We propose and demonstrate an all-fiber liquid-level sensor using an in-line multimode-single-mode-multimode (MSM) fiber structure. A piece of single-mode fiber (SMF) is spliced to two sections of equivalent multimode fiber (MMF) which are used as both mode splitter and mode coupler. The cladding mode will be excited when the light propagates from MMF to SMF, and then it will be combined with fundamental mode to form a Mach-Zehnder interferometer (MZI) when the light propagates from SMF to the other MMF. The liquid level is detected by the selected resonant dips shift of the transmission spectrum. A sensing sensitivity of 264.6 pm/mm is achieved for the proposed sensor with an SMF length of 26mm. Due to its compact structure, easy fabrication, and high sensitivity, the proposed liquid-level sensor is attractive for practical applications in a variety of fields, such as marine detection and chemical processing.

我们提出并演示了使用串联多模单模多模（MSM）光纤结构的全光纤液位传感器。一条单模光纤（SMF）拼接到等效多模光纤（MMF）的两部分中，这些多模光纤既用作模式分离器又用作模式耦合器。当光从MMF传播到SMF时，将激发包层模式，然后当光从SMF传播到另一个MMF时，将与基本模式组合以形成Mach-Zehnder干涉仪（MZI）。液位通过透射光谱的选定共振倾角偏移来检测。所建议的SMF长度为26mm的传感器的感应灵敏度为264.6 pm / mm。由于其结构紧凑，易于制造且灵敏度高，