Multimode fiber, as a result of its large core diameter, has a relatively large number of modes that travel simulta-neously through the fiber. Each mode travels with its own group velocity and propagation constant, but interferes with other modes as they share the same medium. High-bandwidth and multi-point acoustic and vibration sensing is a critical asset for real-time condition monitoring, maintenance, and surveillance applications. In the case of large scales and harsh environments, optical fiber distributed sensing has emerged as a compelling alternative to. Wavelet transform can suppress the noise of multimode fiber optic micro-vibration sensing signal, but still seriously affected by the existing threshold function. In this paper, we proposed an improved wavelet threshold function based upon hyperbolic tangent function to perform wavelet denoising on. The purpose of this paper is to present a fiber-optic vibration sensor based on the monitoring of the mode distribution in a multimode optical fiber.
