How NTT is Using Light to Track Traffic: The Power of Optical Fiber Sensing

NTT (The Nippon Telegraph and Telephone Corporation is a Japanese telecommunications holding company headquartered in Tokyo, Japan. Wikipedia) and Partners Demonstrate Traffic Monitoring via Optical Fiber, Detecting Road Vibrations with Light Reflections

NTT, NTT East, NTT West, and NEC have jointly developed a new system that adds optical fiber sensing capabilities to the All Photonics Network (APN), a key part of the next-generation IOWN (Innovative Optical and Wireless Network) infrastructure. Utilizing the existing optical fiber network managed by NTT West, they demonstrated the ability to monitor wide-area traffic patterns and visualize real-time road conditions.

While optical fiber sensing has been explored before for traffic monitoring, this is the first instance of large-scale, multi-road planar monitoring. Traditional methods rely on camera footage for traffic observation, but this new system offers distinct advantages.

How Optical Fiber Sensing Works
Optical fiber sensing functions by sending light through fiber cables, where a portion of the light is reflected back due to interactions with the fiber’s material. These reflections vary based on the fiber’s condition, allowing the sensing device to analyze surrounding vibrations and detect changes, such as when vehicles pass over roads. By measuring the resulting shifts in reflected light, the system can calculate vehicle speed and traffic volume.

In this demonstration, the sensing device was connected to an APN-G (All Photonics Network Gateway), which manages light wavelengths and gathers data from multiple fiber cables. A special connection setup bypasses one-way devices like optical amplifiers, enabling the sensing device to detect reflected light effectively across a broad area.

Demonstration Roles

NTT devised and built the connection configuration for the IOWN APN sensing system, NTT East handled calibration of vehicle speed and counts, NTT West selected the monitoring points and provided equipment, while NEC supplied the APN-G device and analyzed the fiber vibrations to measure vehicle speed.