CO2 laser writing of long period fiber grating in air-core photonic bandgap fiber as gas pressure sensor

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 by use of an improved CO2 laser system with an ultra-precision two-dimensional scanning technique, which produced single side periodic collapses in the micro-structured cladding of the air-core PBF. Such LPFG was utilized to measure the gas pressure with a sensitivity of −137 pm/MPa. A simulation model was built to study the gas pressure response mechanism of this kind LPFG. The stress distribution along the LPFG revealed that the outer gas pressure can lead to a stress concentration at the collapsed area and then transfer into the silica wall of the air-hole, which finally results in a shift of the resonant wavelength.