Fabrication and Analysis of a Gas Sensor Utilizing a Fabry–Perot Interferometer With Varied Thicknesses of ZIF-8 Coating on End-Faced Single-Mode Optical Fiber

This article investigates the potential of integrating optical fiber (OF) and sensitive thin film coating materials to develop diverse chemical sensing platforms. We utilized a layer-by-layer synthesis technique, along with specific pre-post-treatment methods, to create highly effective nonporous metal-organic frameworks (MOFs), specifically zeolitic imidazolate framework (ZIF)-8, ranging from the nanometer scale to the micrometer scale (800 nm to $110 ~\mu \text{m}$ ). Additionally, we successfully cultivated ZIF-8 on both sides of a single-mode fiber (SMF) with thicknesses of 25 and $50 ~\mu \text{m}$ . In a separate experiment, we successfully grew ZIF-8 on one side of an OF, achieving a thickness of $10 ~\mu \text{m}$ . The sensor demonstrated notable sensitivity to ethanol, with the fringe valley shifting from 1602 to 1606.8 nm as the ethanol concentration increased from 30 to 70 ppm. Reducing the thickness of the MOF coating led to notable improvement in response and recovery times. Specifically, for a $10 ~\mu \text{m}$ cavity length, response time decreased to around 17 s and recovery time to 50 s, compared to $110 ~\mu \text{m}$ cavities which took 1 min to respond and 4 min to recover at room temperature.