Single-peak femtosecond laser written cobalt-doped FBG for hot-wire anemometry

This study presents a hot-wire anemometer (HWA) using a multimode cobalt-doped fiber Bragg grating (MCDF-FBG) with a single reflection peak. A short FBG was inscribed into the MCDF using femtosecond laser direct writing technique to fabricate a temperature-sensing element. Dynamic thermal equilibrium between optical heating and airflow cooling was monitored by tracking shifts in the FBG's central wavelength using a high-power broadband light source in the C-band. The sensor sensitivity can be tuned by adjusting the MCDF length or broadband light source power. At a light source power of 505 mW, the anemometer achieves a maximum sensitivity of -6.432 nm/(m/s) at an airflow velocity of 0.1 m/s, with a measurement range of 0 to 5.5 m/s.