Review of long period fiber gratings written by CO2 laser

Abstract

This paper presents a systematic review of long period fiber gratings (LPFGs) written by the ${\text{CO}}_2$ laser irradiation technique. First, various fabrication techniques based on ${\text{CO}}_2$ laser irradiations are demonstrated to write LPFGs in different types of optical fibers such as conventional glass fibers, solid-core photonic crystal fibers, and air-core photonic bandgap fibers. Second, possible mechanisms, e.g., residual stress relaxation, glass structure changes, and physical deformation, of refractive index modulations in the ${\text{CO}}_2$ -laser-induced LPFGs are analyzed. Third, asymmetrical mode coupling, resulting from single-side laser irradiation, is discussed to understand unique optical properties of the ${\text{CO}}_2$ -laser-induced LPFGs. Fourthly, several pretreament and post-treatment techniques are proposed to enhance the efficiency of grating fabrications. Fifthly, sensing applications of the ${\text{CO}}_2$ -laser-induced LPFGs are investigated to develop various LPFG-based temperature, strain, bend, torsion, pressure, and biochemical sensors. Finally, communication applications of the ${\text{CO}}_2$ -laser-induced LPFGs are investigated to develop various LPFG-based band-rejection filters, gain equalizers, polarizers, and couplers.