CO2-laser writing of long period fiber grating in photonic crystal fiber by frozen-in viscoelasticity

Long period fiber gratings (LPFGs) formed in photonic crystal fibers (PCFs) are of considerable interest because they can provide many new opportunities for optical and biochemical sensing. LPFGs can be fabricated in PCFs by intense CO₂-laser radiation through deforming the fiber geometry or changing the glass structure. In this paper, we report a new, efficient way of writing LPFGs in PCFs, which is based on the generation of frozen-in inelastic tensile stresses in a tensioned PCF by CO₂-laser heating. The mechanism, known as frozen-in viscoelasticity, can also improve the writing efficiency of LPFGs in conventional single-mode fibers.