Reviewed by Lexie CornerMay 14 2025
Researchers at Yokohama National University have developed a dual-laser Brillouin optical correlation-domain reflectometry (BOCDR) system that uses two frequency-modulated lasers.
By adjusting the relative modulation phase between the pump and reference lasers, the system can detect strain and temperature along the entire length of an optical fiber.
The figure shows the Brillouin-gain-spectrum map obtained along a 13-m single-mode silica fiber. The upper diagram marks a ~1.1-m strained section. The lower color plot displays the corresponding shift in Brillouin frequency, confirming distributed strain sensing. Image Credit: Yokohama National University.
In a proof-of-concept experiment using a 13-m silica fiber, the team successfully measured Brillouin gain spectra (BGS) at approximately 200 MHz, more than 50 times lower than the conventional 11 GHz range.
The dual-laser approach makes BOCDR equipment simpler, more cost-effective, and easier to deploy, giving engineers a practical tool for long-term structural health monitoring, factory process control, and many other sensing tasks.
Yosuke Mizuno, Study Lead Author and Associate Professor, Yokohama National University
Distributed optical fiber sensors based on Brillouin scattering are widely used to measure strain and temperature. However, conventional BOCDR systems face three key limitations.
First, they typically require a physical delay line in one arm to define the measurement location. Second, the Brillouin signal appears around 11 GHz, necessitating the use of costly wide-band electrical spectrum analyzers or heterodyne detection systems. Third, varying the laser modulation frequency during scanning results in inconsistent spatial resolution along the fiber.
The newly developed dual-laser BOCDR system addresses all three challenges simultaneously. By independently modulating two lasers, it electronically shifts the correlation peak, eliminating the need for a physical delay line.
Optical heterodyne mixing reduces the Brillouin signal to approximately 200 MHz, allowing the use of standard, cost-effective radio-frequency equipment. Maintaining a fixed modulation frequency also ensures a uniform spatial resolution of about 0.36 meters along the entire fiber.
The researchers plan to enhance the system by increasing the scan rate, extending the sensing range beyond the current few tens of meters, and improving laser stabilization to support long-term measurement accuracy. They also intend to conduct field tests on real-world infrastructure, such as bridges, tunnels, and industrial pipelines, where access is limited to one end of the fiber.
We believe that the unique operation and advantages of the dual-laser system offer valuable potential for various applications. By providing a practical route to low-frequency, single-ended Brillouin reflectometry, this work not only introduces a fresh configuration but also lays a solid foundation for future research and real-world deployment.
Yosuke Mizuno, Study Lead Author and Associate Professor, Yokohama National University
The research team includes Guangtao Zhu from the Faculty of Engineering at Yokohama National University; Takaki Kiyozumi from the Graduate School of Engineering at the University of Tokyo; and Hiroshi Takahashi and Yusuke Koshikiya from the Access Network Service Systems Laboratories at NTT Corporation.
The study was partially supported by the Japan Society for the Promotion of Science (JSPS) through KAKENHI grants 21H04555, 24KJ1145, and 24KJ0908.
Journal Reference:
Zhu, G., et al. (2025) Dual-laser Brillouin optical correlation-domain reflectometry. Journal of Physics: Photonics. doi.org/10.1088/2515-7647/adcddb.