We present all-fiber resonating Fabry-Perot gas cells made with a piece of hollow-core photonic bandgap fiber (HCPBF) sandwiched by two single mode fibers with mirrored ends. A HC-PBF cavity made of 6.75-cm-long HC-1550-06 fiber achieved a cavity finesse of 128, corresponding to an effective optical path length of 5.5 m. Such HC-PBF cavities can be used as absorption cells for high sensitivity gas detection with fast response. Preliminary experiment with a 9.4-cm-long resonating gas cell with a finesse of 68 demonstrated a detection limit better than 7.5 p.p.m. acetylene.
We demonstrate an all-optical-fiber photoacoustic (PA) spectrometric gas sensor with a graphene nano-mechanical resonator as the acoustic detector. The acoustic detection is performed by a miniature ferrule-top nano-mechanical resonator with a ∼100-nm-thick, 2.5-mm-diameter multilayer graphene diaphragm. Experimental investigation showed that the performance of the PA gas sensor can be significantly enhanced by operating at the resonance of the grapheme diaphragm where a lower detection limit of 153 parts-per-billion (ppb) acetylene is achieved. The all-fiber PA sensor which is immune to electromagnetic interference and safe in explosive environments is ideally suited for real-world remote, space-limited applications and for multipoint detection in a multiplexed fiber optic sensor network.