本實驗為一分布式光纖入侵感測定位系統，使用一自製窄線寬雷射光源等比例分成兩道光從正向及逆向打入一用來偵測入侵之馬赫詹德干涉儀，並在人為敲擊感測光纜後，利用接收到之干涉訊號判定入侵位置。本實驗計算振動引起的訊號之三個參數值，判斷其是否超出閾值以決定光纜是否受到入侵振動，並利用傅立葉轉換搭配特徵閾值來決定入侵位置，並利用一秒內多圖平均之方式來減少誤差過大之情況。

In this study, we use a self-made narrow linewidth fiber laser as a light source for the optical intrusion detection system. We split the laser light into two parts by a 5:5 fiber coupler and launch them into the same Mach-Zehnder interferometer at the two ends, respectively, such that one input laser light goes clockwise and the other one goes counterclockwise. Swatting the fiber cable, we measure the interference patterns collected by a DAQ card and use them to position the location of swatting. Such swatting may correspond to intrusion that is to be detected and located. The swatting effectively caused a vibration upon the fiber cable that contained a Mach-Zehnder interferometer for detecting the intrusion. We use 3 thresholds to define whether the fiber cable is being intrusively vibrated or not. Besides, we use Fourier transform method to locate the intrusion. Finally, we average the positions calculated for multiple time frames that sum up to one second to improve the location accuracy.

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