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Studies On A Scheme Of Temperature Sensitivity Enhancement Of Fiber Bragg Grating

Posted on:2008-09-18Degree:MasterType:Thesis
Country:ChinaCandidate:Z S ZhaoFull Text:PDF
GTID:2178360212496680Subject:Optics
Abstract/Summary:PDF Full Text Request
With the development of society, people have an increasing demand for information. As one of the three mainstays of modern information technology, the information collection technology (sensor technology) is becoming more and more important.Fiber Grating is a new type of passive optical components.It can change or control the behavior of optical transmission in the region. As a new technology of photon research, Fiber Bragg Grating(FBG) sensors are attracting considerable interests in research and applications.In this paper, we research on fiber grating, sensors, a scheme of temperature sensitivity enhancement . Including the following aspects :1. Generally introduce the domestic and foreign development and application of sensors, FBG and the advantages of FBG sensors compared to the other sensors such as anti-interference capability, self-reference, absolute parameter of wavelength. 2. Analyze the physical mechanism that fiber grating is made of in use of photosensitive fiber material, and compare the two categories of effective methods: interference fabrication and point-by -point fabrication; it can be divided into uniform and non-uniform fiber grating.3. Analyze the optical transmission with the coupled-mode theory and analytical expression of fiber grating characteristic. The demodulation technology of signals is very important in Sensor System, the coding of which is wavelength. We analyze the application and principle of the currently used demodulation.4. We analyze the principle of FBG tuning , several schemes.Research on temperature sensor and sensitivity enhancement of FBG.The sensing FBG with low temperature sensitivity ,only 0.0lnm/℃,is commonly encapsulated by a drive material with high thermal expansion coefficient,which is hardly developed due to the restriction of driven material.A new scheme is proposed as shown in figure 1. The two surface material M 2 with low thermal expansion coefficient are glued to the ends of bottom material M 1 with high one.Then FBG is glued on the endpoints of M 2. This tuning device is designed to provide a equivalent drive material with a thermal expansion coefficient that can be changed not only by the materials , M 1and M 2,but also by changing the size of the device.So theoretically this tuning device can be designed with any high resolution according to practical requirements and break through the restriction of thermal expansion coefficient of drive material fundamentally.The fitting line of results is shown in figure 2. The experiment result indicates that within 4.6°C,the bragg wavelength moves 3.14nm .The temperature sensitivity is 0.70316 nm/°C,which is 70 times higher than that of the bare FBG and matches the theoretical result 0.7073nm/°C very well.Due to the 0.05 nm resolution of our optical spectrum analyzer , the resolution temperature measurement is <0.07°C. The linearity of the temperature response curves is0.9997.Because FBG is extended axially, there are not chirped effects of the reflection spectrum as polymer packaged that is hard for demodulation. The reflection spectrum remains same during the whole test.The FBG we use is written without coating. Its mechanical strength is low so that the tuning range is relatively small, which special written FBG with high mechanical strength would greatly increase. In addition, both shorter grating and more suitable material with high coefficient of thermal expansion are advantaged for temperature sensitivity coefficient and size of the device.The greatest advantage of this device is its adjustable temperature coefficient of sensitivity by designing the length. In the experiment, in order to change the length flexibly, we used clamp to replace glue to fix devices and achieved a change in the tuning efficiency, which accords with the theory. This study provides an important basis and reference values, and this device can be further improved by materials and production processes. In the field of high-precision measurement it is expected a great value.
Keywords/Search Tags:fiber grating, tunable, temperature sensitivity enhancement
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