Over the past 20 years two major product revolutions have taken place due to the growth of the optoelectronics and fiber optic communications industries. The optoelectronics industry has brought about such products as compact disc players, laser printers, bar code scanners, and laser pointers. The fiber optic communications industry has literally revolutionized the telecommunications industry by providing higher-performance, more reliable telecommunication links with ever-decreasing bandwidth cost. This revolution is bringing about the benefits of high-volume production to component users and a true information superhighway built of glass. In parallel with these developments, fiber optic sensor technology has been a major user of technology associated with the optoelectronic and fiber optic communications industry. Many of the components associated with these industries were often developed for fiber optic sensor applications.

Fiber optic sensor technology, in turn, has often been driven by the development and subsequent mass production of components to support these industries. As component prices have fallen and quality improvements have been made, the ability of fiber optic sensors to displace traditional sensors for rotation, acceleration, electric and magnetic field measurement, temperature, pressure, acoustics, vibration, linear and angular position, strain, humidity, viscosity, chemical measurements, and a host of other sensor applications has been enhanced. In the early days of fiber optic sensor technology, most commercially successful fiber optic sensors were squarely targeted at markets where existing sensor technology was marginal or in many cases nonexistent. The inherent advantages of fiber optic sensors, which include

1. their ability to be lightweight, of very small size, passive, low-power, resistant to electromagnetic interference,

2. their high sensitivity,

3. their bandwidth, and

4. their environmental ruggedness, were heavily used to offset their major disadvantages of high cost and end-user unfamiliarity.

The situation is changing. Laser diodes that cost $3000 in 1979 with lifetimes measured in hours now sell for a few dollars in small quantities, have reliability of tens of thousands of hours, and are widely used in compact disc players, laser printers, laser pointers, and bar code readers. Single-mode optical fiber that cost $20=m in 1979 now costs less than $0.10=m, with vastly improved optical and mechanical properties. Integrated optical devices that were not available in usable form at that time are now commonly used to support production models of fiber optic gyros. Also, they could drop in price dramatically in the future while offering ever more sophisticated optical circuits. As these trends continue, the opportunities for fiber optic sensor designers to product competitive products will increase and the technology can be expected to assume an ever more prominent position in the sensor marketplace. In the following sections the basic types of fiber optic sensors being developed are briefly reviewed followed by a discussion of how these sensors are and will be applied.