Study of a large lateral core-offset in-line fiber modal interferometer for refractive index sensing

Abstract A large lateral core-offset in-line fiber modal interferometer was proposed in order to avoid the relative direction of the two core-offset joints affecting the interference performance. The RI sensing performances of the interferometers with different arm lengths were evaluated and compared with the small core-offset ones. The simulation and experimental results showed that the power remaining in the core mode decreased from 25 to 0.002% after the input light passing through the first core-offset joint as the core-offset displacement increased from 6 to 40 μm. Thus, the interference between the core mode and cladding mode within the enlarged core-offset interferometer was suppressed, and meanwhile the interference within the cladding modes was dominated. As the core-offset displacement was simply enlarged from 6 to 40 μm, the RI sensitivity was greatly improved from 43.97 to 123.40 nm/RIU. The proposed sensor is a cost-effective solution for RI sensing purpose, and exhibits the advantages of high sensitivity, simple structure and easy fabrication with only a fusion splicer.