Gas Pressure Sensor Based on CO 2-Laser-Induced Long-Period Fiber Grating in Air-Core Photonic Bandgap Fiber

We reported a gas pressure sensor based on CO₂-laser-induced long-period fiber grating (LPFG) in an air-core photonic bandgap fiber (PBF). The LPFG was inscribed in an air-core PBF by the use of an improved CO₂ laser system with an ultraprecision 2-D scanning technique, which induced periodic collapses of air holes along the axis of the PBF. Such an LPFG could be used to develop a promising gas pressure sensor with a sensitivity of -137 pm/MPa. Moreover, a simplified fiber model with a relatively similar elastic response was developed to qualitatively study the gas pressure response of the LPFG inscribed in the air-core PBF. A simulated stress distribution along the LPFG revealed that the gas pressure leads to a stress concentration at the collapsed area of the air holes in the fiber cladding, which finally results in a resonant wavelength shift of the LPFG through an elastooptical effect.