Simultaneous measurement for liquid level and refractive index based on all-fiber modal interferometer

Yi Dai, Sisi Tan, Qizhen Sun*, Jianghai Wo, Zhilin Xu, Deming Liu

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


A simple fiber sensor capable of simultaneous measurement of liquid level and refractive index (RI) is proposed and experimentally demonstrated. The sensing head is an all-fiber modal interferometer manufactured by splicing an uncoated single-mode fiber with two short sections of multimode fiber. The interference pattern experiences blue shift along with an increase of axial strain and surrounding RI. Owing to the participation of multiple cladding modes with different sensitivities, the height and RI of the liquid could be simultaneously measured by monitoring two dips of the transmission spectrum. Experimental results show that the liquid level and RI sensitivities of the two dips are 245.7 pm/mm, -38 nm/RI unit (RIU), and 223.7 pm/mm, -62 nm/RIU, respectively. The approach has distinctive advantages of easy fabrication, low cost, and high sensitivity for liquid level detection with the capability of distinguishing the RI variation simultaneously.

Original languageEnglish
Pages (from-to)496-502
Number of pages7
JournalJournal of Modern Optics
Issue number6
Publication statusE-pub ahead of print - 2 May 2013


  • fiber-optic sensor
  • liquid level sensing
  • modal interferometer
  • refractive index sensing


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