A UV-Cured Polymer/Aluminum-Microparticle Photothermal Encapsulated Liquid-Filled Fiber Mach-Zehnder Interferometric...

A high-sensitivity fiber-optic hot-wire anemometer based on a liquid-filled leaky-guided fiber Mach-Zehnder interferometer (LGFMZI) with UV-cured polymer/aluminum-microparticle photothermal encapsulation is proposed and experimentally demonstrated. The sensing element consists of a side-polished-fiber-assisted liquid-filled hollow-core fiber structure, in which a refractive-index-selected liquid core is introduced through a microslit to tailor the modal effective refractive-index difference and enlarge the free spectral range. The sensing region is uniformly encapsulated with a UV-cured NOA81 polymer layer containing aluminum microparticles. This encapsulation layer serves as both a photothermal conversion layer under 980 nm LD heating and a mechanical reinforcement layer. Under laser heating, the sensor is subsequently cooled by external airflow, converting wind-velocity variations into monotonic wavelength shifts. Experimental results show that, at an LD current of 80 mA corresponding to an optical power of 16 mW, the single-wavelength-dip sensor achieves a maximum airflow sensitivity of -22.922 nm/(m/s). The device also exhibits a fast transient response, with a rise time of 0.606 s and a fall time of 0.316 s. The proposed liquid-filled LGFMZI combines simple fabrication, photothermal encapsulation, high spectral readability, and stable airflow response, making it suitable for real-time fiber-optic hot-wire anemometry.