Quasi-Distributed Fiber-Optic Acoustic Sensing With MIMO Technology

In the field of the Internet of Things, sensors with large-scale perception ability are urgently needed for the scenarios, such as structure health monitoring, vehicle tracking, and so on. Quasi-distributed acoustic sensing (QDAS), which uses a sensing fiber with an ultraweak reflector array to perceive thousands of points at the same time, shows great advantages in these applications. The sensing fiber integrates sensing and transmission functionalities together and is easy to be deployed on large-scale targets. With the development of QDAS, the performance limitations caused by the finite frequency-domain resource are gradually emerging. Multiplexing the frequency-domain resource can be the key to further performance breakthroughs. For this purpose, the multiple-input-multiple-output (MIMO) technology, which has been widely used in communication/radar systems, is introduced into QDAS in this article. The principles of QDAS with the MIMO technology are elaborated, and the feasibility is verified through simulations and experiments, in which the response bandwidth is tripled compared to the traditional single-pulse QDAS. To the best of our knowledge, this is the first time that the MIMO coding technology, i.e., orthogonal codes with the same frequency (OCSF), is used in QDAS. This work paves a new way for breaking QDAS performance limitations that are bounded by the finite frequency resource.