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 CO2 laser irradiation technique. First, various fabrication techniques based on CO2 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 CO2-laser-induced LPFGs are analyzed. Third, asymmetrical mode coupling, resulting from single-side laser irradiation, is discussed to understand unique optical properties of the CO2-laser-induced LPFGs. Fourthly, several pretreament and post-treatment techniques are proposed to enhance the efficiency of grating fabrications. Fifthly, sensing applications of the CO2-laser-induced LPFGs are investigated to develop various LPFG-based temperature, strain, bend, torsion, pressure, and biochemical sensors. Finally, communication applications of the CO2-laser-induced LPFGs are investigated to develop various LPFG-based band-rejection filters, gain equalizers, polarizers, and couplers.

Long Period Gratings in New Generation Optical Fibers

“…Besides, Wang et al believe that for the LPG written in HC-PCF, periodic perturbations of the waveguide (geometric) structure could be the dominant factor that causes resonant mode coupling, although the stress relaxation-induced index variation may also contribute a little (Y. Wang et al, 2008Wang et al, , 2010. Recently, the same group theoretically investigated the LPGs fabricated in HC-PCFs with a pulsed CO 2 laser .…”

“…Both methods, to obtain the localized heating of the fiber, rely on a point-by-point writing approach and therefore they inherit the advantageous flexibility already mentioned. Also for these techniques there are several mechanisms that contribute to the refractive index modulation: relaxation of frozen stresses during fiber drawing, physical deformation, glass compaction or expansion, core dopants diffusion, among which the predominant cause depends on the heating treatment, the fiber type and any mechanical stress applied (Rego et al, 2005a;Y. Wang, 2010).…”

“…This particular feature, indeed, has a number of advantages such as lower Rayleigh scattering, reduced nonlinearity, novel dispersion characteristics, and potentially lower loss compared to conventional optical fibers. Fabrication of gratings in PCFs fiber still represents a challenge for the scientific community (Cusano et al, 2009;Y. Wang, 2010).…”

Temperature sensing using an optical time domain reflectometer and mechanical long-period fiber gratings fabricated from a heat-shrinkable tube

“…Numerous techniques are available for fabricating LPFGs. Approaches that have been demonstrated include periodic local heating of the fiber using a CO/CO 2 laser [4,5] or electric arc discharge [6,7]. Fabrication techniques for mechanically induced LPFGs have also been reported [8, 9, 10].…”

Analysis of transmission characteristics of tilted long period fiber gratings with full vector complex coupled mode theory?

“…Correspondingly, many investigations are made on them [7][8][9][10][11][12][13]. Recently, the titled fiber gratings, especially the tilted fiber Bragg gratings (TFBGs) with the small grating period have attracted tremendous attention due to their applications in the sensing area [14][15][16][17][18][19][20][21][22].…”