statuses of each distribution fiber and ONU.
