2016 Fiscal Year Annual Research Report
ブリルアン光相関領域リフレクトメトリの性能向上と温度と歪の同時・分離・分布測定
| Project/Area Number |
16J05910
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| Research Institution | The University of Tokyo |
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Principal Investigator |
YAO YUGUO 東京大学, 大学院工学系研究科(工学部), 特別研究員(PD)
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| Project Period (FY) |
2016-04-22 – 2018-03-31
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| Keywords | Brillouin scattering / optical fiber / optical fiber sensor / lock-in detection |
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| Outline of Annual Research Achievements |
(1) We propose a Brillouin optical correlation domain reflectometry (BOCDR) with lock-in detection scheme. By designing a new system using the lock-in detection scheme and amplifying a small spontaneous Brillouin signal with the lock-in amplifier, a stable shape of Brillouin scattering spectrum is obtained. It is experimentally shown that the lock-in detection scheme enhances the SNR of the measurement compared with the ordinary method, and the measurement can be realized without averaging processing. By further introducing a periodical on/off phase modulation as a chopping for the lock-in detection, undesired optical background spectrum is effectively reduced.
(2) We propose the method of widening the frequency modulation amplitude Δf to over 5.4GHz in BOCDR system, by using an optical filter to exclude the Rayleigh scattering. A theoretical analysis regarding the influence on the Brillouin scattering is presented. Numerical simulations are performed when Δf is below or over the critical value. It is found that although the background noise becomes worse when Δf is over 5.4GHz, the spatial resolution is enhanced, and roughly obeys a linear relationship with the enhancement Δf.
(3) We have challenged our original idea of discriminative measurement of strain /temperature in BOCDR system using polarization maintaining optical fiber experimentally. Although we have not achieved the anticipated results, we could understand the drawbacks in the original idea and the system we have designed.
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| Current Status of Research Progress |
Current Status of Research Progress
2: Research has progressed on the whole more than it was originally planned.
Reason
We have demonstrated the Brillouin optical correlation domain reflectometry (BOCDR) with lock-in detection scheme experimentally, and published the results in the journal.
Also, we proposed the method of widening the frequency modulation amplitude Δf to over 5.4GHz in BOCDR. The simulation shows the linear relationship between the Δf and the spatial resolution.
We also challenged our original idea of discriminative measurement of strain /temperature in BOCDR system using polarization maintaining optical fiber experimentally. The major problems lie in the pump depletion induced by stimulated Brillouin scattering (SBS). The contradiction between the SBS and the distributed measurement cannot be solved at present. However, we have fully understood the problems and can seek for other solutions.
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| Strategy for Future Research Activity |
About the method of widening the frequency modulation amplitude Δf to over 5.4GHz in BOCDR, as the simulation has been completed, we will continue to verify the theory in the experiments, and try to publish a paper about this.
The discriminative measurement of strain /temperature in BOCDR system using polarization maintaining optical fiber is the major theme in this project. We will continue to endeavor to find the solutions for the existing problems. As the measurement of Brillouin dynamic grating (BDG) has been actually been realized, the remaining problem is to realize the distributed measurement. We will try to utilize high-nonlinear fibers and some other approaches in the new laboratory.
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Research Products
(2 results)
