Fiber Acoustic Sensor With Stable Operating-Point Based on a Photo-Thermal Cavity

Ambient temperature fluctuations inevitably affect the stability and accuracy of most of the existing fiber acoustic sensors. To overcome this drawback, a fiber acoustic wave transducer with stable operating-point based on a photo-thermal cavity (PTC) is proposed in this article. The proposed Fabry-Perot interferometer (FPI) is formed by splicing a Section of high-attenuation microfiber (HAMF) between a pair of wavelength-matched fiber Bragg gratings (FBGs). The applied acoustic wave would dynamically disturb the medium refractive index (RI) around the HAMF, causing the narrow Fabry-Perot interferometric fringe shift. The wavelength of the probe laser is tuned on the slope of the interferometric fringe. Theoretical analysis and experimental verification had been performed. The HAMF acts as an excellent active compensated component, which can steady the operating-point through adjusting the heating light source power. The proposed sensor structure has a compact size, simple fabrication and especially the stable operating-point, which make it more suitable for in-situ detecting in application of bioimaging or underwater sonar.