Dual-sagnac optical fiber sensor used in acoustic emission source location

Based on all-fiber single-Sagnac interferometer (SI) technology, a dual-Sagnac optical fiber sensor is introduced to locate the acoustic emission(AE) source. It consists of two Sagnac interferometeres each with a delay loop constituting a symmetric superposition. So it is nonreciprocal and the two SIs work independently to measure the position of the AE source along fiber. A fast Fourier transform(FFT) is performed on temporal response to extract its power spectrum where null frequencies occur. With null frequency method, the location has been implemented by experiment. Besides, study on the influence of different sensing unit and the overall fiber length on accuracy have been carried out separately for future optimization. The theoretical analysis and experimental results show that the dual-Sagnac optical fiber sensor is feasible for AE source location and the accuracy increased compared with single SI. The dual-Sagnac optical fiber sensor is potential for the structural integrity monitoring and nondestructive testing(NDT) applications.