DISTRIBUTED ACOUSTIC SENSING SYSTEMS AND METHODS EMPLOYING UNDER-FILLED MULTI-MODE OPTICAL FIBER

摘要

An illustrative distributed acoustic sensing system includes a multi-mode optical fiber cable for distributed sensing and a distributed acoustic sensing interrogator coupled to the multi-mode optical fiber cable via a single mode optical fiber. The interrogator derives distributed acoustic measurements from Rayleigh backscattering light that is initiated with a substantially under-filled launch configuration that is designed to excite only the lowest-order modes of the multi-mode optical fiber. Mode conversion within the multi-mode optical fiber is anticipated to be negligible. For elastic scattering (i.e., Rayleigh scattering), it is further anticipated that the scattered light will be primarily returned in the incident propagation mode, thereby escaping the extraordinarily large coupling loss that would otherwise be expected from coupling a single-mode optical fiber to a multi-mode optical fiber for distributed sensing. Experiments with graded index multi-mode optical fiber have yielded positive results.

主权项

1. A distributed sensing system that comprises:
a multi-mode optical fiber cable deployed for distributed sensing; and a distributed acoustic sensing interrogator having a single-mode optical fiber that communicates light from a single transverse mode laser source; and a mode field adapter that couples the light from the single-mode optical fiber to the multi-mode optical fiber cable, wherein the distributed acoustic sensing interrogator derives distributed acoustic measurements from Rayleigh backscattered light received from the multi-mode optical fiber cable.