Thermal optical fiber sensor based on GaAs film for fluid velocity measurement

A thermal optical fiber sensor based on laser-heated GaAs film has been proposed and demonstrated in this work. The principle of the sensor is based on the hot-wire effect, i.e., the convective heat loss from the laser-heated GaAs film to the fluid. An 810 nm fiber laser is used to heat the GaAs film due to its excellent opto-thermal effect. Due to the intrinsic thermal optical property of GaAs that the transmission spectrum shifts with temperature, the temperature change introduced by the flow can be demodulated by the spectral shifts of the reflection spectrum. The sensing principle and performance have been studied by numerical simulation based on finite element analysis and have been verified by experiment. The maximum flow velocity sensitivity can reach 0.453 nm/(cm/s) over a broad range from 0.85-59 cm/s. The resolution is 0.5 cm/s, based on the wavelength resolution of 1.1 nm. Moreover, the micron-scale fiber sensor has good robustness, and the heating medium is also biologically compatible. Given its capability, compactness, and biocompatibility, the proposed flow velocity fiber sensor has a high application potential in invasive blood flow measurement.