Evanescent wave fiber optic sensor based on SnO2/MoS2 composite material and its dual-parameter response characteristics to NO2 and humidity

An NO 2 fiber-optic sensor with integrated humidity compensation functionality was proposed. • Excellent NO 2 detection performance with a detection limit as low as 10 ppb. • SnO 2 /MoS 2 composite significantly enhances sensitivity. This study proposes an evanescent wave fiber-optic sensor based on an SMF-CLF-TCF-CLF-SMF interferometric structure and a SnO 2 /MoS 2 composite sensitive film, which responds to NO 2 concentration and environmental humidity through changes in transmitted light intensity and interference wavelength shift, respectively, exhibiting dual-parameter differential spectral response characteristics. The structure utilizes a coreless fiber for mode conversion and employs a Thin-core Fiber as the region for evanescent field excitation and sensitive material coating. SnO 2 and MoS 2 nanomaterials were synthesized via hydrothermal methods, and SnO 2 /MoS 2 composites with varying MoS 2 loading ratios were prepared using ultrasonic mixing. Under conditions of 25 ℃ and 20% RH, the SnO 2 /1.0 wt% MoS 2 sensor demonstrated optimal overall NO 2 sensing performance: achieving a sensitivity of 2.26 dB/dec over the 10–5000 ppb range—approximately 9 times higher than that of pure SnO 2 sensors—with a minimum detectable concentration of 10 ppb, response and recovery times of approximately 16 s and 12 s, respectively, and excellent long-term stability. Humidity experiments were independently conducted at 25 ℃; as relative humidity increased from 20% to 80%, the interference spectrum continuously shifted toward shorter wavelengths, reaching a maximum wavelength shift of 16.45 nm. Experimental results indicate that changes in NO 2 concentration primarily manifest as variations in transmitted light intensity, whereas humidity changes mainly result in shifts in the interference wavelength. This research provides an experimental foundation for high-sensitivity, ppb-level NO 2 fiber-optic detection at room temperature and dual-parameter sensing of both NO 2 and humidity. Download: Download high-res image (179KB) Download: Download full-size image