"Microstructured Fiber Bragg Gratings" INVITED

The first fiber Bragg gratings were accidentally written in a Ge-doped silica fiber using a high power argon-ion laser [Hill et al. 1978]. Following this first evidence of photosensitivity in optical fibers, a huge effort was put into fiber gratings: improving their fabrication (they are now all externally inscribed), obtaining complex profiles, optimizing their performance, and incorporating them into devices and systems. On this line, the last decade was characterized by the birth of an emerging class of fiber gratings which can be defined as "microstructured fiber Bragg gratings." They refer to two main categories: one relies on short period gratings writing in microstructured optical fibers, whereas the second deals with standard short period gratings where structural defects at microscale are properly created within the hosting fiber by postprocessing techniques. This paper reviews the fabrication processes at the basis of this new technology as well as its properties and applications. Emphasis will be placed on principles of operation, technological developments and applications discussing perspectives, and challenges that lie ahead.