研究了一种基于错位和花生形结构的全光纤马赫-曾德干涉仪, 进行了液位和曲率的测量实验, 利用错位结构将纤芯模式激发到包层, 包层模式经过花生形结构被耦合到纤芯与原有的纤芯模式发生干涉。 包层模式对外界物理量如折射率、 应力的变化敏感, 导致透射光谱漂移。 波谷波长的漂移量与液位和曲率的变化成线性关系, 利用波谷的漂移实现液位和曲率的测量。 在液位实验中, 在水位变化范围为1.00～5.00 cm时, 波谷向短波方向漂移, 灵敏度最高为-0.68 nm·cm-1, 线性拟合度为0.995 4。 在曲率实验中, 曲率的变化范围为0.3～1.2 m-1时, 波谷向长波方向漂移, 灵敏度最高为22.47 nm·m, 线性拟合度为0.986 4, 表现出较高的灵敏度。 错位结构和花生形结构被用于组成马赫-曾德干涉仪, 用普通的光纤熔接机和普通单模光纤即可熔接, 结构和制作方法简单, 灵敏度高, 尤其在曲率的测量中表现出较高的灵敏度。

A new in-fiber Mach-Zehnder interferometer (MZI) based on lateral-offset and peanut shape structure is proposed and demonstrated for the measure of curvature and liquid level. The sensor consists of lateral-offset structure and peanut shape structure. A section of single mode fiber (SMF) is spliced between them. A part of core mode in the single mode fiber is excited to cladding modes by lateral-offset. The cladding modes are re-coupled to the core mode by peanut-shape structure and get interference with the core mode. A high-quality interference spectrum with a fringe visibility of about 12 dB is observed. The effective refractive indices of cladding mode would change with the external environment parameters, which further bring about a shift of the interference fringes. The liquid level or curvature can be measured by record the shift of the valley, because the shift of the valley shows a linear dependence with the variation of the liquid level or curvature theoretically. In the water level experiment, the water level changes from 1.00 to 5.00 cm and the wavelength valley shows a red shift. The sensitivity of the MZI with a length of 6.10 cm is -0.68 nm·cm-1. In the curvature experiment, the curvature changes from 0.3 to 1.2 and the wavelength valley shows a blue shift. The sensitivity of the MZI with a length of 2.10 cm is 22.47 nm·m. The lateral-offset structure and peanut shape structure are spliced to fabricate the MZI. The sensitivity of the MZI is high, especially in the curvature measurement, it is higher than that of other fiber curvature sensors. Moreover the MZI presented in this paper has advantages of low cost and easy fabrication, which can be a potential application in the liquid level and curvature measurement.