Post-treatment techniques for enhancing mode-coupling in long period fiber gratings induced by CO 2 laser

Two promising post-treatment techniques, i.e. applying tensile strain and rising temperature, are demonstrated to enhance the mode-coupling efficiency of the CO 2 -laser-induced long period fiber gratings (LPFGs) with periodic grooves. Such two post-treatment techniques can be used to enhance the resonant attenuation of the grating to achieve a LPFG-based filter with an extremely large attenuation and to tailor the transmission spectrum of the CO 2 -laser-induced LPFG after grating fabrication.