【摘要】：基于相位敏感型光時(shí)域反射(φ-OTDR)原理的分布式光纖振動(dòng)傳感系統(tǒng)利用光纖中背向瑞利散射光受振動(dòng)信號(hào)調(diào)制的原理對(duì)光纖沿線的振動(dòng)信號(hào)進(jìn)行探測(cè)。由于光纖本身既是傳輸介質(zhì)也是φ-OTDR系統(tǒng)的傳感介質(zhì),因此它可以實(shí)現(xiàn)長(zhǎng)距離分布式的振動(dòng)傳感,這在長(zhǎng)距離軌道安全監(jiān)測(cè)、長(zhǎng)距離管道安全監(jiān)測(cè)方面具有無(wú)可比擬的優(yōu)勢(shì)和廣泛的應(yīng)用前景。目前φ-OTDR系統(tǒng)的研究方向主要集中于對(duì)背向瑞利散射光的數(shù)字信號(hào)采集和相位信息解調(diào)與處理的算法研究,但實(shí)時(shí)數(shù)字信號(hào)的采集和處理需要高性能的采集板卡和計(jì)算設(shè)備。因此本文提出了一種基于模擬外差鑒相電路對(duì)φ-OTDR系統(tǒng)的背向瑞利散射光的相位信息進(jìn)行解調(diào)的方法,其主要的工作內(nèi)容和創(chuàng)新點(diǎn)集中在以下幾點(diǎn):首先,根據(jù)φ-OTDR理論結(jié)構(gòu)搭建了模擬外差解調(diào)型φ-OTDR系統(tǒng)。在搭建過(guò)程中,主要對(duì)數(shù)據(jù)采集、光脈沖調(diào)制、耦合器分光比等一些系統(tǒng)參數(shù)進(jìn)行了設(shè)計(jì),使其達(dá)到各項(xiàng)探測(cè)性能的要求。隨后對(duì)φ-OTDR系統(tǒng)中光功率和光源線寬對(duì)系統(tǒng)性能的影響進(jìn)行了分析和驗(yàn)證,經(jīng)過(guò)功率優(yōu)化找到最佳的脈沖探測(cè)光功率,優(yōu)化了系統(tǒng)的信噪比。在模擬外差鑒相部分,在AD8302模擬鑒相芯片的基礎(chǔ)鑒相功能之上設(shè)計(jì)了雙路AD8302參考鑒相電路,并進(jìn)行了PCB板的設(shè)計(jì)與制作。經(jīng)過(guò)實(shí)測(cè),將鑒相范圍由0°到180°擴(kuò)展到了0°到360°,并且通過(guò)鑒相解調(diào)程序?qū)﹁b相特征曲線的非線性區(qū)域進(jìn)行修正,大大的降低了AD8302的鑒相誤差,鑒相特征曲線的鑒相最大誤差由7°左右下降至1.1795°。隨后,將鑒相電路模塊加入了φ-OTDR系統(tǒng)進(jìn)行了外差解調(diào)實(shí)驗(yàn),并成功實(shí)現(xiàn)了對(duì)5.09km處的振源進(jìn)行定位。通過(guò)模擬外差解調(diào)與數(shù)字外差解調(diào)方案的比較,模擬外差解調(diào)的解調(diào)精度低于數(shù)字外差解調(diào)的精度,這主要是因?yàn)橥獠钚挺?OTDR系統(tǒng)的混頻信號(hào)具有一定的邊頻帶,且信號(hào)幅值受偏振衰落和相位衰落等因素的影響,其解調(diào)幅值存在一定的波動(dòng),這兩種因素導(dǎo)致了AD8302模擬鑒相電路出現(xiàn)較大的誤差。但是應(yīng)當(dāng)看到的是,通過(guò)模擬鑒相實(shí)現(xiàn)了對(duì)混頻信號(hào)的模擬下變頻處理,使得數(shù)據(jù)采樣率由數(shù)字外差解調(diào)方案的1GSa/s降低到了模擬外差解調(diào)方案的10MSa/s,可以極大的降低外差式φ-OTDR系統(tǒng)的成本。最后,針對(duì)上述問(wèn)題提出將AOM反饋控制和模擬方波鑒相技術(shù)引入φ-OTDR系統(tǒng),以提高模擬鑒相的精度。
[Abstract]:A distributed optical fiber vibration sensing system based on phase-sensitive optical time domain reflection (蠁 -OTDR) detects the vibration signals along the fiber by using the principle that the Rayleigh backscattering light in the optical fiber is modulated by the vibration signal. Since optical fiber itself is both a transmission medium and a sensing medium for 蠁 -OTDR system, it can realize long distance distributed vibration sensing, which can be monitored safely in long distance orbit. Long-distance pipeline safety monitoring has unparalleled advantages and wide application prospects. At present, the research direction of 蠁 -OTDR system is mainly focused on the algorithms of digital signal acquisition and phase information demodulation and processing of backscatter light. However, the acquisition and processing of real-time digital signals require high performance acquisition boards and computing equipment. Therefore, this paper presents a demodulation method based on analogue heterodyne phase discriminant circuit to demodulate the phase information of backscattered Rayleigh light in 蠁 -OTDR system. Its main work and innovation are as follows: first, According to the 蠁 -OTDR theory structure, the simulated heterodyne demodulation 蠁 -OTDR system is built. In the process of building, some system parameters, such as data acquisition, optical pulse modulation, coupler split-light ratio and so on, are designed to meet the requirements of the detection performance. Then the influence of optical power and light source linewidth on system performance in 蠁 -OTDR system is analyzed and verified. Through power optimization, the optimal pulse detection optical power is found and the signal-to-noise ratio of the system is optimized. In the part of analogue heterodyne phase detection, the dual AD8302 reference circuit is designed based on the function of AD8302 analog phase detector, and the PCB board is designed and fabricated. The range of phase detection is extended from 0 擄to 180 擄to 0 擄to 360 擄, and the nonlinear region of the phase characteristic curve is corrected by the phase demodulation program, which greatly reduces the phase discrimination error of AD8302. The maximum error of the phase discrimination curve decreased from about 7 擄to 1.1795 擄. Then, the phase detection circuit module is added to 蠁 -OTDR system for heterodyne demodulation experiment, and the location of vibration source at 5.09km is realized successfully. Through the comparison between analog heterodyne demodulation and digital heterodyne demodulation, the demodulation accuracy of analog heterodyne demodulation is lower than that of digital heterodyne demodulation, which is mainly due to the fact that the mixing signal of heterodyne 蠁 -OTDR system has a certain side band. The amplitude of the signal is affected by polarization fading and phase fading, and the demodulation amplitude fluctuates to a certain extent. These two factors lead to large errors in the AD8302 analog phase discriminator circuit. However, it should be noted that the analog downconversion processing of mixing signals is realized through analog phase discrimination. The data sampling rate is reduced from the digital heterodyne demodulation scheme (1GSa/s) to the analog heterodyne demodulation scheme (10msa-s), which can greatly reduce the cost of the heterodyne 蠁 -OTDR system. Finally, AOM feedback control and simulated square wave phase detection technique are introduced into 蠁 -OTDR system to improve the accuracy of simulation phase detection.
【學(xué)位授予單位】：電子科技大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類號(hào)】：TP212;TN253

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本文編號(hào)：2206773