Abstract
Brillouin optical time-domain analysis (BOTDA) requires frequency mapping of the Brillouin spectrum to obtain environmental information (e.g., temperature or strain) over the length of the sensing fiber, with the finite frequency-sweeping time-limiting applications to only static or slowly varying strain or temperature environments. To solve this problem, we propose the use of an optical chirp chain probe wave to remove the requirement of frequency sweeping for the Brillouin spectrum, which enables distributed ultrafast strain measurement with a single pump pulse. The optical chirp chain is generated using a frequency-agile technique via a fast-frequency-changing microwave, which covers a larger frequency range around the Stokes frequency relative to the pump wave, so that a distributed Brillouin gain spectrum along the fiber is realized. Dynamic strain measurements for periodic mechanical vibration, mechanical shock, and a switch event are demonstrated at sampling rates of 25 kHz, 2.5 MHz and 6.25 MHz, respectively. To the best of our knowledge, this is the first demonstration of distributed Brillouin strain sensing with a wide-dynamic range at a sampling rate of up to the MHz level.
Highlights
In modern industry[1,2,3], geophysical research[4,5,6], the health monitoring of civil infrastructures[1,2], and the motion capturing of robot hands[7,8] and the human body[9], a truly distributed ultrafast measurement, are widely required for real-time monitoring of distributed strain or temperature information
The optical chirp chain (OCC) probe wave is composed of several short optical chirp segments, which are generated through frequency modulation by use of the frequency-agile technique
When the frequency span between the OCC probe wave and the pump pulse overlaps the Brillouin frequency shift (BFS) for the sensing fiber, the distributed Brillouin gain spectrum (BGS) along the fiber is revealed via the OCC probe wave in the time domain using only a single-shot pump pulse
Summary
In modern industry[1,2,3], geophysical research[4,5,6], the health monitoring of civil infrastructures[1,2], and the motion capturing of robot hands[7,8] and the human body[9], a truly distributed ultrafast measurement, are widely required for real-time monitoring of distributed strain or temperature information. As the frequency difference between these two waves approaches the local Brillouin frequency shift (BFS) of the FUT, the optical power transferred from the high-frequency light wave to the low-frequency light wave reaches a maximum. The Brillouin gain spectrum (BGS) can be obtained by sweeping the detuned frequency. The BFS, which is dependent on both applied strain and temperature along the FUT2,10,11,13–15, can be calculated by curve fitting the BGS. The process of frequency tuning to obtain the BGS is time-consuming. Distributed fast strain measurement has been previously realized using several techniques: Brillouin optical correlation-domain analysis (BOCDA)[3,16,17,18], Brillouin optical correlation-domain reflectometry (BOCDR)[3,19,20,21,22,23,24,25], and Brillouin optical timedomain analysis (BOTDA)[12,26,27,28,29,30,31,32]
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