Fabricating Air Pressure Sensors in Hollow-Core Fiber Using Femtosecond Laser Pulse.

In this paper, a hollow core fiber was spliced with standard single-mode fibers to form a fiber optic gas pressure sensor, and its sensing characteristics with single hole or multi-holes punched on the hollow core fiber with femtosecond laser pulses were investigated. The experiments demonstrate that the air pressure sensitivity of the single hole sensor was -3.548 nm/MPa, with a linearity of 99.45%, while its response times for air pressure's rise and fall were 4.25 s and 2.52 s, respectively. The air pressure sensitivity of the ten-hole sensor was up to -3.786 nm/MPa, with a linearity of 99.47%, while its response times for air pressure's rise and fall were 2.17 s and 1.30 s, respectively. Theoretical analysis and experimental results indicate that the pressure sensitivity of the sensor with an anti-resonant reflecting guidance mechanism mainly comes from the refractive index change of the air inside the hollow core fiber. The proposed device with multi-holes drilled by a femtosecond laser has the advantages of fabrication simplicity, low cost, fast response time, good structural robustness, high repeatability, high sensitivity to air pressure, and insensitivity to temperature (only 10.3 pm/°C), which makes it attractive for high pressure sensing applications in harsh environments.