In situ exploring the dynamic behaviors of gas bubbles in liquid by using a tapered dual-hole hollow fiber

Multiphase systems are often accompanied by highly complex gas-liquid-solid interactions and interface be-haviors, which are difficult to be captured directly. This work reports theoretically and experimentally the studies on monitoring the dynamic behaviors of the gas bubbles in liquid by using a tapered dual-hole optical fiber-based interferometer. As demonstrated by regulating their size, quantity, and arrangement, gas bubbles touching the waist region of the tapered fiber lead to a spectral response of the interferometer, and the total area of the gas-solid interface between them directly determines the wavelength shift of the output spectrum. Beyond that, the sensor with the uniform tapered waist region (length: 1.5 cm, diameter: CYRILLIC CAPITAL LETTER EF 5 mu m) is fabricated to explore the gas bubbles' coalescence. In this case, the gas bubbles contact each other until the waist region of tapered fiber is radially enclosed entirely. When the enclosed gas-solid interface area varies between 16,000 -24,000 mu m2, the wavelength shift responds exponentially to the area, and the sensitivity at the area of 16,000 mu m2 is calculated to be 2.42 pm/mu m2. The proposed sensing platform could be adapted to in situ and online explore the multiphase dynamics for applications such as cell analysis, energy production, and environmental monitoring.