我們提出利用摻鉺光纖放大器(Erbium Doped Fiber Amplifier, EDFA)透過泵激光源(pumping source) 的調變會間接使放大自發輻射帶有調變信號的特性，調變後之放大自發輻射(amplified spontaneous emission, ASE)當做為監控信號光源來即時、線上及不中斷的量測極化模態色散(polarization mode dispersion, PMD)之技術，在一個由多個摻鉺光纖放大器(EDFA)所組成分波多工(dense wavelength division multiplexed, DWDM)光通訊系統，利用我們提出的技術具有不必另外增加光源、不佔用既有的信號及不受極化相關損失(polarization dependent loss, PDL)等優點，而這個技術是使用頻率領域(frequency doamin)的方法卻擁有時間領域(time domain)方法的即時量測的優點並避免了時間領域方法實際安裝不易的缺點。為提高解析度，我們也提出串聯多個可調式聲光濾波器(acousto-optics tunable filter, AOTF)來量測極化模態色散(PMD)的值。當光在此非等向 (anisotropic) 可調式聲光濾波器中傳輸時，由於不同的極化方向及聲光效應的影響，對光的折射率也會不同，本文中一併討論可調式聲光濾波器的極化模態色散，依此理論可調聲音大小來控制聲光濾波器的群速延遲差(differential group delay, DGD)。最後我們可藉由理論及實驗，來驗證理論模型的正確性。

We propose an on-line, wide-band, adaptive, and no data traffic interruption polarization mode dispersion (PMD) monitoring system based on the modulated amplified spontaneous emission (ASE) and cascaded acousto-optics tunable filters (AOTFs) techniques. This method is applicable to a long-haul, multiple erbium-doped fiber amplifiers (EDFAs), dense wavelength division multiplexing (DWDM) optical transmission system. Due to the unique properties of the non payload signal bearing and wide-band existence, the ASE noise of one of the EFDAs is employed as the supervisory (SV) signal and becomes traceable during transmission by modulating it with low-frequency rf signal. In addition, the AOTFs are used seriously at the receiver side due to its prominently refractive-index adjustability and wide channel scanning properties. This method is based on frequency domain measurement, which has many advantages for implementation.
Using the fixed-analyzer method, PMDs of different wavelength bands which range from 1545-1580nm of an DWDM optic-fiber communication system can be found by adaptively changing the radio frequency of the AOTF. The resolution of the proposed monitoring system can be improved by cascading the AOTFs at the receiver side.
To prove the validity of our method, the theoretical results are compared with the experimental data. A high degree of agreement is observed.

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