光分碼多重擷取技術應用於全光纖環狀振動感測器

Optical Code Division Multiple Access Application in All Fiber Loop Vibration Sensor

許榮順(Rong-Shun Syu)

指導教授 ： 鄭旭志

國立虎尾科技大學/電機資訊學院/光電與材料科技研究所/碩士(2011年)

https://doi.org/10.6827/NFU.2011.00134

摘要

本論文提出一個使用頻譜振幅編碼之光分碼多重擷取(Spectral Amplitude Coding Optical Code Division Multiple Access, SAC OCDMA)架構來擷取全光纖環振動感測器上的待測物振動頻率，根據每個使用者擁有各自的頻譜振幅編碼，使用多重光纖布拉格光柵(Fiber Bragg grating, FBG)陣列的FBG編碼器-解碼器，在頻域中提供良好的正交特性，也降低使用者間多重處理干擾(Multiple Access Interference, MAI)。
光纖環狀感測器，是當光纖彎曲至超過臨界半徑時，對於外在物理參教會很敏感，像是溫度、應變和振動等等。而在全光纖環狀振動感測器(All Fiber Loop Vibration Sensor, AFLVS)中，是將一段光纖繞成特定半徑的光纖環，放置於經設計過的振動平台。
首先，系統利用1×K耦合器將寬頻光源分割為K個光源，然後傳送至各個FBG編碼器，而全光纖環振動感測器被加入在各個FBG編碼器的光循環器與多重FBG陣列間，並將步進馬達直接放置於各個全光纖環振動感測器的光纖環上，以訊號產生器輸入不同頻率至各個感測器的步進馬達。FBG編碼器輸出反射光譜的光強度經由AFLVS調變後，由光循環器輸出調變過的反射訊號至K×K星狀耦合器，然後散播至各個使用者的FBG解碼器中。接下來，我們利用平衡光檢測器(Balanced Photo-detector, BPD)將FBG解碼器的光輸出傳換為電訊號，使用數位示波器將BPD輸出的電訊號做傅立葉轉換，即可得知待測物的振動頻率。而實驗結果會與壓電式加速規做比較，顯示壓電式加速規只在90Hz內的低頻較不靈敏，相對地AFLVS的在低頻50Hz-70Hz較好。
而AFLVS，有體積小、重量輕和不受電磁波干擾的特性，可實現多點或分佈式感測，這種彈性且簡單的優點被認為可以補償傳統電子或機械感測器的缺點。

關鍵字

頻譜振幅編碼 ； 光分碼多重擷取 ； 光纖彎曲 ； 光感測器 ； 振動頻率量測

並列摘要

A procedure is proposed an approach that extracts vibration frequency of measurement object using spectral amplitude coding optical code division multiple access (SAC OCDMA) with All fiber loop vibration sensor. According to each users owing spectral amplitude coding, fiber Bragg grating (FBG) encoder-decoder provides good correlation property using multiple FBG chain. It decreases multiple access interference (MAI) among users too.
Fiber loop sensor, which are sensibility to external physical quantity when optical fiber bending until exceed critical radius, including temperature, stress, vibration etc. Fiber loop are placed to designed vibration stage after bending a section of optical fiber to specify radius in fiber loop vibration sensor.
First, the system employs a 1×K optical coupler to divide broadband source light into K light to supply each FBG encoder. All Fiber loop vibration sensor located between the optical circular and multiple FBG chain at each FBG encoder, and then direct placed step motor on fiber loop of fiber loop vibration sensor. The difference frequency input to each sensors of step motor by using signal generator. The FBG encoder output the light intensity of reflected spectrum modulated by fiber loop vibration sensor. Each of optical circular sends modulated signal reflected from FBG encoder to K×K star coupler and broadcast to each user’s decoder. Next, we convert output of FBG decoder to electrical signal using balanced photo-detector (BPD). The fast Fourier transform functions of digital Oscilloscope was used for analyzing electrical signal from BPD, and then obtains vibration frequency of measurement object. Experiment results compared with piezoelectric accelerometer. The measured results show that piezoelectric accelerometer is only insensitivity at lower vibration frequency (under 90Hz). Relatively the low frequency of all fiber loop vibration sensor work well at 50-70Hz.
Fiber loop vibration sensor, which has the advantage of light weight, compact size, reject from electro-magnetic interference, and it can easy to realize multipoint or distributed sensing. This flexibility and simplicity are great advantages as regards compesensating for disadvantage of conventional electrical and mechanical sensor.

Keywords: Spectral amplitude coding, Optical code division multiple access, Fiber bending, Optical fiber sensor, Vibration frequency measurement.

並列關鍵字

Spectral amplitude coding ； Optical fiber ； Optical code division multiple access ； Fiber bending ； Optical fiber sensor ； Vibration frequency measurement

參考文獻

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