A novel flowmeter composed of a liquid crystal-filled nested capillary is proposed and experimentally demonstrated. Whispering gallery modes (WGMs) in the nested capillary are excited by a tapered fiber coupled perpendicularly to the nested capillary. The air flowing through the capillary cools it down, which leads to a temperature-induced change of the refractive index of the nematic liquid crystal (LC). This change in turn leads to a spectral shift of the WGM resonances, which can be linked to the airflow rate in the capillary. The temperature change in the LC was simulated considering the heat transfer between the LC and airflow in the capillary, which indicated that the LC temperature decreases in a nonlinear manner with the increase of the airflow rate. A flowmeter with the maximum sensitivity of 0.3423 nm·sccm-1 (nm/(mL·min-1 20 )) in the flowrate range from 0 to 2.52 sccm and a resolution of 5.72 pm was demonstrated in our experiment. The proposed sensor provides a new platform for WGM flowmeters and offers the advantages of good stability, competitive response time, high sensitivity, and miniature size.
|Accepted/In press - 13 Feb 2024