Cost-Effective Distributed Acoustic Sensing

Optical fibers are widely known in their ability to transfer huge amounts of data efficiently and cost-effectively. As the backbone of our communications networks, optical fibers are everywhere: underground or aerial in our streets, underwater in the oceans, along highways, railways, pipelines, power lines and fences, in campuses and in data centers. Optical fibers are by far the most used wired channel of communications and can be thought of as the nerve system of our vibrant sphere. It is considerably less known that the same optical fibers can be used as sensors. In Distributed Acoustic Sensing (DAS) a device called a ‘DAS interrogator’ is connected to one end of a telecom-type fiber and transforms it to a long array of ‘virtual’ microphones. By measuring and analyzing back-reflections from the fiber it detects acoustic signals at the vicinity of the fiber along its entire length. The technology enables not only detection of the acoustic signals but also determination of their position with spatial resolution of meters. We can think of DAS as a method for adding the huge optical nerve system of our world the functionality of sensing.  Today DAS is a commercial technology and many companies offer interrogators of various types for applications such as: intrusion detection, monitoring transportation, border defense, pipeline defense, seismic sensing and more. 

Current DAS interrogators are very expensive devices whose prices are in the dozens thousands of  dollars. As such they are mainly used for sensing in long linear sections of fiber and are considered unsuitable for short (~1km) and medium length (<10km) fibers. There is a need for affordable interrogators which will make the use of DAS in these cases cost-effective. Such interrogators will be suitable for installation in cities, campuses and infrastructure and in fibers deployed in tree topologies. With a short/medium range affordable DAS we will be able to sensitize numerous additional fibers in the sphere’s optical nerve system.  

The main components which determine the cost of DAS interrogators are the laser sources and the digitizers. DAS interrogators typically employ high end ultra-coherent lasers. Moreover, manufacturers often use more than one laser in a single interrogator for mitigating a phenomenon called ‘signal fading’ which causes various segments along the length of the fiber to become non-responsive. Most interrogators also comprise extremely fast digitizers with large memories. These components are needed for implementing the prevailing long range DAS. Our new patent pending approach for implementation of DAS aims for short and medium ranges. It is based on a broadband laser source and modest-performance digitizers. The innovative design compromises range for achieving a tremendous saving in the device Bill of Materials (BoM). It opens new market segments for DAS and renders millions of fiber branches DAS-accessible.   

Provisional patent application 

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