Special Edition on System Components Series: Realizing Dreams — Yesterday, Today, Tomorrow— An Acoustic/Environmental Sensing Technology Based on Optical Fiber Sensors

Oki Electric was founded in 1881, as Japan’s first manufacturer of telecommunications equipment and devices. That year we succeeded in testing a prototype telephone and started on our way as “Oki, the acoustic technology company.” Since then, our history has spanned more than 120 years. From its start in acoustic technology, Oki Electric expanded into business activities related to marine industries, and our underwater acoustic sensor technology was built up through those businesses. In fact, it our technology in this field developed to the point where it is now world class. Currently this underwater acoustic sensor technology has started a major change toward optical fiber sensor technology. Why this change from acoustics to optics? In this paper we will look back on the start of our work in the application of underwater acoustic sensors and will review the development of our optical fiber sensor technology, yesterday and today. Looking at “tomorrow” also, we will discuss our view of the future of this technology. * System Solutions Company, Chief Engineer. The Sprouting of Research Seeds The important background factor in the arrival of optical fiber sensors on the world scene, needless to say, was the progress in the field of optical fiber technology itself. In 1970, Maurer, Kapron, and Keck of Corning, Inc. succeeded in developing a fiber which had a very low transmission loss of just 20dB/km. After that, R & D engineers around the world all came to recognize the superiority of optical fiber communication and optical fiber technology began making rapid advances. At the time that optical fibers, which are the transmission medium for optical fiber communication, first appeared on the world scene, one problem was the phenomenon that transmission characteristics change due to outside disturbances such as vibration or bending. For that reason, many people doubted whether optical communication was practical. However, some phenomena that are first thought of as “bad” may lead to the start of something good, when viewed differently. Some people wondered if that instability phenomenon couldn’t be positively harnessed to create a new kind of sensor. The research that was pursued by such individuals eventually led to optical fiber sensors. In the 1970’s, in the midst of the “cold war” rivalry between the US and the Soviet Union, the US Naval Research Laboratory (NRL) was groping for underwater acoustic technology different from earlier conceptions. In doing that, J. A. Bucaro, et. al., of the NRL had the novel idea that a new high-sensitivity underwater acoustic sensor could be achieved using optical fiber, and they began research and development in that direction in the mid1970’s. Very soon, in 1977, they published a report on experiments on the feasibility of achieving high sensitivity in an optical fiber underwater acoustic sensor. This paper was only 2 pages long, but it is thought to be the first technical paper in the world connecting optical fiber technology and underwater sounds. In Japan, the National Defense Academy, the leader in such research, began research and development on this subject in the latter half of the 1970’s. In this historical flow, in 1985 the Marine Acoustics Society of Japan formed a study committee on optical fiber underwater acoustic sensor with leading researchers from government, academia, and industry as members, and surveyed the technology trends abroad. As experts in underwater acoustics, we had had little exposure to optical fiber technology. In fact, our participation in that group was the first encounter with this technology. Like the Tortoise Who Had Trouble Getting Off the Starting Line After the study committee meetings of the Marine Acoustics Society of Japan, the participating companies all went to work on prototype development. In the midst of that flow, we debated exactly what we should do, but we, who were specialists in underwater acoustic sensors using piezoelectric transducers, did not have enough fundamental knowledge about optics. In terms of wavelength, for example, optical and acoustic waves are vastly different. We looked around us and could not even find books or measuring equipment related to optics. Moreover, at that time, we were the design group of a business unit, so we were busy