Fabrication and Mode Identification of Compact Long-Period Gratings Written by CO$_{2}$ Laser

We report highly compact (1.2 cm) long-period fiber gratings (LPGs) exhibiting strong grating effect (>30-dB loss) and low insertion loss (<0.25 dB) inscribed by a continuously scanned CO2 laser. The LPG resonances are also probed using traveling acoustic gratings with variable period. Our results show that these CO
₂
laser side-exposed LPGs predominantly couple to antisymmetrical cladding modes.