Optical-Fiber Sensors
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Optical-Fiber Sensors G.F. Fernando, D.J. Webb, and Pierre Ferdinand, Guest Editors Abstract The primary aim of this issue of MRS Bulletin is to present an overview of the deployment of optical-fiber sensors in a selected range of applications. The topics covered include a general introduction to optical fibers; a review of the sensing mechanisms that are available to monitor strain, temperature, pressure, chemical species, damage, and acoustic emission; and the use of optical-fiber sensors in medical applications. This introductory article presents a brief discussion of the advantages and disadvantages of optical-fiber sensors. Keywords: optical-fiber sensors, optical materials, optoelectronic materials.
Advantages and Issues in the Use of Optical-Fiber Sensor Systems Advantages The current market for optical-fiber-based sensor systems has been reported to be in the region of $550 million.1 The global market for sensors is expected to reach more than $50 billion by 2008.2 The tremendous interest and activity in opticalfiber sensors (OFSs) may be attributed to one or more of the following reasons: 1. A wide range of optical fibers exhibiting low attenuation over a large wavelength
range are currently available, along with a wide selection of the associated light sources, detectors, and optical components. Fibers can be selected to suit specific applications and operating temperatures (see Table I). 2. The relatively small dimensions and uniform cross sections of optical fibers make surface-mounting them or embedding them into materials easy. In general, when embedded, they tend not to influence the quasi-static tensile mechanical properties of materials.
3. They are immune to electromagnetic interference and therefore can be deployed in areas where electrical-based sensors would fail or require expensive protection. They can also be deployed in harsh (hightemperature) and hostile (chemically reactive) environments. 4. OFSs can be used to monitor a wide range of parameters including strain, temperature, pressure, humidity, vibration, specified chemicals (e.g., to gauge aging or degradation), acoustic emission, and fracture. Although a number of these sensor systems have been demonstrated successfully in the laboratory under ideal conditions, their performance when exposed to the rigors of on-site applications is only now being given greater emphasis. A summary of selected parameters and the associated sensing mechanisms is presented in Table II. 5. The options of remote data telemetry over kilometers without corruption from electromagnetic interference and on-line data acquisition are an extremely attractive feature of OFSs. 6. Unlike conventional electrical-based sensors, OFSs can be multiplexed. In other words, a number of similar or different sensors can be attached along a single optical fiber. With certain sensor designs, distributed sensing can also be achieved along the length of a fiber.
Issues OFSs have their limitations, and these need to be appreciated if their advantages
Table I: Selected Properties
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