Physics

Scientists demonstrate advanced low-coherence BOCDR system using periodic pseudorandom modulation

This figure shows the results of distributed strain sensing over a length of approximately 100 m of optical fiber utilizing BOCDR with periodic pseudorandom modulation. The diagram above shows the structure of the sensing fiber, which includes two tightly wound 47-meter sections and a 10-centimeter taut section near the end. The middle plot shows the distributed Brillouin frequency shift along the entire measurement range in response to the applied strain. The bottom plot shows a magnified view of the strain section and clearly shows the Brillouin frequency shift in response to 10 centimeters of strain. These results demonstrate the high spatial resolution and extended measurement range achieved by the proposed method. Provided by: Yokohama National University

Scientists demonstrate a low-coherence Brillouin optical correlation domain reflectometry (BOCDR) system that overcomes long-standing challenges related to spatial resolution and measurement range when mapping strain and temperature distributions along optical fibers succeeded.

Their research is published in the Journal of Lightwave Technology.

“We addressed the persistent challenge of balancing spatial resolution and measurement range with a unique fiber optic distributed strain sensing technology called BOCDR,” said Yosuke Mizuno, associate professor at Yokohama National University. “Our objective was to develop a more efficient system that overcomes this trade-off without relying on complex components such as variable delay lines.”

Traditional BOCDR techniques have advantages such as operation by light injection from one end of the sensing fiber, relatively high spatial resolution, and the ability to randomly access sensing points. However, we also face a trade-off between spatial resolution and measurement range. Previous efforts to alleviate this problem have included special schemes such as time gates, dual modulation, and chirp modulation.

However, these methods do not completely eliminate fundamental trade-offs. Researchers have begun to focus on the use of low-coherence BOCDR using randomly modulated light sources, but this approach requires a variable delay line to scan the measurement location and limits the measurement range. will be done.

To address this limitation, a research team including collaborators from NTT Corporation, with support from Dr. Kohei Noda from the University of Tokyo, developed a low-coherence BOCDR system based on periodic pseudo-random modulation, and the concept We have proven the proof. Surgery.

They started by investigating the output spectrum of the light source based on the modulation parameters using a delayed self-homodyne method. This method solves the traditional trade-off between spatial resolution and measurement range and shows the potential to extend measurement range while maintaining high spatial resolution.

We then demonstrated that strain distribution along an optical fiber can be measured under multiple conditions without the use of variable delay lines. Through simulation and experiment, their results showed that this new method performs more accurate distributed strain measurements than traditional BOCDR techniques, with the added advantage of not requiring variable delay lines. Additionally, their method is free from systematic errors associated with amplitude-modulated frequency modulation (AM-FM) phase delays.

The research team’s low-coherence BOCDR applied periodic pseudorandom modulation generated by an arbitrary waveform generator directly to the light source’s drive current to achieve modulation of its output frequency. While traditional low-coherence BOCDR is based on aperiodic random modulation, this new method creates multiple correlation peaks (measurement points) along the fiber under test. This makes it possible to sweep non-zero-order correlation peaks along the fiber without the need for variable delay lines.

“The most important result from our research is the successful demonstration of a low-coherence BOCDR system based on periodic pseudorandom modulation,” Mizuno said. “This approach not only maintains high spatial resolution and extends the measurement range, but also simplifies system design and makes it more practical for real-world applications.”

The team’s proof of concept using low-coherence BOCDR technology sets the stage for future exploration of system optimization and detailed performance analysis, including improved spatial resolution, extended measurement range, increased measurement speed, and improved accuracy. Arrange.

Looking to the future, the team aims to refine this low-coherence BOCDR technique to further improve performance in terms of resolution, range, and speed.

“Ultimately, we aim to see this method widely adopted for accurate strain sensing in critical applications such as structural health monitoring and industrial diagnostics,” Mizuno said.

The research team includes Kenta Otsubo, Kotao Zhu, Takaki Kiyosumi, and Yosuke Mizuno from the Yokohama National University School of Engineering. Kohei Noda, Graduate School of Engineering, University of Tokyo. Mr. Hiroshi Takahashi and Mr. Yusuke Koshikiya of NTT Corporation’s Access Network Service Systems Laboratories.

Further information: Kenta Owari et al, Low-Coherence Brillouin Optical Correlation- Domain Reflectometry Based on Periodic Pseudo-Random Modulation, Journal of Lightwave Technology (2024). DOI: 10.1109/JLT.2024.3436928

Provided by Yokohama National University

Citation: Scientists demonstrate advanced low-coherence BOCDR system using periodic pseudorandom modulation (October 1, 2024) https://phys.org/news/2024-10-scientists-advanced-coherence-bocdr Retrieved October 1, 2024 from -periodic.html

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