本文選題：飛秒激光 + 相位掩模板��； 參考：《西北大學(xué)》2017年碩士論文

【摘要】：在石油測井領(lǐng)域,如何安全可靠的獲取井中和井筒環(huán)境參數(shù),對提高油氣資源勘探和開發(fā)效率具有重要意義。光纖光柵傳感器由于自身具有一些特殊的優(yōu)點(diǎn),能夠承受井下極端的條件,因此,在光纖測井領(lǐng)域具有廣泛的應(yīng)用前景。本論文主要基于飛秒激光相位掩模板技術(shù),在三種不同類型的光纖上寫制了光纖布拉格光柵(Fiber Bragg Grating,FBG),并對其溫度、高溫應(yīng)變、彎曲三種傳感特性分別進(jìn)行了實(shí)驗(yàn)研究。利用近紅外飛秒激光結(jié)合相位掩模板技術(shù),通過改變激光光斑的聚焦位置,在單模光敏光纖上刻寫了三種不同類型的FBG,柵區(qū)覆蓋光纖纖芯和部分包層區(qū)域,光柵透射光譜圖呈現(xiàn)出兩個(gè)分立的共振模式,分別為纖芯模式和包層模式。其中,我們選擇包層折射率調(diào)制大于纖芯折射率調(diào)制的FBG進(jìn)行溫度測試實(shí)驗(yàn)。結(jié)果表明,包層FBG和纖芯FBG 一樣具有很好的耐溫性,且其溫度響應(yīng)靈敏度與纖芯FBG的幾乎相等,因此也可用于高溫場所溫度變化量的監(jiān)測。利用飛秒激光側(cè)面照射技術(shù),在經(jīng)過載氫處理的多模光纖上刻寫了三種不同類型的FBG。將激光聚焦在多模光纖纖芯的不同位置,會激發(fā)不同的光纖模式。當(dāng)光斑位于纖芯中心軸時(shí),僅纖芯基模被激發(fā);移動(dòng)光斑,使聚焦光斑偏離纖芯軸約10μm,多個(gè)高階模式和纖芯基模同時(shí)被激發(fā);繼續(xù)移動(dòng)光斑,當(dāng)光斑偏離纖芯軸約20μm時(shí),只有多個(gè)高階模式被激發(fā)。僅有纖芯基模的FBG被用來進(jìn)行高溫應(yīng)變測試實(shí)驗(yàn)。結(jié)果表明,溫度越高,傳感器應(yīng)變靈敏度越高,最高可達(dá)5.24pm/με。因此,多模光纖布拉格光柵尤其適用于高溫場所應(yīng)變的監(jiān)測。利用飛秒激光結(jié)合相位掩模板技術(shù),通過將激光光斑聚焦在經(jīng)過載氫處理的光纖纖芯與第一包層的界面處,在一種具有折射率下陷第一包層的四包層單模光纖上寫制了 FBG,光柵結(jié)構(gòu)覆蓋光纖纖芯和部分第一包層區(qū)域。并且通過實(shí)驗(yàn)研究了光柵的彎曲和溫度特性。彎曲試驗(yàn)結(jié)果表明,反射的包層FBG的強(qiáng)度對光纖微彎響應(yīng)靈敏,且由于包層FBG在光纖橫截面的不對稱分布,彎曲響應(yīng)具有很高的方向依賴性。但是,包層共振波長對彎曲不敏感,因此可以通過分別監(jiān)測包層反射峰的能量和波長信息,來實(shí)現(xiàn)彎曲和溫度的同時(shí)區(qū)分測量。多包層FBG的成功研制,對于結(jié)構(gòu)健康的監(jiān)測具有重大意義。
[Abstract]:In the field of petroleum logging, how to obtain the environmental parameters of well neutralization and wellbore safely and reliably is of great significance to improve the efficiency of exploration and development of oil and gas resources. Fiber Bragg grating (FBG) sensors can withstand extreme downhole conditions because of their own special advantages. Therefore, FBG sensors have a wide application prospect in the field of optical fiber logging. Based on femtosecond laser phase mask technique, fiber Bragg grating (FBG) is fabricated on three different types of fiber in this paper. The temperature, high temperature strain and bending characteristics of fiber Bragg grating (FBG) are studied experimentally. Using near infrared femtosecond laser combined with phase mask technique, three different types of FBGs were written on single mode Guang Min fiber by changing the focusing position of laser spot. The gate region covers the fiber core and part of the cladding region. The transmission spectra of the grating show two discrete resonance modes, one is the core mode and the other is the cladding mode. Among them, FBG with cladding refractive index modulation larger than core refractive index modulation is selected for temperature measurement. The results show that the cladding FBG has good temperature resistance as fiber core FBG, and its temperature response sensitivity is almost equal to that of core FBG, so it can also be used to monitor the temperature change in high temperature sites. Using femtosecond laser side-irradiation technique, three different types of FBGs have been written on the hydrogen-carrying multimode fiber. Focusing the laser in different positions of multimode fiber core excites different fiber modes. When the spot is located in the central axis of the core, only the core mode is excited; when the spot is moved, the focusing spot deviates from the core axis about 10 渭 m, and several higher-order modes and the core base mode are excited simultaneously; and the light spot continues to move, when the spot deviates from the core axis about 20 渭 m, Only multiple higher order models are excited. Only FBG with core-based mode is used for high-temperature strain test. The results show that the higher the temperature, the higher the strain sensitivity and the maximum 5.24pm/ 渭 蔚. Therefore, multimode fiber Bragg grating is especially suitable for strain monitoring at high temperature. By using femtosecond laser combined with phase mask technology, the laser spot is focused on the interface between the fiber core and the first cladding after hydrogen transfer. FBGs are written on a four-cladding single-mode fiber with a first cladding of refractive index. The grating structure covers the fiber core and part of the first cladding region. The bending and temperature characteristics of the grating are studied experimentally. The bending test results show that the strength of the reflected cladding FBG is sensitive to the micro-bending response of the fiber, and the bending response is highly directionally dependent due to the asymmetric distribution of the cladding FBG in the fiber cross section. However, the cladding resonant wavelength is not sensitive to bending, so it is possible to measure the bending and temperature simultaneously by monitoring the energy and wavelength information of the reflected peak of the cladding. The successful development of multi-cladding FBG is of great significance for structural health monitoring.
【學(xué)位授予單位】：西北大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2017
【分類號】：TN253

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