In-fiber quasi-Michelson interferometer for liquid level measurement with a core-cladding-modes fiber end-face mirror

• An in-fiber quasi-Michelson interferometer (IFQMI) is proposed and demonstrated for liquid level measurement.
• IFQMI consists of a short small-core fiber followed by a standard single-mode fiber terminated with a silver film.
• The device presents a water level sensitivity of 68.3 pm/mm.
• The device discriminates the refractive index of measured liquid with a high sensitivity of 1200.61 (pm/mm)/RI.

An in-fiber quasi-Michelson interferometer (IFQMI) working on reflection is proposed and experimentally demonstrated for liquid level measurement. The device consists of a short piece of small-core fiber (SCF) followed by a standard single-mode fiber (SMF) where its end-face is terminated by a thick silver film. A well-defined interference pattern is obtained as the result of the fiber-core mismatch and core-cladding modes interference. The proposed device with a 30 mm pigtail SMF at a wavelength of 1555 nm presents a water level sensitivity of −68.3 pm/mm. Besides, the proposed device can also discriminate the refractive index (RI) of liquid measured. The IFQMI with 50 mm-long SMF provides a high RI sensitivity of −1200.61 (pm/mm)/RIU.