Shiro Ryu

Meiji University, Japan

Title: Optical time domain reflectometry for continuous time-domain measurement of Rayleigh backscattered light

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Biography

Shiro Ryu received a Ph.D. in electronic engineering from the University of Tokyo in 1993. After that, he researched coherent optical fiber submarine cable systems in KDD R&D Laboratories (1985-1995). After that, Dr. Ryu managed a research group in Japan Telecom and SoftBank Telecom R&D Laboratories regarding next-generation photonic networks (2000-2009). Then, he worked at SoftBank HQs (2009-2016) in charge of designing and deploying long-haul DWDM systems. He now serves as a Professor at the School of Interdisciplinary Mathematical Sciences of Meiji University. His current research interests are optical measurement techniques and optical wireless communication systems. 

Abstract

Research efforts have been made on the phase-sensitive optical time-domain reflectometry (?-OTDR). In ?-OTDR technique, the phase change of Rayleigh backscattered light at a certain point of the fibers due to a perturbation is detected by the intensity change of the backscattered light. One of the ?-OTDR technique problems is that a pulse repetition rate limits the maximum detectable bandwidth of the vibration below about 1kHz. However, it is known that high-speed vibrations of about 10kHz or more are generated in optical fibers laid in a real environment due to vibrations caused by trains running on bridges. Hence, the countermeasures for the above problem have been desired.

The OTDR technique using coherent heterodyne detection, in which signal light and local oscillator light sources are frequency swept linearly, is proposed and experimentally demonstrated to solve the problem above. Experimental results have shown that the technique makes it possible to continuously measure the backscattered light at a specific distance along the fibers in the time domain. 

We conducted an experiment by introducing a fiber stretcher that can apply high-speed vibration using a structure in which optical fibers are wound in multiple layers on a piezo element. In the experiment, we placed a fiber stretcher between two 20-km-long optical fiber reels and vibrated the fiber stretcher at a frequency of 140kHz. As a result of the investigation, we continuously observed the vibration component of 140kHz at the 20-km point in a time domain.