Weak fiber Bragg grating cascade sensor interrogation using microwave photonic filtering techniques

Abstract

Abstract:A microwave photonic technique is presented to interrogate a 5 m-long fiber, containing 9 mm-long weak FBGs having 10 mm grating separation, used as a distributed sensor. Hot-spots as small as 20 cm have been measured with an accuracy of 0.5 cm

An Interrogation Technique of FBG Cascade Sensors Using Wavelength to Radio-Frequency Delay Mapping

“…In principle, this resolution could be improved by enlarging the zero padding length up to a certain limit without requiring corrections of the linear relationship (3) (limit of 4 pm for a 1 nm of Bragg wavelength shift as stated in section II). Below this limit, an increase of resolution, a larger Bragg wavelength shift or both would require to take into account higher-order dispersion corrections to (3), and evaluate limitations due to overlapping of the impulse response peaks in (2). Besides, we have shown that, for a given resolution, the total RF measurement bandwidth required to implement the technique is scalable.…”

“…The method also shows an additional compromise between IFT processing time and resolution, through the length of the zero-padded signals. Finally, for a given processing effort, i.e., for a given temporal resolution in the impulse response ∆t', the resolution can also be improved simply by enlarging the total dispersion in (3).…”

“…Long, high-reflectivity FBGs have been used to detect hot spots [6], and a temperature sensor based on a 10-cm long continuous weak FBG has been reported [4]. In addition, in [3] it was presented a multiplexed sensor based on cascading weak FBGs, a scheme that does not require the difficult fabrication of long, continuous weak FBGs.…”

“…In this paper, we use a multiplexed FBG sensor composed of seven FBGs written in cascade where, in contrast to [3], the gratings are standard, not weak. The Bragg wavelength shift under environmental changes constitutes the sensing principle, and the proposed interrogation method can be viewed as a modification of the incoherent OFDR technique.…”

FBGs cascade interrogation technique based on wavelength-to-delay mapping and KLT analysis

“…In multiplexed sensors, known as quasi-distributed sensors as well, several discrete sensors, such as interferometers [3] or fiber Bragg gratings (FBGs) [4], are cascaded along a fiber link in order to perform a discrete distributed measurement.…”