In the vast depths of the ocean, submarine cables carry over 95% of the world's international data traffic; In a coal mine at a depth of kilometers, the subtle deformation of the surrounding rock in the roadway may indicate the risk of collapse; A drop of crude oil leakage next to oil pipelines crossing mountains and rivers could trigger an ecological disaster. In these scenarios, a technology called "distributed fiber optic sensing" is quietly weaving an intangible perception network, using the "language" of optical signals to translate subtle changes in the environment in real time.

一、 Technical Principle: Dialogue between Light and Matter

The core of distributed fiber optic sensing technology lies in transforming the fiber optic itself into an "intelligent nerve" that combines sensing and transmission functions. When a laser pulse is injected into an optical fiber, the optical signal interacts with the glass lattice to produce three types of scattered light:

Rayleigh scattering (99.9%): sensitive to vibration, used for acoustic detection;

Raman scattering: temperature sensitive, used for fire warning;

Brillouin scattering: strain sensitive, used for structural deformation monitoring.

By demodulating the intensity, phase, or frequency changes of these scattered lights, the system can accurately locate environmental changes along the fiber optic cable at the meter or even millimeter level. For example, in earthquake monitoring, the Distributed Acoustic Sensing (DAS) technology based on Rayleigh scattering can convert 10 kilometers of optical fiber into 100000 "virtual microphones", capturing vibration signals ranging from 0.01Hz to 50kHz with a resolution of 10 meters, far exceeding the coverage range of traditional seismometers.

· 二、 Application scenario: "Perception Revolution" from Underground to Space

· 1. Guardians of the Energy Lifeline

· Oil and gas pipelines: In the "West East Gas Pipeline" project, the Φ - OTDR (phase sensitive photosensitive time domain reflection) technology is used to lay optical fibers along the pipeline to monitor third-party intrusion, leakage, and geological settlement in real time. In 2022, a monitoring case of a water pipeline in Xinjiang showed that the system successfully warned of three subsidence geological disasters with a positioning error of less than 1 meter.

· Power Fiber Optic Cable: State Grid has piloted the monitoring of icing on transmission lines based on BOTDR (Brillouin Optical Time Domain Reflectance). By analyzing changes in fiber optic strain, an early warning of excessive icing thickness can be given 24 hours in advance, reducing the risk of wire breakage.

· 2. Infrastructure "Medical Examiners"

· Bridge and Tunnel: The Hong Kong Zhuhai Macao Bridge uses OFDR (Optical Frequency Domain Reflectance) technology to monitor concrete cracks, with a spatial resolution of 0.1 millimeters and the ability to capture micro scale deformations.

· Coal mine safety: In the kilometer underground, the distributed fiber optic monitoring system can sense 0.01% of the surrounding rock strain changes in real time and warn of the risk of collapse. The application case of a mine in Shanxi in 2022 shows that the system provides a 3-hour advance warning for subsidence in goaf areas to avoid major accidents.

· 3. Marine and Geological "Scouts"

· Submarine fiber optic cable: Distributed fiber optic sensing technology can monitor earthquakes, tsunamis, and anchor damage in 4 million kilometers of submarine fiber optic cables worldwide. In the 2020 seismic monitoring of the South China Sea trough in Japan, the DAS system successfully captured the differential radiation characteristics of P-waves and S-waves, providing key data for the analysis of seismic source mechanisms.

· Geological exploration: In shale gas development, DAS technology in wells can record microseismic events, locate the extension direction of fracturing fractures, and improve oil and gas recovery.

· 4. Perception tentacles of smart cities

· Pipeline network monitoring: The Beijing Urban Sub center has deployed distributed optical fibers in water and gas pipelines to monitor pressure fluctuations and leaks in real time. The pilot project in 2024 showed that the system successfully alerted 5 cases of gas pipeline leaks, reducing the localization time from 2 hours using traditional methods to 30 seconds.

· Security warning: At borders, airports, and other perimeters, DAS systems based on interferometer structures can identify intrusion vibrations at a rate of 0.1 meters per second, with a false alarm rate of less than 0.1%.

三、 Technological breakthrough: the leap from "perception" to "cognition"

In recent years, distributed fiber optic sensing technology has achieved three major breakthroughs:

1. Multi parameter fusion: Brillouin Raman joint sensing technology can simultaneously measure temperature and strain, with a spatial resolution of up to 1 meter;

2. Ultra long distance monitoring: using dual end Raman OTDR technology, the monitoring distance exceeds 950 meters;

3. Intelligent algorithm empowerment: Combined with deep learning, the system can automatically recognize vibration signals such as earthquakes, vehicles, and human excavation, with an accuracy rate of over 95%.

4、 Future Outlook: Symphony of Light and Intelligence

With the integration of IoT and 5G technology, distributed fiber optic sensing is moving towards a new era of "integrated sensing":

Reuse of existing optical cables: By utilizing 500 million kilometers of communication optical fibers deployed globally, environmental monitoring can be achieved without the need for additional hardware;

Medical intervention application: OFDR based shape sensing technology can monitor the bending shape of catheters and endoscopes in real time, with an accuracy of 0.1 millimeters;

Space exploration: In spacecraft structural health monitoring, fiber optic sensors can withstand extreme temperature differences of -180 ℃ to 300 ℃ and sense real-time strain changes of 0.01%.

conclusion

From mines thousands of meters deep to satellites tens of thousands of meters high, from nanoscale structural deformation to kilometer level geological disasters, distributed fiber optic sensing technology is redefining the way humans perceive the world with the speed and accuracy of light. It is not only the "invisible guardian" of infrastructure security, but also the "sensory nerve" of the future intelligent society. In the dialogue between light and matter, it writes a magnificent chapter of technology guarding civilization.