Optical Fiber Photoacoustic Gas Sensor With Graphene Nano-Mechanical Resonator as the Acoustic Detector

We report an all-optical fiber photoacoustic gas sensor with a graphene nano-mechanical resonator as the acoustic detector. The acoustic detector is a Fabry-Perot interferometer formed by attaching a 100-nm-thick, 2.5-mm-diameter multilayer graphene diaphragm to a hollow cavity at the end of a single-mode optical fiber. By operating at one of the mechanical resonances of the diaphragm, the sensitivity for acoustic detection is enhanced and a noise equivalent minimum detectable pressure of 2.11 μPa/Hz^1/2 at 10.1 kHz is demonstrated. Detection of acetylene gas is demonstrated with a distributed feedback semiconductor laser tuned to the P(9) absorption line of acetylene and a lower detection limit of 119.8 parts-per-billion (ppb) is achieved with 123.9-mW pump power. Theoretical analysis shows that by increasing the Q-factor of the resonator, which may be achieved by operating at low gas pressures, ppb level gas detection is possible. The all-fiber photoacoustic gas sensor is immune to electromagnetic interference, safe in flammable and explosive environment, and would be ideally suited for remote, space-limited applications and for multipoint detection in a multiplexed fiber optic sensor network.