High-sensitivity fiber-tip liquid level sensor with welded AuSn nano-film

We proposed a novel method for preparing nanoscale hermetic composite films using AuSn alloy to fabricate a fiber-optic Fabry-Pérot interferometer, developing a liquid-level sensor. The sensor employs a ceramic ferrule integrated fiber-tip with an AuSn alloy composite film, exhibiting high sensitivity for liquid-level measurement and repeatable response for long-term underwater applications. As a result, the sensor's liquid-level sensitivity is measured to ∼260 pm/cm, with a liquid-level resolution of ∼0.01 cm and a liquid-level measurement range of ∼403 cm. The proposed sensor demonstrates significant potential for underwater multi-parameter sensing applications, attributed to its high sensitivity and excellent stability.