Effect of humidity on optical fiber distributed sensor based on Brillouin scattering

Abstract

In real sensors, the crosstalk or undesirable crossed sensitivities must be minimized. Distributed Brillouin sensing is a very useful technique to measure fluctuations of temperature along an optical fiber. However, the later measurement can be influenced by the humidity on the fiber; therefore its effect must be minimized. Because the aforementioned, the Brillouin frequency changes with the humidity. Thus, for a given temperature on a distributed fiber sensor such variations have been investigated. The experimental results obtained using three different types of single mode fibers with 1000m length, at 25ºC are reported in this paper.

Brillouin Distributed Fiber Sensors: An Overview and Applications

“…Also, it is important to remark that there is an exponential relationship between the Brillouin power gain and the Brillouin gain spectrum, which is maximized at ν B value. According to the mathematical description presented in (1), Brillouin scattering is strongly dependent on thermodynamical variables [8][9][10][11][12]. The dielectric constant varies according to the pressure wave that is generated and which travels along the medium.…”

Optical Fiber Sensing Cables for Brillouin-Based Distributed Measurements

“…A significant nonlinear sensitivity of the BFS value on relative humidity variation (Rh) was also observed [31] and must be taken into account because it can cause, in principle, a significant error for common variations of the environmental humidity. In particular, a BFS sensitivity to moisture variation of <0.025 MHz/%Rh is reported, as well as a decreasing influence at increasing humidity levels [31].…”

“…A significant nonlinear sensitivity of the BFS value on relative humidity variation (Rh) was also observed [31] and must be taken into account because it can cause, in principle, a significant error for common variations of the environmental humidity. In particular, a BFS sensitivity to moisture variation of <0.025 MHz/%Rh is reported, as well as a decreasing influence at increasing humidity levels [31]. This effect is likely to stem from the swelling of the fiber coating due to the absorption of moisture, as is known for the polymer coating of fiber Bragg gratings and can be suppressed using an optical fiber with a seamless sealed protection, such as those used in most commercial telecom cables for outdoor use and all the cables specifically designed for Brillouin temperature sensing.…”

Optimising the design, cost, and performance of a distributed humidity and temperature fibre sensor

“…In 2008, Galindez et al studied the RH effect on the Brillouin frequency shift using a Brillouin distributed sensor with 10 metres of spatial resolution. 5,6 In this study, the authors investigate the variation of the Brillouin frequency shift at different RH levels at 25°C using three distinct types of single-mode fibres. More recently, P. J. Thomas and J. O. Hellevang presented, in 2017, a study about the characteristics of a 64 metres long distributed RH sensor with centimetre spatial resolution and P. Stajanca, in 2019, presented a simultaneous humidity and temperature monitoring solution.…”