光纖被動網路已經被視為是下一代的接取網路解決方案，但是由於光纖被動網路採用的是樹枝狀架構，因此傳統用於斷線分析的光時域分析儀並不適用在這個架構上。雖然已經有人提出以光纖光柵搭配波長可調式光源的解決方案，但是這個方案並不符合成本效益，並且無法導入大量生產。因此本論文主要在設計低成本的新型光網路監控系統，此監控方式適用在樹枝狀結構的分時多工被動網路，我們在中央機房發送一個波長調變光源，而用來監控之特殊反射式干涉元件則放置在用戶端，由機房端發送的波長調變光源透過光纖網路傳遞並在用戶端經過干涉後，元件會產生特定頻率的時域訊號，此訊號接著反射回中央機房，由於各用戶端的干涉元件所產生的訊號週期不同，因此所有干涉訊號可以透過簡單的計算反射訊號在頻譜上的強弱來判斷中央機房到用戶端的光纖網路是否出現狀況。
此架構使用的干涉元件具有容易大量製造以及積體化的優點，非常容易和現存的元件整合在一起。在本論文中將討論此種監控方式相較於光時域反射儀以及光頻域反射儀的優缺點，以及在用戶端使用的干涉元件，在採用不同類型干涉元件下的效果比較，並且討論此種監控方式使用在樹狀結構的分時多工系統下，接收器需要的靈敏度，以及合適的電路設計方式。

Passive optical networks (PONs) are becoming the popular solutions for access networks due to the advantages of low cost, large capacity, and easy maintenance. For enhancing the survivability, the PON system must have fault detection capability. Because a PON system has a point-to-multipoint topology, the backscattered signals from the distribution fibers overlap together, making the fault detection difficult by using the conventional optical time domain reflectometer (OTDR). To monitor the failure of distribution fibers, a tunable light source at the central office (CO) and a fiber Bragg grating (FBG) at each optical network unit (ONU) was demonstrated. However, this monitoring system is not cost-effective because of the use of OSA, and FBGs. The FBG is difficult to be mass produced or integrated with other active and passive components in order to further reduce the cost of ONUs.
Therefore, we propose a new monitoring scheme that employs a continuous wavelength sweeper at the CO and an interferometric (IF) device at each ONU. The CO send a frequency-modulation signal and then the IF devices reflect the interference signal to the CO. The reflected signal from each ONU can easily be distinguished from the others by performing a Fourier transform. The corresponding spectral component will disappear if one of the distribution fiber is broken. This scheme provides versatility for fault monitoring by using low-cost and mass-producible components. We will discuss the performance by using different IF device at ONUs. The effect of sweeper light source, the design of the receiver circuit, and the sensitivity and linearity of this monitoring system will be investigated in detailed. Also, we discuss the advantages and drawbacks between the proposed monitoring scheme and the OTDR and optical frequency domain reflectometer (OFDR) schemes.

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