Optical fiber gratings written in microstructured optical fibers

Microstructured optical fibers are usually divided into two different types of fibers: solid-core Photonic crystal fibers (PCFs) and air-core photonic bandgaps fibers (PBGs). This paper presents the fabrication methods and applications of optical fiber gratings written in both solid-core PCFs and air-core PBGs. A sensitive stain sensor was demonstrated by use of a long period fiber gratings (LPFGs) written in solid-core PCFs. An in-fiber polarizer based on a LPFG is fabricated by use of a focused CO₂ laser beam to notch periodically on a PCF. A novel LPFG was written in air-core photonic bandgap fibers by use of a CO₂ laser periodically collapse air holes in the fiber cladding. Moreover, this paper also report fiber Bragg gratings written in small-core Ge-doped or pure-solid photonic crystal fibers with a two-beam interference technique employing an excimer or femtosecond laser.