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基于多模光纤光栅光谱中拐点的温度传感研究
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Abstract:
在高温传感应用中，蓝宝石光纤光栅能够稳定传递温度变化信息，因此备受关注和青睐。但是，蓝宝石光纤光栅是多模光纤光栅，其谱线较为杂乱，当监测其反射光谱中反射峰实现传感时，存在识别困难和反射率低等问题，不利于温度传感应用中的有效识别和高精度探测。本文以多模光纤光栅为研究对象，提出了一种监测多模光纤光栅光谱中拐点实现传感的新方案。从耦合模式理论出发，研究了多模光纤光栅的耦合系数随模式阶数和圆形改性区域半径的变化规律，发现了耦合系数的拐点，并解释了其出现的原因，发现该拐点只与光纤结构有关，而与光栅的结构无关，通过追踪多模光纤光栅光谱中的拐点实现了温度传感，传感灵敏度为0.0137 nm/℃。在本文提出的传感探测方案中，光谱中拐点的识别度高，有利于高精度温度传感，为多模光纤光栅温度传感提供了新的探测方案，有望为光纤光栅的传感应用提供一个有力候选。
In high-temperature sensing applications, sapphire fiber Bragg gratings have the ability to stably transmit temperature variation information, and thus have received significant attention and favor. However, the sapphire fiber Bragg gratings are multimode fiber grating, and its spectrum is relatively disorderly. When monitoring the reflected peaks in the reflection spectrum for sensing, there are issues of difficult identification and low reflectivity, which is disadvantageous for effective recognition and high-precision detection in temperature sensing applications. This paper takes multimode fiber gratings as the research object and proposes a new scheme for sensing by monitoring the turning point in the spectrum of the multimode fiber grating. Starting from coupled mode theory, the variations of the coupling coefficients with the mode order and the radius of the cylindrical modified region are studied, and the turning point of the coupling coefficient is discovered and its occurrence is explained. It is found that this turning point is only related to the fiber structure and independent of the grating structure. Temperature sensing is realized by tracking the turning point in the spectrum of the multimode fiber grating, with a sensitivity of 0.0137 nm/？C. In the sensing detection scheme proposed in this paper, the turning point in the spectrum has high identifiability, which is conducive to high-precision temperature sensing. This provides a new detection scheme for temperature sensing based on multimode fiber gratings and is expected to offer a promising candidate for fiber grating sensing applications.
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