Intensity modulated refractive index sensor based on optical fiber Michelson interferometer

• We fabricated a high-sensitive refractive index sensor based on in-fiber Michelson interferometer.
• The sensor has a high sensitivity of −202.46 dB/RIU at the refractive index of 1.42.
• The proposed sensor overcomes the cross-sensitivity problem between refractive index and temperature via intensity modulation.
• The sensor could apply in the fields of chemical and biomedical sensing due to the advantages of short size (less than 8 mm) and ultra-simple sructure.

We demonstrated a refractive index (RI) sensor based on optical fiber Michelson interferometer (MI), which was fabricated by splicing a section of thin core fiber (TCF) to a standard single mode fiber with a core offset. Experimentally, such a MI-based RI sensor with a core offset of 8 μm and a TCF length of 3 mm exhibits a high resolution of 4.9 × 10−6 RIU and sensitivity of −202.46 dB/RIU, which is two or three times higher than that of intensity-modulated RI sensors reported previously. In contrast, our MI-based RI sensor is insensitive to temperature, thus overcoming the cross-sensitivity problem between surrounding RI and temperature. Moreover, intensity modulation, rather than wavelength modulation, was used in the proposed MI-based RI sensor, and the sensor also has the advantages of compact size (8 mm), simple structure, easy fabrication, and good repeatability.