Efficient Fabrication of Compact Long-Period Gratings Using CO₂-Laser Splicer

We propose to inscribe a compact and reproducible long-period fiber grating (LPFG) in a standard single-mode fiber by a CO2-laser splicer that allows twisting the fiber stepwise during the laser heating process. The operation induced an azimuthal refractive index modulation, enabling the inscribed grating with asymmetric cladding modes coupling. By optimizing the parameters, the grating contrast with more than 30 dB was achieved with a 5.9 mm length. The approach could also fabricate ultra-LPFG, and the gratings with different diffraction orders are inscribed experimentally. The maximum twisting and strain sensitivities of the grating with
${LP}_{1,3}$
modes were achieved to be −0.09 nm/(rad/m) and −0.79 pm/
$\mu \varepsilon $
, respectively. The proposed method has not only overcome the limitation of laser spot size on grating fabrication by CO2-laser splicer but also has the advantage of flexible fabrication of the different grating structures for practical applications.