热重生光纤光栅模型研究

Thermal Regenerated Fiber Bragg Grating (RFBG) is a type of fiber Bragg gratings sustained ultra-high temperature. At present, the research on the modelling of RFBG is only focused on its formation mechanism. The aim of this project is to build up a modelling of RFBG. On the top of that, the research of stress change modelling on the stress relaxation during the fabrication of RFBG is using the principle of stress relaxation from the thermal annealing of the optical fiber and optical fiber internal stress profiler. Based on the stress-optic effect of the optical fiber, we are using a “FBG period measurement technique” which first reported by our group, to investigate the contraction of the period and the increase of refractive index ac component resulting from the stress relaxation of the RFBG. The refractive index dc component of the RFBG fiber core is measured by a prism coupler. The formation mechanism of the RFBG is build up based on the change of the RFBG glass network which is detected by XRD etc. The project also focuses on the research on the relation of modelling and characteristics of the RFBG, such as thermal regeneration ratio, mechanical elasticity, and sustained the ultra-high temperature technique. Finally, based on these investigations a RFBG temperature sensor should be fabricated which may have the temperature sensitivity of 15 pm/ºC at temperature measurement range of -20ºC – 1400 ºC, thermal regeneration ratio more than 10% and mechanical elasticity more than 30 MPa. The buildup of a systemic and whole modelling of RFBG can be provided the technique support for the research of fundamental theory on the fabrication of the key optical fiber based ultra-high temperature sensing element in our country.

热重生光纤光栅(thermal regenerated grating)是研究光纤光栅耐超高温技术的关键种类之一。目前国内外对其模型研究只涉及其形成机理。本项目针对热重生光纤光栅模型研究现状的不完整，利用光纤退火应力变化原理和光纤应力测量仪研究其制作过程中应力变化；利用项目组国际上首次提出的“光纤光栅周期测量技术”研究其应力减小导致的周期减小和折射率直流分量增大的物理规律，用棱镜耦合器等测量其纤芯折射率交流分量变化，建立其应力变化模型。用X射线衍射仪(XRD)等研究其纤芯玻璃成分变化，建立其形成机理模型。研究模型和热重生光纤光栅相关表征特性的关系包括热重生比率、机械弹性和耐超高温技术。在此基础上试制同时满足：温度灵敏度15pm/ºC, 测量范围-20ºC-1400ºC，热重生比率大于10%,和机械弹性大于10MPa的热重生光纤光栅温度传感器。建立系统完整的热重生光纤光栅模型，为我国超高温光

在炼油厂、高压聚乙烯制备、煤炭汽化炉、沸腾锅炉等高温环境中，对其温度进行实时监测是非常重要的，而普通的电类传感器很难适应这种超高温环境。普通的光纤布拉格光栅，随着温度升高，其折射率的周期性调制会逐渐消失。因此这类光栅也不能在大于350℃的高温环境中长时间保持，限制了光纤光栅进一步在高温环境中的应用前景。而耐高温的热重生光纤光栅（thermal regenerated grating）是这类温度监控的理想元件，特别是应用于1000℃以上高温的测量。满足光谱特性好（3dB带宽小，边模抑制比大）、高温光谱稳定度好、与普通单模光纤容易匹配等特点是耐高温光纤光栅研究领域里一系列亟待解决的技术难题。因此研究和探索具有上述优点的新型耐超高温光纤光栅十分必要。项目执行期间，重点开展三个方面的研究工作。首先对热重生光纤光栅应力变化模型进行了研究，其次对热重生光纤光栅玻璃成分变化模型进行研究，最后对所建立的模型和热重生光纤光栅相关表征特性进行了研究。研究成果1：构建了热重生光纤光栅理论模型，为后续深入研究物理模型和热重生光纤光栅相关表征特性关系包括热重生比率、机械弹性和耐温温度等铺平道路。研究成果2：实现了耐高温1400℃热重生光纤光栅的制备技术，实现了基于玻璃光纤最高温度的检测，为后续继续提高检测温度打下坚实基础。研究成果3：提出了一种基于CO2激光器的模拟“激冷激热”环境的实验技术。研究成果4：实现了超高重生比率的热重生光纤光栅专用光纤的制备技术，使用该技术制备的热重生光纤光栅的热重生比率相对于标准SM-28提高了2倍多，为解决长期困扰热重生光纤光栅的低重生比率问题提供了有效的研究思路。研究成果5：实现了基于光纤传感技术的超高温1000℃应变检测技术，以热重生光纤光栅为基础，结合封装技术，成功实现了超高温1000℃环境下的应变检测。该传感器可实现室温到1000℃范围内对应变的精确测量，在1000℃高温时，应变检测范围达1000µɛ，且精度达到1µɛ。

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