Optical Fibers as a Key Element of Distributed Sensor Systems

Dear Colleagues,

Optical fibers coated with suitable protective layers are well-suited to distributed fiber sensing systems (DFSS) based on Rayleigh, Raman, and Brillouin back-scattering in small cross-sectional spaces and have found successful use in a wide variety of applications including civil structures, transmission lines, railway, down-hole monitoring, and others. To improve overall system performance, many of these DFSS use multiple fibers. For example, DFSS use both single mode (SM) and multimode (MM) fibers for simultaneous measuring of several parameters such as temperature and strain. The measured parameters are affected by wavelength-dependent loss, caused by splices, stress on the optical fiber, fiber degradation in hydrogen environments, and radiation; this loss can also vary over time. As a compromise of SM and MM, the quasi-single mode operation in few mode fibers (FM) allows for larger input pump power before the establishment of detrimental effects induced by fiber nonlinearities due to the well-controlled effective fundamental mode area. Moreover, FM supports only a few spatial modes and the coupling between the fundamental mode and higher order modes can be largely suppressed with careful design. The performance of FM DFSS is mainly determined by the optical parameters of the used FM fibers. 2-mode and 4-mode FM fibers were designed and fabricated for DFSS, but units do not limit the number of modes. One more advanced single optical structure containing more than one core is multicore (MC) fibers with small-diameter sensing elements that provide a high-density waveguide count. Using these fibers solves the problem of conduit and/or installation cable congestion and eliminates fiber-to-fiber positional error, as each waveguide in the MC fiber is permanently fixed in its parallel configuration with respect to other waveguides in the MC fiber structure. These MC fibers are typically coated with acrylate materials that are unsuitable for applications with higher temperatures and harsh environments, such as may be encountered in many industrial sensing applications, but new coatings, for example, ETFE, are also very useful.

Thus, this Special Issue aims to attract both theoretical and practical works that deal with optical fibers as a key element of DFSS. Submissions on but not limited to basic technologies of modelling, design, fabrication, and utilization of optical fibers for different, including extremal, applications of DFSS; the effect of optical fibers’ characteristics on the performance of DFSS in general; and problems regarding the interconnections of different fiber types are welcomed for this Special Issue. This Issue also focuses on the fiber construction of the modern DFSS multiplexing of three main back-scattering mechanisms—Rayleigh, Raman, and Brillouin—in conjunction with fiber Bragg gratings written in SM, MM, FM, and MC fibers. Review articles that describe the current state of the art are also welcome.

Prof. Dr. Oleg G. Morozov
Guest Editor

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