实验发现，飞秒激光微加工光纤微腔时，两个侧壁与纤芯轴向并不完全垂直，刻蚀的非平行壁光纤微腔Mach-Zehnder干涉仪出现光程差随波长增大而线性减小、微腔总损耗随波长增大呈递减变化等反常现象．对此，提出非平行壁光纤微腔Mach-Zehnder干涉仪新模型并初步建立了分析理论，采用新模型及分析理论对新型微腔干涉仪特性进行了研究．数值分析了微腔底角、深度等参数对谱峰波长位置的影响，理论研究了微腔的光波传输损耗、吸收损耗、插入损耗、材料红外吸收损耗以及对干涉条纹对比度的影响，理论分析与实验结果相符．实验获得水溶液干涉条纹对比度高达35dB的非平行壁光纤微腔Mach-Zehnder干涉仪，将新型光纤微腔干涉仪用于流体传感，其蔗糖水溶液折射率传感灵敏度高达-12937．31nm／RIU．%It is found that two walls of fiber micro-cavity fabricated by femtosecond laser micromachining are not perpendicular to the fiber axis. Interference spectrum of the unparallel wall fiber micro-cavity Mach-Zehnder interferometer （MZI） shows abnormal character- istics, such as optical path difference decreasing linearly with wavelength increasing and the total loss decreasing with wavelength increasing. In this regard, we propose an unparalleled wall fiber micro-cavity MZI model and establish analytical theory. By using new models and theories, the new micro-cavity interferometer characteristics are studied, including that the effects of comer and depth on spectral peak wavelength are numerically analysed and transmission loss, absorption loss, insertion loss, infrared absorption loss of material as well as how they affect the interference fringe contrast are theoretically studied. Theoretical analyses and experimental results are in agreement with each other. For fluid sensing, a high-quality unparallel wall fiber micro-cavity MZI is fabricated. The interference fringe contrast of the fiber micro-cavity reaches up to 35 dB in water. Experimental results show that the sensor exhibits an ultrahigh RI sensitivities, as high as-12937.31 nm/RIU in aqueous solution of sucrose.
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