Research On All Fiber Optic Sensor Based On Fiber Grating And MZ Interferometer

Optical fiber sensor has excellent sensing features: small volume, light weight, low cost and immunity to electromagnetic interference. Thereinto, fiber gratings are the most common,the most widely used devices in the field of optical fiber sensors. Whereas interferometric optical fiber sensors have become vital research objectives in many institutions because of their high sensitivity.In this thesis, several hybrid structures are presented to improve the traditional fiber sensors on the basis of the development trend of fiber sensors, the research on fiber grating sensors and interferometric optical fiber sensors. The primary details are as follows:1. An optical fiber sensor composed of a LPFG and a core-offset MZ interferometer is proposed based on the sensing characteristics of LPFG and the Mach-Zehnder interference theory. The resonance wavelength of LPFG and the interference fringe of MZ interferometer have different sensitivities of environmental RI and temperature. In the experiment, we selected two different dips(Dip1, Dip2) in the transmission spectrum formed by the intermodulation between LPFG and core-offset MZ interferometer, then get the temperature sensitivity of 0.0607 nm/ ℃ and 0.0563 nm/ ℃, respectively; RI sensitivity of-55.06 nm/RIU-18.025 nm/RIU, respectively. Simultaneous measurement of temperature and RI can be realized by using sensitive matrix. At the same time, the resolutions of temperature and environmental RI in the experiment are 0.32°C and 0.05%RIU, respectively.2. Another optical fiber sensor composed of a FBG and a MZ interferometer shaped by core-offset and peanut structure is proposed and demonstrated based on the sensing characteristics of FBG and the Mach-Zehnder interference theory. The Bragg wavelength of the FBG(dip1) and the interference fringe of the MZI(dip2) would shift differently with the variation of the temperature and RI. The temperature sensitivities of dip1 and dip2 are0.01228nm/℃ and 0.08329nm/℃, respectively. Dip1 is insensitive to RI whereas the sensitivity of dip2 is-26.965nm/RIU. Simultaneous measurement of temperature and RI can also be realized with the sensitive matrix. This cascaded sensor’s resolutions of temperature and environmental RI are 0.81°C and 0.2%RIU, respectively.3. A novel optical fiber sensor composed of a MZ interferometer fabricated by peanut-shape structure and a FBG is proposed based on the the Mach-Zehnder interference theory and sensing characteristics of FBG. Experimental results show that the temperature and micro-displacement sensitivities of MZ interferometer(dip1) and FBG(FBG_dip) are different.The temperature sensitivities of dip1 andFBGdip are 0.0909nm/℃ and 0.0121nm/℃,respectively. And the micro-displacement sensitivities of dip1 andFBG_dip are-0.0233nm/℃and 0.0122nm/℃, respectively. With the use of sensitive matrix, simultaneous measurement of temperature and micro-displacement can be realized. We have achieved the resolutions of temperature and micro-displacement with 0.26°C and 1.52μm, respectively.