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An overview of truly remote fiber optic sensors is presented in this work. It starts with a brief introduction of fiber optic sensor networks, showing their advantages and multiple applications. Then, the definition of truly remote networks is provided, and their main challenges discussed, such as increasing the sensing distance and the number of sensors interrogated. Several multiplexing techniques have been compared, such as wavelength, time and coherence division multiplexing. In relation to this, the most recent works showing multi wavelength fiber lasers for wavelength division multiplexing have been grouped and their versatility analyzed. Finally, recent and relevant truly remote fiber optic networks have been gathered and some of the most representative schemes explained in detail, comparing their multiplexing capability and the remoteness of the monitored sensors. Random distributed feedback fiber lasers form part of a number of these schemes, proving the suitability of this type of lasers for their use in ultra-long truly remote sensing applications.

In this paper, the experimental study and characterization of a novel real-time switchable multi-wavelength fiber laser has been carried out. Two different gain materials, such as a 50 km SMF and a 2.5 km DCF fibers were characterized and compared, respectively. The MWFL can generate any wavelength combination with an emission lines distance of 50, 100 and 200 GHz fitting the ITU grid specifications. By using both Er-doped fiber and Raman amplification, a ~30 nm wide lasing window at the C band can be utilized to create up to 30 different lasing wavelengths into the ITU Grid, that can be switched automatically and in real-time when desired. Utilization of such a laser for versatile interrogation of different sensing networks is also shown. Index Terms-. Switchable multi-wavelength fiber laser, random distributed feedback .