Intensity-Interrogated Hot-Wire Anemometer Based on Narrow-Linewidth Laser and Cobalt-Doped Fiber Bragg Grating

An intensity-interrogated optical fiber hot-wire anemometer employing a cobalt-doped fiber (CDF) based fiber Bragg grating (FBG) is proposed. The CDF-FBG is heated and turned into a hot wire by using a high-power laser whose energy is absorbed by the CDF. In the presence of airflow, temperature of the CDF-FBG decreases with airflow velocity, causing wavelength blue-shift of the CDF-FBG. A narrow-linewidth laser with the emission wavelength located well at the slope of the reflection spectrum of the CDF-FBG is used to detect the airflow velocity through the measured reflected optical power from the CDF-FBG. Airflow velocity measurement is achieved with sensitivity of
$\mathbf{321.46}\ \boldsymbol{\mu} \mathbf{W}/(\mathbf{m}/\mathbf{s})$
and the measurement range of 0-0.2 m/s.