[Enlarge image]Comb-enhanced distributed acoustic sensing. Top: Concept with applications. Bottom left: Sensitivity enhancement. Bottom right: Sensing distance expansion.
Fiber optic distributed acoustic sensing (DAS) offers a revolutionary technology for continuously mapping acoustic waves through a single fiber with high sensitivity. It provides high-density sensing of as many as tens of thousands of virtual points over a distance of up to tens of kilometers.1 As a huge “optical ear,” DAS has shown remarkable advances across a wide range of applications,2 including for the exploration of gas and oil, monitoring of pipeline networks and others. In recent years, the global market scale for DAS has reached billions of US dollars. So far, the single-frequency light sources commonly used in DAS have emerged as a significant bottleneck because both the sensitivity and sensing distance of DAS are primarily limited by their power and noise. Additionally, coherent fading of single-frequency lasers presents a critical challenge.
Soliton microcombs have been shown to be promising light sources for high-precision metrology.3 Frequency synthesis based on dual-microcombs offers a way to convert optical frequencies down to radio frequencies, providing exceptionally high resolution in heterodyne measurements for various applications.4 Thus, dual-microcombs could be used to break the bottleneck of single-frequency lasers in DAS.
In 2024, we proposed and verified the concept of coherently parallel DAS with integrated dual-soliton microcombs.5 A pair of microcombs are generated in two silicon nitride microrings on chip, forming a dual-comb light source. One comb serves as the probing light, while the other acts as the local reference, enabling direct heterodyne measurement. Our study shows that the response of each frequency channel can be linearly accumulated, demonstrating a tenfold sensitivity enhancement compared with conventional DAS with a single-frequency laser. Experimentally, we demonstrated sensitivity down to 560 fε/√Hz. Furthermore, microcombs enable higher power delivery free from nonlinearity in long fiber, leading to significant extensions in sensing distance. Our experiments show that the maximum sensing distance increases from 43 km to 72 km without any distributed amplification. Finally, the combination of multiple frequencies can also overcome the problem of coherent fading in DAS.
We believe that such comb-enhanced DAS is a breakthrough in realizing the next generation of DAS systems with ultrahigh sensitivity at long distances, offering great potential across a wide range of sensing applications, such as geophones, hydrophones and more.
Researchers
Yun-Jiang Rao, Baicheng Yao, Jian-Ting Li, Bing Chang, Jun-Ting Du, Teng Tan, Yong Geng, Heng Zhou, Yu-Pei Liang, Hao Zhang, Zeng-Ling Ran and Zi-Nan Wang, University of Electronic Science and Technology of China, China
References
1. Y. Rao et al. Photonic Sens. 11, 1 (2021).
2. A. Hartog, An Introduction to Distributed Optical Fiber Sensors, CRC Press (2017).
3. L. Chang et al. Nat. Photonics 16, 95 (2022).
4. B. Chang et al. Nat. Commun. 15, 4990 (2024).
5. J. Li et al. Sci. Adv. 10, eadf8666 (2024).