Fernández Vallejo, MontserratRota Rodrigo, SergioLópez-Amo Sáinz, Manuel2014-05-262014-05-2620111424-822055810.3390/s110908711https://academica-e.unavarra.es/handle/2454/10609We propose and demonstrate two ultra-long range fiber Bragg grating (FBG) sensor interrogation systems. In the first approach four FBGs are located 200 km from the monitoring station and a signal to noise ratio of 20 dB is obtained. The second improved version is able to detect the four multiplexed FBGs placed 250 km away, offering a signal to noise ratio of 6-8 dB. Consequently, this last system represents the longest range FBG sensor system reported so far that includes fiber sensor multiplexing capability. Both simple systems are based on a wavelength swept laser to scan the reflection spectra of the FBGs, and they are composed by two identical-lengths optical paths: the first one intended to launch the amplified laser signal by means of Raman amplification and the other one is employed to guide the reflection signal to the reception system.application/pdfeng© 2011 by the authors; licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution license (http://creativecommons.org/licenses/by/3.0/).Sensor multiplexingRemote sensingRaman amplificationFiber Bragg gratings (FBGs)Erbium doped fiberSensor systemNoiseScatteringStraininfo:eu-repo/semantics/articleinfo:eu-repo/semantics/openAccess