Rayleigh scatter based order of magnitude increase in distributed temperature and strain sensing by simple UV exposure of optical fibre

Abstract

We present a technique to improve signal strength, and therefore sensitivity in distributed temperature and strain sensing (DTSS) using Frequency domain Rayleigh scatter. A simple UV exposure of a hydrogen loaded standard SMF-28 fibre core is shown to enhance the Rayleigh back-scattered light dramatically by ten-fold, independent of the presence of a Bragg grating, and is therefore created by the UV exposure alone. This increase in Rayleigh back-scatter allows an order-of-magnitude increase in temperature and strain resolution for DTSS compared to un-exposed SMF-28 fibre used as a sensing element. This enhancement in sensitivity is effective for cm range or more sensor gauge length, below which is the theoretical cross-correlation limit. The detection of a 20 mK temperature rise with a spatial resolution of 2 cm is demonstrated. This gain in sensitivity for SMF-28 is compared with a high Ge doped photosensitive fibre with a characteristically high NA. For the latter, the UV enhancement is also present although of lower amplitude, and enables an even lower noise level for sensing, due to the fibre’s intrinsically higher Rayleigh scatter signal.

Enhancement of accuracy in shape sensing of surgical needles using optical frequency domain reflectometry in optical fibers

“…This is mainly due to the presence of dopant inside the fiber core and to the larger numerical aperture (NA) which collects more of the back-scattered light. However, as predicted by Loranger et al [22], UV exposed fibers (Hydrogen-loaded SMF-28 in this case) show a radical increase in the backscattered signal of about ~6300 times (~37dB). Contrary to the previous report on UV-exposed Rayleigh enhancement caused by the creation of color centers (defects) yielding a Rayleigh enhancement of ~20-25 dB [22], the fiber studied here actually had a strong and chirped (~5 nm) FBG written with a Bragg wavelength outside the scanned bandwidth for the distributed sensing.…”

“…However, as predicted by Loranger et al [22], UV exposed fibers (Hydrogen-loaded SMF-28 in this case) show a radical increase in the backscattered signal of about ~6300 times (~37dB). Contrary to the previous report on UV-exposed Rayleigh enhancement caused by the creation of color centers (defects) yielding a Rayleigh enhancement of ~20-25 dB [22], the fiber studied here actually had a strong and chirped (~5 nm) FBG written with a Bragg wavelength outside the scanned bandwidth for the distributed sensing. Scanning the laser close to the spectrum of the FBG allows a much higher signal, but limits the sensing length as the signal is quickly attenuated.…”

“…Figure 4 summarized these values for each fiber triplet studied, i.e. one triplet formed with SMF-28, another one formed with Redfern (Germanium-Boron doped, high NA) photosensitive fibers and the last one formed with UV exposed deuterium-loaded SMF-28 (UVE-SMF-28), as proposed by Loranger et al [22]. We can see that the fibers are not exactly positioned at 120° from each other (especially the SMF-28 assembly), but it is not a problem since the exact relative position can be evaluated and used in the shape reconstruction algorithm.…”

“…Using OFDR, the precision of the reconstructed shape has been shown to be 0.3mm. Also, Loranger et al [22] recently showed that Rayleigh scatter, on which strain measurements using OFDR is based, can be considerably enhanced by exposing fibers to a focused UV light. Therefore, this paper investigates the possibility of using high scatter UV exposed fibers to perform shape reconstruction of a typical biopsy needle (19 gauge (G)).…”

Recent Advances in Distributed Acoustic Sensing Based on Phase-Sensitive Optical Time Domain Reflectometry

“…Loranger et al reported a method to enhance the Rayleigh backscattering signal for improved SNR measurement in ϕ-OTDR systems [22]. The system is based on a costeffective method with reduced fabrication complexity based on exposing a single-mode fiber to UV light without requiring critical alignment compare to the writing of multiple FBGs.…”