DETECTION OF VIBRATION FREQUENCY BASED ON NO CORE FIBER

Vibration detection is an important feature in machinery health monitoring, in which used to detect faults and damages in heavy machines. This work demonstrated a fiber vibration sensor based on SingleMode-No Core-SingleMode (SNCS) fiber structure for low frequency vibration detection. When light coupled from Single-Mode-Fiber (SMF) to No-Core-Fiber (NCF), high-order Eigennodes will be excited and caused interference between different modes occurred along NCF. Different vibration frequencies change the interference pattern inside the NCF as NCF acts as multimode waveguide. Two sets of SNCS sensor with different length of 1.65cm and 2.85cm obtained an average Electric Field Norm (EFN) losses of 5.242% and 9.233% respectively. The SNCS sensor was proven to be capable in detecting vibration frequencies ranging 100Hz to 3000Hz with vibration intensity of 3V and 5V. The maximum relative error of the vibration frequency is %. The SNCS structure has the advantage of easy to fabricate, low cost and immune to electromagnetic interference, which can be used in critical environment.