Phase sensitive distributed vibration sensing based on ultraweak fiber Bragg grating array using double-pulse

Abstract

, "Phase sensitive distributed vibration sensing based on ultraweak fiber Bragg grating array using double-pulse," Opt. Abstract. A distributed vibration sensing technique using double-optical-pulse based on phase-sensitive optical time-domain reflectometry (Φ-OTDR) and an ultraweak fiber Bragg grating (UWFBG) array is proposed for the first time. The single-mode sensing fiber is integrated with the UWFBG array that has uniform spatial interval and ultraweak reflectivity. The relatively high reflectivity of the UWFBG, compared with the Rayleigh scattering, gains a high signal-to-noise ratio for the signal, which can make the system achieve the maximum detectable frequency limited by the round-trip time of the probe pulse in fiber. A corresponding experimental Φ-OTDR system with a 4.5 km sensing fiber integrated with the UWFBG array was setup for the evaluation of the system performance. Distributed vibration sensing is successfully realized with spatial resolution of 50 m. The sensing range of the vibration frequency can cover from 3 Hz to 9 kHz.

Enhanced Distributed Fiber Optic Vibration Sensing and Simultaneous Temperature Gradient Sensing Using Traditional C-OTDR and Structured Fiber with Scattering Dots

“…The sign of temperature change could be determined using other techniques. In previous work, where the fiber was structured with FBG arrays, the issue of indeterminable signal sign was treated by using multiple interrogator pulse wavelengths [29,30,31,33], which enabled actual phase recovery and thus determination of signed changes also for time-varying perturbations.…”

“…Many of the above-listed methods involve quite complex photonics on the sensing interrogator side, often with high demands on components like laser source, pulse shaper or detection path. In recent years, many investigations have been performed on the topic of how to improve C-OTDR DAS sensory performance from the side of the sensing fiber, proposing the use of modified optical fiber structured with large ultra-weak FBG arrays or continuous gratings [27,28,29,30,31,32,33,34,35,36,37,38,39,40]. Developments towards the demodulation of phase variations using discrete reflectors in optical fiber have, however, had a long history already.…”

Interrogation of Ultra-Weak FBG Array Using Double-Pulse and Heterodyne Detection

“…So a perturbation on fiber induces the variation of the interference signal from corresponding position. However, due to the fact that the intensity of the interference signal is related to the optical phase change via a trigonometric function, it is hard to demodulate the vibration from the intensity variation of the interference signal as stated in our previous paper [18]. Therefore, a coherent detection scheme is employed in this paper.…”

High performance interrogation by a composite-double-probe-pulse for ultra-weak FBG array

“…Recently, ultra-weak FBG (UWFBG) array based -OTDR have been proposed for the usage of high performance distributed vibration sensing [10][11][12][13][14] . In this technique, the UWFBG array embedded in the fiber is used as a set of "weak mirrors" to provide a stable and controllable reflected light signal in the specified location of the fiber.…”

“…Compared with the traditional -OTDR system, the reflected light signal obtained by the UWFBG array is more stable and has higher sensitivity, showing great potential in the field of distributed vibration sensing. In order to demodulate the signal in UWFBG array to realize distributed sensing, many methods have been proposed, including longsingle-pulse method, double-pulse method, three ports coupler method, coherent detection method, et al [11,12,14] However, none of these methods can avoid the influence of polarization fading during the superimposes between the optical signals reflected from adjacent UWFBGs or between the reflected light signal and the reference lightwave, because the SOP of the lightwave in the UWFBG array is uncontrollable. As a result, the visibility of the interference drops sharply, leading to detection dead zone.…”