Distributed optical fiber sensors based on Brillouin scattering are widely used to measure strain and temperature changes along optical fibers. However, noise interference and the physical properties of the sensing fibers have limited the ability to achieve high spatial resolution with these sensors. Researchers at Yokohama National University developed a strategy to enhance the spatial resolution of distributed temperature sensing using polymer optical fibers (POFs). The new approach to POF-based Brillouin optical correlation-domain reflectometry (BOCDR) demonstrates the successful detection of temperature changes over short distances. It could be used to develop high-resolution sensing applications for fields where short sensing lengths are suitable, such as health care and manufacturing. The researchers achieved distributed temperature sensing with high spatial resolution by exploiting the relationship between modulation amplitude and sensing fiber length. This figure illustrates the result of distributed temperature sensing using a perfluorinated graded-index plastic optical fiber (POF). The top diagram shows the structure of the sensing POF, including a 7.0-cm cooled section. The lower plot presents the measured Brillouin frequency shift distribution along the POF, clearly indicating the temperature change in the cooled region. Courtesy of Yokohama National University. “Our work addresses a critical challenge in distributed fiber optic sensing by pushing the boundaries of spatial resolution,” professor Yosuke Mizuno said. “By optimizing the modulation amplitude and fiber length, we have unlocked new possibilities for high-resolution temperature sensing, which could have important applications in fields such as structural health monitoring and industrial process control.” To increase the modulation amplitude beyond the conventional limit, the researchers reduced the fiber length relative to the measurement range, suppressing the Rayleigh scattering-induced noise. For this task, they used perfluorinated graded-index POFs, which have high temperature sensitivity and low strain sensitivity, making them well-suited for precise temperature measurements. The perfluorinated graded-index POF, which has relatively small core diameters of 50 to 120 µm and low optical propagation loss of about 0.25 decibels per meter, even at telecom wavelengths, is the only type of POF in which Brillouin scattering has been observed to be successful. The researchers used the technique in experiments to detect a 7.0-cm cooled section along a polymer fiber with high accuracy, thus demonstrating the ability to use the technique to successfully monitor temperature changes in practical applications. Additionally, the team achieved a theoretical spatial resolution in BOCDR of approximately 4.8 cm, surpassing previous limitations, using the technique. The team’s findings could open new possibilities for advancements in distributed sensing technologies. In future work, the researchers will explore how to extend the sensing length while maintaining high spatial resolution as well as how to use the technique to measure additional physical parameters such as pressure and humidity. The researchers also aim to refine the system for practical use in critical applications, including infrastructure monitoring and industrial diagnostics. “This breakthrough represents a major advance in fiber optic sensing technology,” Mizuno said. “We are excited to continue refining this approach and exploring its potential to address real-world challenges.” The research was published in Optical Fiber Technology (www.doi.org/10.1016/j.yofte.2025.104144).