Recent progress in optical fiber sensors based on Brillouin scattering at university of Ottawa

Abstract

The distributed sensor is proven to be a powerful tool for civil structural and material process monitoring. Brillouin scattering in fiber can be used as point sensors or distributed sensors for measurement of temperature, strain, birefringence and vibration over centimeters (Brillouin grating length) for point sensor or the pulse length for the distributed sensor. Simultaneous strain and temperature measurement with a spatial resolution of 20 cm is demonstrated in a Panda fiber using Brillouin grating technique with the temperature accuracy and strain accuracy of 0.4 ℃ and 9 µε. This technique can also be used for distributed birefringence measurement. For Brillouin optical time domain analysis (BOTDA), we have developed a new technique to measure differential Brillouin gain instead of Brillouin gain itself. This technique allows high precision temperature and strain measurement over long sensing length with sub-meter spatial resolution: 50-cm spatial resolution for 50-km length, using return-to-zero coded optical pulses of BOTDA with the temperature resolution of 0.7 ℃, which is equivalent to strain accuracy of 12 µε. For over 50-km sensing length, we proposed and demonstrated frequency-division-multiplexing (FDM) and time-division-multiplexing (TDM) based BOTDA technique for 75-km and 100-km sensing length without inline amplification within the sensing length. The spatial resolution of 2 m (100 km) and Brillouin frequency shift accuracy of 1.5 MHz have been obtained for TDM based BOTDA and 1-m resolution (75 km) with Brillouin frequency shift accuracy of 1 MHz using FDM based BOTDA. The civil structural health monitoring with BOTDA technique has been demonstrated. Distributed fiber sensors based on Brillouin scatteringFor over two decades, distributed optical fiber sensors based on Brillouin scattering have gained much interest for their potential capabilities of monitoring temperature [1] and strain [2] in civil and structural engineering, environmental monitoring, and geotechnical engineering. Brillouin scattering occurs as a result of refractive-index fluctuations caused by acoustic waves resulted from thermally generated sound waves, and such thermal agitation is capable of scattering incident lightwaves with shifted frequencies. Stimulated Brillouin scattering (SBS) enhances the Brillouin scattering in a Brillouin optical time domain analysis (BOTDA) [3][4][5][6][7][8] with intense signal and better spatial resolution comparing with a spontaneous scattering based Brillouin optical time domain reflectometry (BOTDR) [9][10][11]. At present, there are two schemes to realize a BOTDA, including Brillouin gain [3][4][5] and Brillouin loss [6][7][8]. In a Brillouin-gain-based

Structural Health Monitoring of the Scaffolding Dismantling Process of a Long‐Span Steel Box Girder Viaduct Based on BOTDA Technology

“…e BOTDR-based distributed optical fiber sensor detects self-emitted Brillouinscattered light, but due to the weak optical power, it is difficult to achieve high-precision, long-distance distributed sensing [15]. e BOTDA-based distributed optical fiber sensor utilizes the stimulated Brillouin scattering between direct-current (DC) detection light and pulsed pumping light to amplify the detection light through the stimulated Brillouin effect, which achieves characteristics, such as high-strength received signals, high measurement accuracy, and wide dynamic range [17]. Kwon [18] measured the change in distributed temperature on the building under construction by fiber optic sensors.…”

“…However, limited research has applied Brillouin optical time-domain analysis in the dismantling process of bridge supports. is technology provides high-precision temperature and strain measurements with submeter spatial resolution on the long sensing length [16,17]. Another advantage of BOTDA technology is that the same optical fibers can be reused many times.…”

“…When the frequency difference between the pulsed light and the continuous light is equal to the Brillouin frequency shift of a certain interval in the fiber, there is a stimulated Brillouin amplification effect, and energy transfer occurs between the two beams [14]. According to the relationship between the fiber Brillouin frequency shift and the strain and temperature of the fiber, the frequencies of the two lasers are continuously adjusted, and the continuous optical power coupled from one end of the fiber is monitored to determine the frequency at the maximum energy transfer in each region of the fiber [17]. e frequency shift can be input into equation (1) to obtain the required strain or temperature information:…”

“…en, the measured bridge data are transmitted to the network layer and further analyzed and processed. e results of the final analysis are transmitted to the application layer, i.e., the deformation information is transformed into a report or graphical form that is easy to view and analyze, and the bridge is further analyzed [17].…”

Bi-Directional Brillouin Optical Time Domain Analyzer System for Long Range Distributed Sensing

“…By scanning the pump-probe frequency difference, the Brillouin gain spectrum (BGS) can be re-constructed to determine the distribution of Brillouin frequency shift (BFS), and hence the temperature and/or strain information along the fiber can be retrieved. In recent decades, driven by the increasing demand for structural health monitoring by distributed temperature and/or strain sensing in civil, transportation, aviation, and military applications, many works have been done to enhance the system performance in terms of spatial resolution and sensing range [2]. However, it has been shown that it is difficult to extend the sensing range while maintaining a high spatial resolution, since the BOTDA system suffers from pump depletion [3], non-local effects [4], modulation instability [5], and other nonlinearities.…”