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Introduction to the Issue on Optical Sensors


T is a great pleasure to serve as the Guest Editor along with Dr. Kazuo Kyuma on the JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS Special Issue on Optical Sensors. This unusual topic for a journal of quantum electronics is really not out of place if we remember that there has been a fusion of the principles applied in optics with those in the measurement of physical quantities. To this end, the collection of papers presented here will reflect this trend, drawing from the rich developments in the field of fiber-optic communications, nonlinear optics, fiber optics, and fiber Bragg gratings (FBGs). For example, the reader will find techniques first applied elsewhere being examined more closely to take advantage of the coherence properties of light in the case of the paper on coherence tomography. This is an area that is taking on a new dimension for the detection of abnormalities in deep soft tissue, a subject fraught with difficulties when faced with defects of small dimensions. The simplicity of using a fiber-optic probe in the shape of a Michelson interferometer is immediately apparent. Another technique is clearly demonstrated for the measurement of layered media, utilizing the optical coherence function by scanning the frequency of a laser in a stepwise fashion and by the use of Fourier transforms. Nonlinear techniques have also been adapted with millimeter waves for imaging. Although the resolution is shown to be proportional to the wavelength of the field, it is recognized that a similar approach may be applied in the optical domain to increase dimensional sensitivity. Composite materials also pose a serious problem when sensing the distribution of temperature and vibration. Interferometric techniques applied here can pay dividends when vibration must be detected, while fiber optics allow the input and output connections to the position of the sensors. A novel multichannel sensor comprising several interferometic outputs, each with a well-defined, but related phase, may be used to extract temperature and vibration information, as demonstrated by Garcia Souto and Rivera. One of the authors (Garcia Souto) applies interferometric techniques to also detect submicron vibrations within the magnetic cores of power transformers. On the other hand, the invited paper by Schenk et al.demonstrates some novel features for micromechanical scanning over large dimensions, with one application on pattern generation. It should be quite clear that such devices could find sensing applications in harsh environments in which accelerations in the order of several hundred would cause some considerable discomfort for most conventional instrumentation. This paper

Publisher Item Identifier S 1077-260X(00)11229-8.

demonstrates just how accessible this technology is becoming, again drawing heavily from developments in the optical communications field. It is hard to find any journal on sensing that does not include papers on FBGs. This technology has found niche applications in the most unusual places. Along with this has been the reapplication of coherent techniques to extract the information from an array of sensors to build a strain profile with a high resolution of 2 . With stabilization posing a major problem for sensor designers, it is shown in another paper how phase drift may be compensated while sensing electric current using spun highly birefringent fiber, using simple passive techniques, while maintaining sensitivity to the measurand. Time-division multiplexing of an array of Bragg gratings is the topic of a paper by Chan et al.. Here, the aim is to maintain high resolution while increasing the number of sensing elements, and the results of computer simulations indicate that high sensitivity may be maintained for 20 gratings using commercial Mach-Zehnder modulators. Also demonstrated is an interrogation system for the interrogation Bragg gratings by changing the selectivity of a wavelength division multiplexer, maintaining microstrain resolution while detecting extensions in the region of millistrain. A paper by Zubia et al. shows the use of plastic optical fibers (POF) in a harsh environment (in this case, the top of a mountain where lightning strikes, which poses a hazard for electric sensors in anemometers), taking advantage of the economy of POF while maintaining electric isolation. Finally, another paper uses POF for intensity sensing applications. Chandy et al.demonstrate the ease with which a POF may be prepared by slicing the cladding of the fiber to allow a biofilm on the surface to interact with the optical evanscent field of the mode in the core. The advantage of such a fiber is in the ease of preparation, disposability, and relative insensitivity to temperature changes, making it a possible platform on which to build a sensor. As Guest Editors, we hope that the reader will benefit from the varied content of this issue and that it will stimulate discussion while adding to the better understanding of sensors and an appreciation of the widely different applications possible. RAMAN KASHYAP, Guest Editor Corvis Canada Ville St. Laurent, QC, Canada H4T 1N1 KAZUO KYUMA, Guest Editor Mitsubishi Electric Corp. Advanced Tech. Research and Development Center Amagasaki, Japan

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Raman Kashyap has worked in the field of fiber optics for over 20 years. He received the B.Sc. in electronics engineering from King’s College, University of London, London, U.K., in 1974, and the Ph.D. in physics from Essex University, Colchester, U.K., in 1990. He has worked in a number of areas including fiber optic sensors, devices, nonlinear optics, measurements, and optical fiber transmission. He was with BT Research Laboratories, Martlesham Heath, U.K., for 25 years, where he initiated research on fiber Bragg gratings and pioneered techniques to write long gratings ( 1 m) using phase masks. He is the author of approximately 200 journal and conference papers and has presented invited papers at several international conferences. He has filed/been granted approximately 25 patents and is the author of a book on Fiber Bragg Gratings. Dr. Kashyap was conference Co-Chair for the last OSA meeting on Bragg gratings, and is the General Chair for the meeting to be held next year.

Kazuo Kyuma (M’87–SM’94–F’97) received the B.S., M.S., and Ph.D. degrees, all in electronic engineering, from the Tokyo Institute of Technology, Tokyo, Japan, in 1972, 1974, and 1977, respectively. He joined Mitsubishi Electric Corporation, Japan, in 1977. Since 1998, he has been the Manager, Business Promotion Project, Artificial Retina, System LSI Division. From 1985 to 1986, he was a Visiting Researcher at the California Institute of Technology, Pasadena. From 1993 to 1995, he was Head of the Department of Neural and Parallel Processing Technology, Semiconductor Basic Laboratory, and from 1995 to 1998, he was Head of the Advanced Technology Research and Development Center, Mitsubishi Electric Corporation, Amagasaki, Japan. He has successively held Guest Professorships at the Tokyo Institute of Technology, Tokyo, Japan, Keio University, Keio, Japan, Kobe University, Kobe, Japan, and Hokkaido University, Hokkaido, Japan. His research interests cover optoelectronics, advanced LSI systems, and neuro-computing, which includes artificial retina, optical and VLSI neurochips, theoretical modeling and applications of neural networks, and optical fiber sensors. He is the author of more than ten books and of more than 180 published papers. Dr. Kyuma is a Fellow of the Optical Society of America, is on the Editorial Board of the International Neural Network Society, and is a member of the Institute of Electronics, Information and Communication Engineers, the Japan Society of Applied Physics, and the Institute of Image Information and Television Engineers. He was awarded the 7th Sakurai Memorial Award in 1991, the Technical Paper Award by the IEICE in 1992, the Best Paper Award by the OEC in 1992 and 1994, the Ichimura Award in 1996, the R&D 100 Prize in 1997, the Development Award by I the IITE in 1999, and the Okochi Memorial Prize in 2000.

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