Hollow-Core Fiber-Based High Finesse Resonating Cavity for High Sensitivity Gas Detection

High finesse hollow-core photonic bandgap fiber (HC-PBF) resonating Fabry-Perot gas cells are presented. These gas cells are made with a piece of HC-PBF sandwiched by two single mode fibers with mirrored ends. A HC-PBF cavity made with 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. Experiment with a 9.4-cm-long Fabry-Perot gas cell with a finesse of 68 demonstrated a detection limit of 7 ppm acetylene. Compared with a single-path nonresonating HC-PBF, the use of a high finesse resonating HC-PBF cavity can reduce significantly the effect of modal interference on gas detection and improve the detection sensitivity. The cavity-enhanced HC-PBF gas cells enable stronger light-gas interaction and can be used to develop all-fiber gas sensors with high sensitivity and fast response.