Fabrication of long-period gratings in micro-structure specialty fiber with random holes in cladding

We demonstrated experimentally the fabrication of the long-period fiber gratings (LPFGs) in the micro-structure fiber under external tension with high repeatability by CO₂ laser. The micro-structure specialty fiber consists of a germania-doped core and a pure silica cladding with a nano-engineered ring that includes non-periodical nanometer-sized gas filled voids. The characteristics of grating growth were studied by using the dynamic analysis of laser writing process. It can be believed that the residual stress relaxation and frozen of the non-uniformed external stress account for the formation of LPFG.