The end of the last century and the beginning of the present one have been labeled as the “information era.” When speaking about information technology, one’s first thought goes to Internet, ubiquitous portable PCs, and mobile phones (in other words, microelectronics), and one tends to forget the substantial fact that a major portion of the information that a person receives is still optical. Optical information may arrive to our eyes directly from the “natural” surrounding environment or from an “artificial” medium (a newspaper, a TV screen, a computer monitor, the display of a mobile phone). Technical progress has allowed us to obtain optical information not only from our close-by environment, but also from materials and locations that are distant either on a macroscopic distance scale (by using astronomical telescopes) or on a nanometric scale (by using the most modern microscopy tools). The same progress, moreover, has allowed us to get increasingly more detailed (and quantitative!) information on the physical, chemical, and biological properties of our environment. It is in this way that optical metrology and sensing has developed as a broad interdisciplinary field that keeps growing at a fast rate, both in its fundamental aspects and in its relative technological developments and application areas.
Most of the recent tremendous advances in the development and use of new optical sensors and instruments have been made possible mainly by the availability of two classes of components/devices: (1) laser sources with increasingly better characteristics, and in a broader wavelength interval; and (2) guided-wave optics (namely, optical fibers and integrated optical circuits). This chapter aims to give a brief overview of developments and perspectives in the latter area. Indeed, this is not an easy task, because the rate of growth involved has been (and still is) very rapid, and the number of books and papers published on this subject is overwhelming.
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