Abstract
光纖用途廣大；主要應用於光通訊及各種物理量感測器方面;其優點為体小質輕、高靈敏度、不受電磁干擾、保密性佳...等等，在感測器方面,幾乎所有傳統感測氣所能量測到的物理量,都可用光纖感測器來量,又其有以上所說優點,故其用途日廣，亦愈形重要。早先利用兩根鍍金光纖Mach-Zehnderinterferometer型式之光纖電流感測器，提供了線性量測關係及高靈敏度之特性，但其頻寬非常低落，此因其干涉後之相位變化為與頻率成反比的關係。進一步的改善頻寬方法為先把待測電流訊號做微分 (即pre-differentiation technique)，再流經感測分流電路,這種方法可把量測頻寬擴展到1.1kHz(以用80微米之光纖而言)，雖用較細之光纖可更提高頻寬，但終究有限,畢竟光纖總不能異常細。為了更進一步提高此光纖電流感測器的頻寬，於是本論文提出一些改進的方法，改以固定頻差量測方式來達成,亦即不在直接量測待測電流訊號頻率成份,而是將 biascurrent Ib以交流訊號來做,則光檢測器檢測出的相位變化就有倍頻,合頻,差頻成份,今我們只萃取差頻成份,則一旦待測電流頻率改變,讓biascurrent Ib 頻率隨之變化,且兩者的頻差永遠固定,則預期,頻率響應頻寬將不在隨頻率增加而變化.因為我們取的訊號已是變為固定頻率.由實驗結果看來，本文所提出之方法，確實大大的提高量測頻寬，且有著線性、高靈敏度及高穩定度的特性。此外，於實驗中所遭遇的問題，亦提出一些解決方法。更進一步促進其實用性。This thesis is focused on the study of fiber-optic electriccurrent sensors. The electric current measurement schemeemploying two metal-coated single mode optical fibers assensing elements two metal-coated single mode optical fibers assensing elements is reviewed in the first part. The pre-differentiation technique used to widen the measurementbandwidth is outlined here. In the second part of this thesis,a method of further improving the band performance of electriccurrent measurement is described and put into test.Experimentsshow that a very large measurement bandwidth canqbe obtained byuse of this proposed method in which only an offset frequencycomponent is detected for whatever the measurand frequency is.In the test experiments, we have shown quite a flatcharacteristics in frequency response up to 20 kHz.