本論文利用實驗室自製馬克詹德干涉儀搭配環形共振腔產生的脈衝打進八點八公里的長光纖，來測量背向雷利散射。由於馬克詹德干涉儀會因為光纖震動所產失的相位變化發生建設性干涉或破壞性干涉，就可以利用此機制來產生脈衝。當產生破壞性干涉時，共振腔裡無能量產生。當為建設性干涉時，共振腔裡有極高的能量，就會形成脈衝。而我們將此脈衝打入感測光纖裡，來產生背向的雷利散射。雷利散射也會因為光纖的震動或是拍擊所產生的相位變化而有能量強度的高低變化。利用此散射的強度變化，我們可以來推測出光纖中的扭曲抑或是經由入侵引起之相位變化造成的干涉，即可反推出入侵訊號在光纖中的位置，以此來達到防區的效果。

In this paper, we use a pulse laser, formed by incorporating a Mach-Zehnder interferometer in a ring resonator of a fiber laser, and launch the pulse into an 8.8 kilometer bare fiber, to detect backward Rayleigh scattering. The Mach-Zehnder interferometer is very sensitive to the phase difference caused by the perturbation on the fiber. So when it is destructive interference, it means there is no power in the cavity. On the contrary, there will be lots of energy when constructive interference occurs. Backward Rayleigh scattering is also sensitive to the phase difference caused by the perturbation on the fiber. So it means that when there is a phase difference caused by the perturbation on the fiber, the power of backward Rayleigh scattering would change. We can then determine whether the fiber is bent or vibrated by inspecting the power variation of the backward Rayleigh scattering. So this system can be used for security of perimeter zones.

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