Over the past 30 years, researchers from the fibre sensing community have been trying to improve the performance of distributed optical fibre sensors to sense parameters such as temperature, strain, pressure, etc. over long distances. Distributed optical fibre sensing has aided both the industry and the scientific research in various types of applications, for instance in the fields of civil engineering, medicine, energy industry and others. There are several widely utilized types of distributed fibre sensing techniques and among them are the sensors based on stimulated Brillouin scattering (more info), those on coherent Rayleigh backscattering (more info), and the ones, which are based on Raman scattering.
Other sensing techniques involve the inscription of Bragg gratings inside the sensing fibre. Fibre Bragg gratings (FBGs) have proven their high sensitivity as point sensors and accordingly received so much attention as promising candidates for distributed sensing. Having Fibre Bragg gratings written inside the fibres would allow having a full sensitivity to refractive index changes and the achievement of a reflected signal, which is stronger than the Rayleigh backscattered signal. Using these highly sensitive point sensors serially along the sensing distance, researchers were able to achieve quasi-distributed sensing at many points along the fibre, calling this structure Bragg grating arrays.
A fibre Bragg grating designates a periodic variation of the refractive index that is inscribed in the core of an optical fibre by exposing the latter to ultraviolet light as can be observed on Figure 1. Such structures are spectrally selective, as they exhibit a narrow reflectivity located around a specific wavelength that is determined by the Bragg condition.
We are currently focusing on developing a new distributed sensing system, which is based on the use of fibre Bragg gratings. Our aim is to achieve absolute measurements of different parameters such as strain, temperature, pressure, etc.
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Sancho, J., Chin, S., Barrera, D., Sales, S., & Thévenaz, L. (2013). Time-frequency analysis of long fiber Bragg gratings with low reflectivity. Optics Express, 21(6), 7171-7179.
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Thévenaz, L., Chin, S., Sancho, J., & Sales, S. (2014, June). Novel technique for distributed fibre sensing based on faint long gratings (FLOGs). In 23rd International Conference on Optical Fibre Sensors (Vol. 9157, p. 91576W). International Society for Optics and Photonics.