Ironically, many of the passive components used extensively in telecommunications systems today were developed originally for fiber optic sensor systems. While the commercial sensor applications have developed more slowly, the breadth and scope of such applications continue to push the design engineer to develop new components. These developments have included, for example, splitters using hard clad silica fiber for medical and environmental sensors, improved splitters using polarization preserving fiber for gyroscopes, and unique wavelength division multiplexers for medical sensors. This paper will review the state of the art of passive fiber optic components with particular emphasis on sensor applications.
Optimisation of optical fibre design to fully realise the potential of optical sensing systems is discussed. In particular, waveguide geometry and host glass composition are discussed with reference to specific sensor applications.
Progress in the development of fiber sensors with the Fabry-Perot interferometer (etalon) configuration is reviewed. Fabrication methods and performance results for intrinsic and extrinsic sensors are presented. Application of these devices in measuring temperature, strain, ultrasonic pressure, and gas pressure in internal combustion engines is described. Techniques by which the fiber Fabry-Perot sensors have been successfully embedded in composites and metals are indicated.
Micromachined sensors, especially those based upon silicon technology are compatible with simple batch processing and so, in principle, may be fabricated repeatably and economically. For relatively precise (=0.1% and better) measurements, microresonators in which the measurand is caused to modulate the resonant frequency of a mechanical structure can be particularly attractive. Micromechanics enables these resonators to be readily fabricated to the appropriate sub-millimetre dimensions which are compatible with all optical excitation and detection of the resonance phenomena. The ability to transmit the necessary optical signals along fibres results in a precise miniature and potentially rugged transducer system. These fibre optic resonator devices which are entirely electronically passive are particularly suited to applications involving environments subject to high electro-magnetic fields and/or to extremes of temperature.
This paper introduces the concepts underpinning the realisation of micromachined resonator fibre optic sensors, discusses the achievements in prototype sensor systems realised to date and projects the future requirements which must be fulfilled before the technology can realise its full commercial potential. Measurements to 0.1% accuracy over very wide temperature ranges have been demonstrated to be feasible and applications in the difficult environments typified by aerospace, industrial, and automotive measurements and in chemical/biochemical systems are emerging.
Since the initial demonstrations of various fiber optic sensing techniques in the laboratory, much progress has been made in creating practical sensors for use in real world applications. In particular, sensors utilizing the properties of optical gratings and sensors exploiting polarization effects have been intensively investigated. Both multimode and single mode fiber sensors have utilized these transduction techniques. In this paper, a brief review of grating and polarization optics will be provided followed by a more detailed analysis of a number of specific multimode and single mode fiber optic sensors. Included among these will be hydrophones, pressure sensors, strain sensors, vibration sensors, linear position sensors and speed/torque sensors. The practical application of these sensors will also be discussed.
This paper reviews the technical evolution of the interferometric fiber-optic gyroscope, or l-FOG, over the last fifteen years. Today a psychological barrier has been passed, and it is now accepted that this new technology will find many applications during the 90's.
A critical review of the developments in the resonator fiber optic rotation sensor technology is presented. Error terms and proposed solutions are discussed. Supporting experimental results and their significance are summarized.
This critical review paper covers the field of distributed optical fiber sensors, where measurements may be taken along the length of a continuous section of optical fiber. Such a feature greatly increases the information that can be obtained from a single instrument and hence the cost per sensing point can be more acceptable.
The review will not attempt to cover all methods, but will give a selection of some of the more interesting theoretical concepts, describe the current status of research and indicate where optical sensing methods are being applied in commercial instruments.
Considerable progress has been made in the use of fiber optic magnetic sensors in actual field environments, especially for undersea applications. This paper reviews the results of three fiber magnetometer systems: 1) a heading sensor for undersea towed array applications; 2) a remote ac magnetometer designed for land use; and 3) a magnetometer array for undersea magnetic measurements. In each case, relevant design parameters, laboratory test results, and, where applicable, field test results are presented.
The revolutions in the fiber optic telecommunication and optoelectronic industries have enabled the development of fiber optic sensors that offer a series of advantages over conventional electrical sensors. This development in combination with advances in composite material technology have opened up the new field of fiber optic smart structures that offers mechanical and structural engineers the possibility of incorporating fiber optic nervous systems into their designs.
Progress continues in the development of fiber optic sensors in industry. Most applications still appear to be in special niche areas, and characterized by a relatively small number of units sold. Signs are present, however, that indicate this situation may be changing. This presentation will include specific examples of recent development work and fiber optic sensor hardware used in applications such as manufacturing, power generation, and chemical processing. An assessment will be made of sensor performance in present applications, and progress made over the last several years in matching the technology and capability of fiber optic sensors to industrial needs. Both the shortcomings and advantages of fiber optic sensors will be discussed along with the outlook for future new applications, the direction fiber sensor technology is going, and why.