Donald B. Keck
The "Information Age" is upon us. We generate, process, store, display, and transmit information in ever increasing amounts. Sensing and measuring is one aspect of information generation that will become an increasingly important activity in the coming years.
In the broadest context, the field of optical sensing includes both imaging and nonimaging sensors. The imaging category includes both proximity sensing and remote sensing; it encompasses all of the technology activity in charge-coupled device (CCD) focal plane arrays, for example. Imaging and remote sensing are each distinct fields in themselves and are beyond the scope of this study. This chapter focuses on the field of nonimaging sensor technology.
Work on nonimaging optical sensor technology began building momentum about a decade ago. Figure 6.1 shows the chronology of papers presented around the world in this broad area. Further examination of the publication data indicates that optical sensing involving fiber constitutes almost 93% of the work on nonimaging sensors. As a consequence, in benchmarking this technology it is important to examine activity in specialty fibers.
Breaking the work in fiber-optic sensor technology into even smaller subsets, one finds not only a very diverse field but a very fragmented marketplace as well. The myriad aspects of transmitting light through guiding structures results in multiple methods of sensing and measuring physical and chemical quantities; similarly, application of these techniques in the marketplace is found in many niches.
Fig. 6.1. Fiber-optic and optical sensor publication chronology (Dialog File 4, INSPEC Database).
Much of the optical sensor work is being done at universities and small companies; as a result, the current cost picture for most of the sensors being produced and studied is that of low-volume, high-cost manufacturing. Large companies are tending to watch and wait for emergence of a large application requiring their expertise in high-volume manufacturing before committing resources. All the benefits envisioned by workers in this field, and there are many, have not yet resulted in the scale-up required for low-cost, high-volume manufacturing. What is likely required is a convergence to a single technology platform where many sensor types can be produced from a relatively small number of component building blocks. While that concept is not new, and there seems to be a widely held view that the components of optical fiber communications can provide the necessary ingredients, to date that convergence has not happened, in North America, Asia, or Europe.