Long Period Fiber Gratings Written in Photonic Crystal Fibers by Use of CO₂ Laser

Photonic crystal fibers are usually divided into two different types of fibers: solid-core photonic crystal fibers (PCFs) and air-core photonic bandgaps fibers (PBFs). We presented the fabrication methods and applications of long period fiber gratings (LPFGs) written in these two types of photonic crystal fibers by use of a CO₂ laser. A stain sensor with a high sensitivity was demonstrated by use of an LPFG written in solid-core PCFs. An in-fiber polarizer based on an LPFG was fabricated by use of a focused CO₂ laser beam to notch periodically on a PCF. A novel LPFG was written in an air-core PBF by use of a CO₂ laser to collapse periodically air holes in the fiber cladding.