Abstract
The analysis of surrounding media has been a long-standing challenge of optical fiber sensors. Measurements are difficult due to the confinement of light to the inner core of standard fibers. Over the last two years, new sensor concepts have enabled the analysis of liquids outside the cladding boundary, where light does not reach. Sensing is based on opto-mechanical, forward stimulated Brillouin scattering (F-SBS) interactions between guided light and sound waves. In most previous studies, however, the protective polymer coating of the fiber had to be removed first. In this work, we report the opto-mechanical analysis of liquids outside commercially available, standard single-mode fibers with polyimide coating. The polyimide layer provides mechanical protection but can also transmit acoustic waves from the fiber cladding toward outside media. The comprehensive analysis of opto-mechanical coupling in coated fibers that are immersed in liquid is provided. The model shows that F-SBS spectra in coated fibers are more complex than those of bare fibers and strongly depend on the exact coating diameter and the choice of acoustic mode. Nevertheless, sensing outside coated fibers is demonstrated experimentally. Integrated measurements over 100 m of fiber clearly distinguish between air, ethanol, and water outside polyimide coating. Measured spectra are in close quantitative agreement with the analytic predictions. Furthermore, distributed opto-mechanical time-domain reflectometry mapping of water and ethanol outside coated fiber is reported, with a spatial resolution of 100 m. The results represent a large step toward practical opto-mechanical fiber sensors.
Original language | English |
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Article number | 016105 |
Journal | APL Photonics |
Volume | 4 |
Issue number | 1 |
DOIs | |
State | Published - 1 Jan 2019 |
Bibliographical note
Publisher Copyright:© 2019 Author(s).
Funding
The authors acknowledge the financial support of the European Research Council (ERC), Grant No. H2020-ERC-2015-STG 679228 (L-SID) and of the Israeli Ministry of Science and Technology, Grant No. 61047. H. Hagai Diamandi is grateful to the Azrieli Foundation for the award of an Azrieli Fellowship.
Funders | Funder number |
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Horizon 2020 Framework Programme | 679228 |
European Commission | |
Azrieli Foundation | |
Ministry of science and technology, Israel | 61047 |