Investigation on acoustic wave transfer variation between fibers of different diameters and types using acoustic coupler

When using fiber Bragg grating (FBG) sensors in structural health monitoring (SHM) applications, one of the drawbacks is that the sensor location is fixed once it is installed and it is difficult to extend an already existing system. The use of an acoustic coupler to transfer fiber guided traveling waves from one fiber to another could resolve this issue as the system could be modified for extension. In this study, we investigate the coupling of optical fiber guided waves between two different types of fibers through an acoustic coupler. Specifically, input waves are launched into an input fiber and coupled to an output fiber through the acoustic coupler. The input waves are measured using a high-resolution 3D laser Doppler Vibrometer (LDV) and the output waves from the output fiber are measured using an FBG. We demonstrate that the wave coupling between two fibers varies with the cross-sectional area of the input fiber.