Intensity-Interrogated Hot-Wire Anemometer Based on Cobalt-Doped Fiber Bragg Grating

An intensity-interrogated optical fiber hot-wire anemometer employing a cobalt-doped fiber Bragg grating (CD-FBG) is proposed and experimentally demonstrated. The CD-FBG absorbs light energy from a 1480 nm laser and turns into a “hot wire” with its temperature decreasing and therefore reflection spectrum blue-shifting with the airflow velocity. To achieve intensity interrogation, a wavelength-switchable narrow-linewidth probe laser is used, which makes the reflected optical power from the CD-FBG change monotonously with the airflow velocity in a certain measurement range. In the experiment, the high sensitivity of −1248 μW/(m/s) is achieved at the airflow velocity of 0.05 m/s. The measurement range is extended to 0 m/s–8.0 m/s by switching the probe laser wavelength. The response time and recovery time of the anemometer are 0.5 seconds and 0.6 seconds, respectively. The intensity interrogation scheme and simple structure of the anemometer probe greatly reduce the cost and make it a promising solution for high-precision airflow velocity measurement in many practical applications.