High-sensitivity hot-wire anemometer using cobalt-doped fiber-based long-period gratings

A high-sensitivity hot-wire anemometer is proposed for use with a cobalt-doped fiber (CDF) based long-period grating (LPG) heated optically by a 1480 nm laser. The CDF-LPG absorbs laser power and generates heat inherently, thereby eliminating the need for both metal coating and mode coupling devices that are usually required in optical fiber grating anemometers. The dip wavelength of the CDF-LPG shifts with airflow velocity due to the cooling effect of the airflow. Airflow velocity is therefore measured by detecting the wavelength shift of the CDF-LPG. The measurement sensitivity is significantly enhanced by the high-temperature sensitivity of the LPG. In the experiment, high sensitivity up to -8.70 nm/(m/s) is achieved at an airflow velocity of 0.1 m/s, which is several times higher than that of fiber Bragg grating (FBG) based anemometers. The measurement range is 0-8.0 m/s. The response and recovery time are 0.4 and 0.3 seconds, respectively. The scheme of inscribing LPG on the CDF not only simplifies the production of hot-wire anemometers but also greatly improves the measurement sensitivity, making it a promising solution for high-precision airflow velocity measurement in practical applications.