Arc Radius-Chirped Long-Period Fiber Grating by High Frequency CO₂-Laser Writing

A novel long-period fiber grating (LPFG) with arc grid having chirped radius is proposed and fabricated by CO₂-laser writing. The radius of arc grid in this LPFG is linearly chirped along the light transmission direction, which provides a gradually changed refractive index modulation (RIM) higher than that of conventional planar grid, and causes multiple spectral dips corresponding different coupling process. Two spectral dips of the radius-chirped LPFG shows opposite shifting directions to the same bending direction, but the same direction in the heating process. Due to the gap distance between the two oppositely shifted dips, the bending sensitivity reaches as high as 12.67 nm/m^-1, and the temperature effect can be self-compensated. This structure has potential to be applied in building, machine and ground monitoring.