Channel-multiplexing for quasi-distributed acoustic sensing with orthogonal codes

With the increasing demands for large-scale acoustic sensing in many important fields such as hydrophone, vehicle tracking and pipeline monitoring, optical fiber-based distributed acoustic sensing (DAS) has experienced a rapid development. In recent years, quasi-distributed acoustic sensing (QDAS) based on single mode fiber with enhanced point array has emerged, which is a good approach to improve signal-to-noise ratio and deal with the interference-fading problem in DAS. However, similar to DAS, the performance of QDAS is also limited by the finite frequency domain resources. To break the trade-off between sensing bandwidth and distance, additional frequency domain resources are always needed to multiplex the sensing channel. Multiple-input multiple-output coding technology is an approach to realize QDAS channel-multiplexing with the orthogonal probe waves in the same frequency band. In this paper, the iteration constrain condition of the orthogonal codes is modified, and the generation method of more orthogonal codes with high and consistent suppression ratio for QDAS is provided. In the demonstration experiment, the QDAS has successfully achieved 5 times the sensing bandwidth expansion on a 5.19 km fiber based on 5 new orthogonal codes on the same frequency, with 5 m spatial resolution and 10 p epsilon/root Hz strain noise level. (C) 2021 Optical Society of America under the terms of the OSA Open Access Publishing Agreement