Optical Characteristics of Fiberoptic Evanescent Wave Sensors

Abstract

The availability of low-loss optical fibers with the associated benefits of freedom from electromagnetic interference, small size, light weight, and wide bandwidth has led to the development of sensors, both intrinsic and extrinsic. Commercial offerings of the extrinsic type, in which the sensing element is attached to the end of the fiber, are becoming readily available for the measurement of many physical and chemical parameters, e.g., temperature, pressure, and pH. The intrinsic sensors, in which the optical fiber itself functions as the sensor, potentially offer more sensitivity and versatility. In some cases, distance or location information may be obtained with intrinsic sensors by means of optical-pulse techniques. The intrinsic sensors are usually more complex in their instrumentation or environmental requirements, and their entry into the commercial market has proceeded more slowly.