Design of highly-sensitive fiber thermal anemometer based on reflective photonic crystal fiber loop mirror

Abstract

• A reflective fiber loop mirror is firstly used in flow rate sensing. • The proposed sensor exists an infinite temperature-sensitivity point, which can be adjusted. • The fiber thermal anemometer has high sensitivity and long-distance sensing capability. A highly-sensitive fiber thermal anemometer was proposed and numerically designed based on reflective fiber loop mirror (RFLM). One ethanol-infiltrated birefringent photonic crystal fiber (BPCF) was imbedded in the RFLM as the sensing head, whose output interference spectrum was sensitive to surrounding temperature. Laser was used to heat the BPCF to a fixed temperature, but the temperature changed with the variation of surrounding flow rate. Therefore, the flow rate could be measured by monitoring the wavelength shift of the output spectrum. Through numerical analyses on the characteristics of the RFLM, the relationship between the flow rate and the temperature of the BPCF was numerical studied and then the structure parameters of the BPCF were optimized. Finally, numerical results showed that the maximum detectable flow rate could be enlarged to 20.8 m/s with the detection limit of 0.3 m/s, when the laser power was 100 mW. In addition, the defined quality parameter Q demonstrated that the sensitivity was improved to about 20 times.