Sensitivity property of a hetero-core-spliced fiber optic displacement sensor

A displacement sensor has been newly developed using a hetero-core spliced fiber optic element in a form of simple module structure and evaluated in terms of the accuracy, reproducibility, and sensitivity as an OTDR-based, tandem connected displacement detector, for the purpose of the full-scale environmental monitoring. The developed sensor module is designed to be sensitive to a relatively large displacement in the range 0-5 mm, for which a simple displacement-macrobending conversion mechanism in the module produces the change in the sensor transmission loss ranging from 0 to a few dB. The initial insertion loss only due to a hetero-core portion was 0.3 dB. The sensitivity showed a tendency proportional to the insertion length of hetero-core portion in the range from 1 to 2 mm. In contrast to conventional fiber distortion sensors such as FBG (fiber bragg grating) and BOTDR (Brillouin optical time domain reflectometer), the hetero-core technique introduced in this work shows no temperature dependence in its sensor principle since the use of hetero-core makes it possible that change in backward Rayleigh scattering can be successfully amplified with a relatively large curvature. The experiment promisingly showed sufficient reproducibility the sensing operation with the accuracy less than 0.1 % to the full span displacement of 5 mm.