Highly sensitive and in-line fiber sensors based on Mach-Zehnder Interferometer with sturdy structure

• Main Authors: Wen-Hao Zheng, 鄭文豪
• Other Authors: Jui-Ming Hsu
• Format: Others
• Language: zh-TW
• Published: 2015
• Online Access: http://ndltd.ncl.edu.tw/handle/83807178181595058217

碩士 === 國立聯合大學 === 光電工程學系碩士班 === 103 === This work designed and fabricated two kinds of Mach-Zehnder Interferometers (MZI) based on NCF-SMF-Up-taper and NCF-SMF-Taper structure. We investigated these two structures and compared the characteristics, mechanical strength, and sensitivity with each other. To comprehend the variation of the light field in the No-core fiber and the element immerged in the surrounding with different refractive index (RI), we used the simulation software BeamPROP to simulate the field. The simulated results advantage us to analyze and comprehend the principles of the devices. Afterward we began to fabricate the sensing components and then proceeded with our measurement. The tolerances of tensile force for Taper, Up-taper and SMF are compared by experiment. The experimental results indicated that the mechanical strength of the Up-taper is larger than that of the Taper. Furthermore, the mechanical strengths of the Up-taper and SMF are difficult to compare because the break point is not at the position of the element. The temperature experimental results indicated that the temperature sensitivities of the components can be increased by immerging the components into a surrounding with high thermo-optics coefficient (TOC) or thermal expansion coefficient (TEC). Moreover, the sensitivities of the components are different for the surrounding with different RI. For a surrounding material with the RI closing that of the fiber cladding, the temperature sensitivity should be severely enhanced. The experimental results indicated that high temperature sensitivities of 0.825 nm/°C and 1.070 nm/°C, respectively, were accomplished for the NCF-SMF-Up-taper and NCF-SMF-Taper MZIs surrounded in a material with a refractive index of around 1.45. For the surrounding index experiments, the interference spectra severely shift when the RI of the surrounding close to that of the fiber cladding. This result can be a mutual proof of the temperature experimental result. For the stress experiments, for the NCF-SMF-Up-taper MZI, the interference spectra blue shift and with a stress sensitivity of -2.5 pm/μɛ for increasing the axial tensile, for the NCF-SMF-Taper MZI, the interference spectra red shift and with a stress sensitivity of +2.75 pm/μɛ for increasing the axial tensile, The directions of spectra shift of the two MZIs are opposite, but the sensitivities are approximately equal. The proposed sensor has numerous merits of in-line applications, high sensitivity, easy fabrication, simple structure, compact size, and furthermore it is sturdy due to its high mechanical strength.