基于错位和花生形结构的全光纤马赫-曾德干涉仪的研究

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。

All-Fiber Mach-Zehnder Interferometer Based on Lateral-Offset and Peanut Shape Structure

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 struc-ture.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 interfer-ence with the core mode.A high-quality interference spectrum with a fringe visibility of about 1 2 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 measure-ment,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.