We report an ultrasensitive gas refractive index (RI) sensor based on optical nanofiber couplers (ONCs). Theoretical analysis reveals that a dispersion turning point (DTP) exists when the diameter of the coupler is below 1000 nm. Leveraging this DTP, the gas RI sensitivity can be significantly improved to infinity. Then we experimentally demonstrate a DTP and achieve ultrahigh sensitivities of $\mathrm{46,470}\mathrm{nm}/\text{refractive}$ index unit (RIU) and $-45,550\mathrm{nm}/\mathrm{RIU}$ around the DTP using an ONC with a diameter of 700 nm. More importantly, the unique twin dips/peaks interference characteristics around the DTP offers further enhancement on the sensitivity to $92,020\mathrm{nm}/\mathrm{RIU}$. The demonstrated sensor not only shows vast potential in ultrasensitive pressure sensing, acoustic sensing, gas sensing, and gas phase biomarker detection, but also provides a new tool for nonlinear optics, ultrafast optics, quantum optics, and ultracold atom optics.

中文翻译：

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使用光学纳米纤维耦合器超灵敏地测量气体折射率

我们报告基于光学纳米纤维耦合器（ONCs）的超灵敏气体折射率（RI）传感器。理论分析表明，当耦合器直径小于1000 nm时，存在色散转折点（DTP）。利用此DTP，气体RI灵敏度可以显着提高到无穷大。然后，我们通过实验证明了DTP并实现了超高灵敏度$\mathrm{46,470}\mathrm{纳米}/\text{屈光的}$ 索引单位（RIU）和 $-45，550\mathrm{纳米}/\mathrm{IU}$使用直径为700 nm的ONC在DTP周围。更重要的是，DTP周围独特的双谷/峰干扰特性进一步提高了对DTP的灵敏度。$92，020\mathrm{纳米}/\mathrm{IU}$。演示的传感器不仅在超灵敏压力感测，声学感测，气体感测和气相生物标志物检测方面显示出巨大的潜力，而且还为非线性光学，超快光学，量子光学和超冷原子光学提供了新工具。