Overview of fiber sensor developments

Abstract

Prior to the early 1970s the main application for fiber optic waveguides had been for endoscopic instruments which are routinely used in medical procedures to’ look’ inside the human body. In devices of this type a bundle of optical fibers are arranged spatially such that when light from the object of interest is coupled into the endoscope, the resulting image emanating from the fiber bundle is spatially correlated with the object. The individual optical fibers used in these instruments are multimode with a relatively high optical loss. At about the same time there was a growing interest in the possibility of exploiting optics in communications systems as the potentially large bandwidth would allow significantly more simultaneous users over a single transceiver channel than the microwave links which were then being installed throughout the world. In order to achieve large bandwidth optical communications three elements are necessary:

• 1. an optical source ideally capable of direct modulation (amplitude, frequency or phase) at very high rates;

• 2. a very low loss guiding channel such as an optical fiber;

• 3. a high bandwidth optical detector.