Plasmonic Fiber-Optic Photothermal Anemometers With Carbon Nanotube Coatings

Accurate measurement of wind speed is of crucial importance in the fields of scientific research,industrial production,wind power generation,and environmental monitoring.During recent decades,a large number of anemometers,based on different working principles including propeller,cup,ultrasonic,pressure plate,pressure tube and hot wire anemometers(HWAs),have been proposed and studied.Although these methods have been widely used,they still have shortcomings such as electromagnetic interference,and they cannot be used in micro-flow and corrosive environments.At the same time,the electrical methods which are commonly employed in the above examples may cause flammable gas explosions.As an alternative,fiber-optic wind speed sensing technology provides a method of all-optical measurement.Fiber-optic anemometers are gaining increasing attention due to their unique advantages,such as high precision,long-term stability,electromagnetic interference immunity,resistance to corrosive environments,and remote sensing capability.Among them,the hot wire anemometer(HWA)is a kind of important sensor that has been widely studied by measuring the cooling rate or temperature change of the sensor head when the sensor is heated to calculate the wind speed around the HWA.We propose and demonstrate an ultra-sensitive plasmonic fiber-optic hot-wire anemometer.This instrument comprises a highly-tilted fiber Bragg grating-assisted surface plasmon resonance(SPR)sensor which is coated with carbon nanotubes as the photothermal conversion medium.The carbon nanotubes on the sensor surface efficiently convert light from the heating laser,which is wavelength matched to the SPR window,into heat,thereby setting the sensor in an elevated temperature state.Air flow draws away surface heat,thus inducing a strong SPR wavelength shift and power modulation.Using this anemometer,we experimentally achieve a dynamic range of 0 to 0.65 m/s for wind speed measurement.Furthermore,we demonstrate real-time monitoring of wind speed by measuring the intensity of the heating laser.This sensor is simple and robust in structure.It has a wide range of potential applications in both scientific research and industrial production.