Novel Airflow Sensor Using Laser Heated Sn-Microsphere Airgap Fiber Fabry–Pérot Interferometer

We proposed a novel fiber optic hot-wire anemometer based on an Sn metal airgap fiber Fabry-Pérot interferometer (AG-FFPI). An airgap can be naturally formed between the fiber endface and melting Sn metal via overlaying technique. The metal Sn microcavity is directly heated by a 980 nm pumping laser diode (LD) to obtain desired steady-state high temperature (T) of the Sn metal, which exceeds T of the surroundings. Cooling effect on the heated Sn metal by air flowing is converted to optical wavelength blue shifted of interference fringes. Experimental results demonstrate that the proposed Sn metal microcavity AG-FFPI has good performance for airflow measurement and high response to T in the metal Sn. An average sensitivity of about 0.62 nm/(m/s) over the airflow range of 0-10 m/s is achieved with an Sn-microcavity of 9 μm and heated power of 45 mW.