Fiber optics represent a relatively new development in corrosion sensing/monitoring, with systems largely at the prototype, proof-of-concept stage. This technology resides in the broader domain of photonics (based on photons), which is increasingly displacing more conventional electronic devices (based on electrons). A lot has happened since the first drawn glass fibers in ancient Roman times and Claude Chappe's historic "optical telegraph" invention in France, dating back to 1790 (link to page by R. Victor Jones).

A fiber optic sensing system usually includes a sensor element, light transmitting path (fiber), light source, photodetector, signal processing and supplementary electronics.

Fundamental advantages of fiber optic corrosion sensing systems are related to:

• minimal risk of electromagnetic interference;
• high bandwidth;
• high sensitivity;
• small size - the analogy of a human hair and optical fibers is often used (hence favorable for embedding in smart structure applications);
• geometric versatility;
• high sensitivity;
• passive, in the sense of using dielectric materials.

Distinctions between fiber optic sensing systems have been made on the basis of intensity vs. interferometric sensing, physical vs. chemical sensing, extrinsic (the fiber acts as a transmission path) vs. intrinsic (the fiber itself acts as a sensor) and discrete (point) vs. distributed sensor systems. Prototype fiber optic corrosion monitoring systems have been based on concepts such as intensity changes of reflected light (surface reflectivity diminishing with corrosion product formation), color changes, detection of selected chemical species and strain changes (corrosion product build-up or corrosion "fuse" principles).