Bioinspired Mode-Noise Suppressed Off-Axis Integrated Cavity for Rapid Dynamic Gas Detection

An innovative off-axis integrated cavity (OAIC) mimicking the tail flagellum of bacteria is proposed to solve the problems of mode interference noise and slow gas exchange caused by the nonuniform gas-flow field in traditional OAIC with large inside airflow fluctuation. The design concept of such a cavity, named bioinspired mode-noise suppressed OAIC, for the first time combines cavity-enhanced spectroscopy with bioinspired design to our knowledge. By redesigning the gas inlets into a pair of bioinspired tangential inlets, the original turbulent flow is transformed into a tangential rotating flow that guides fluid in a manner similar to bacterial flagella. Multiobjective optimization based on a genetic algorithm is used to optimize the bioinspired OAIC parameters, creating an orderly and uniform fluid within the cavity and reducing laser-gas interaction noise. The bioinspired OAIC shows no significant increase in concentration fluctuations within the 200-1500 sccm flow range, with optical mode-noise level reduced by 2.54 times at 800 sccm. The complete gas exchange time is shortened to 12 s. Allan deviation analysis revealed that the detection limit of bioinspired OAIC reached 34.4 parts-per-trillion (ppt) with an average time of 13.5 s. The bioinspired OAIC demonstrates long-term stability in continuous high-airflow gas detection owing to suppressed airflow fluctuation and minimized mode noise. The proposed bioinspired design concept can also be applied to the fabrication of other resonant cavities for fluid measurement.