The article "Distributed Fiber Optic Sensors for Tunnel Monitoring: A State-of-the-Art Review" by Zhang, Zhu, Jiang, and Broere provides an in-depth analysis of the application of distributed fiber optic sensors (DFOS) in monitoring and assessing the deformation behavior of tunnel infrastructure. DFOS systems, based on Brillouin and Rayleigh scattering principles, are highlighted for their ability to measure strain and temperature variations over long distances, making them suitable for monitoring underground infrastructure. The study discusses the installation of fiber optic cables along transverse and longitudinal directions to measure distributed strains and point displacements, emphasizing the importance of selecting appropriate sensing fibers, choosing the right measurement principles, designing effective sensor layouts, and establishing robust field sensor instrumentation. The review covers four key aspects: the selection of sensing fibers, the choice of measurement principles, the design of sensor layouts, and the establishment of field sensor instrumentation. It also provides practical suggestions for implementing DFOS in tunnel infrastructure monitoring. The article includes a comprehensive overview of DFOS systems, including their working principles, key technical metrics, and the selection of optimal sensing fibers. It further details the use of DFOS in monitoring bored tunnels, conventional tunnels constructed with the New Austrian Tunneling Method (NATM) or sprayed concrete lining (SCL), as well as immersed and cut-and-cover tunnels. The review highlights the advantages of DFOS over traditional monitoring techniques, such as point-wise sensors and geodetic measurements, which have limitations in providing spatially and temporally adequate information on structural deformations. DFOS offers a more comprehensive solution by capturing densely distributed strain and temperature information, making it a valuable tool for structural health monitoring (SHM) in tunnels. The article concludes with a detailed discussion of recent applications of DFOS in tunnel monitoring, emphasizing the rapid rise of DFOS in this field and its potential for future advancements.The article "Distributed Fiber Optic Sensors for Tunnel Monitoring: A State-of-the-Art Review" by Zhang, Zhu, Jiang, and Broere provides an in-depth analysis of the application of distributed fiber optic sensors (DFOS) in monitoring and assessing the deformation behavior of tunnel infrastructure. DFOS systems, based on Brillouin and Rayleigh scattering principles, are highlighted for their ability to measure strain and temperature variations over long distances, making them suitable for monitoring underground infrastructure. The study discusses the installation of fiber optic cables along transverse and longitudinal directions to measure distributed strains and point displacements, emphasizing the importance of selecting appropriate sensing fibers, choosing the right measurement principles, designing effective sensor layouts, and establishing robust field sensor instrumentation. The review covers four key aspects: the selection of sensing fibers, the choice of measurement principles, the design of sensor layouts, and the establishment of field sensor instrumentation. It also provides practical suggestions for implementing DFOS in tunnel infrastructure monitoring. The article includes a comprehensive overview of DFOS systems, including their working principles, key technical metrics, and the selection of optimal sensing fibers. It further details the use of DFOS in monitoring bored tunnels, conventional tunnels constructed with the New Austrian Tunneling Method (NATM) or sprayed concrete lining (SCL), as well as immersed and cut-and-cover tunnels. The review highlights the advantages of DFOS over traditional monitoring techniques, such as point-wise sensors and geodetic measurements, which have limitations in providing spatially and temporally adequate information on structural deformations. DFOS offers a more comprehensive solution by capturing densely distributed strain and temperature information, making it a valuable tool for structural health monitoring (SHM) in tunnels. The article concludes with a detailed discussion of recent applications of DFOS in tunnel monitoring, emphasizing the rapid rise of DFOS in this field and its potential for future advancements.