Fiber-Optic Salinity Sensing With a Panda-Microfiber-Based Multimode Interferometer

An ultrasensitive Panda-microfiber (PMF)-based multimode interferometer for salinity measurement is proposed and demonstrated. By inserting a section of PMF supporting a few modes into a conventional optical fiber system, an inline interference between the high-order modes of PMF, i.e., TE
₀₁
and TM
₀₁
, is realized. The sensitivity is as high as 2938.16 pm/
⁰
/
₀₀
and its resolution is up to 0.0014
⁰
/
₀₀
(0.0001 S/m), which is two magnitudes higher than other fiber salinity sensors. With the features of compactness, reconfigurability, stability, and compatibility with other fiberized components, PMF has great potential in tunable filtering, multiwavelength lasing, etc.