Multimode Fiber Vibration Sensing via Spatial Mode Filtering
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Solution Overview
Problem
Current systems cannot simultaneously use Coherent Rayleigh noise (CRN) and Distributed Temperature Sensing (DTS) due to the requirement for single-mode fibers for CRN, which degrades DTS performance, and the impracticality of installing separate fibers for both technologies, especially in existing multimode fiber installations.
Innovation Solution
An OTDR system utilizing a multimode sensing optical fiber with a single spatial mode filtering system to detect Rayleigh backscattered light, allowing for CRN measurements while maintaining DTS performance by selecting a single speckle from the returned backscatter, thereby enabling the use of existing multimode fiber infrastructure for both CRN and DTS applications.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If single-mode fiber is used for CRN measurements, then measurement precision is improved, but DTS performance deteriorates
Solution Approach 1:
The patent segments the spatial modes within the multimode fiber and selects only a single spatial mode for CRN detection. This segmentation allows the system to achieve single-mode-like measurement precision for CRN while utilizing the multimode fiber's capability for DTS, thereby resolving the contradiction between CRN precision and DTS performance.
Solution Approach 2:
The patent applies local quality by creating a spatial filter that selectively processes only a specific spatial mode of the backscattered light. This local processing ensures high contrast for CRN measurements in the selected spatial mode while preserving the overall multimode fiber structure needed for DTS applications.
2Measurement precision
If separate fibers are installed for DTS and CRN, then measurement precision for both is maintained, but device complexity increases
Solution Approach 1:
The patent makes the multimode fiber universal by enabling it to perform both DTS and CRN measurement functions simultaneously. Through spatial mode filtering, the same fiber infrastructure supports both measurement types, eliminating the need for separate fibers and reducing overall system complexity while maintaining measurement precision for both applications.
Solution Approach 2:
The patent merges the DTS and CRN measurement capabilities into a single multimode fiber system. By combining both measurement functions in one fiber with appropriate spatial filtering, the system reduces installation complexity and device complexity while preserving the measurement precision of both techniques.
3Device complexity
If multimode fiber is used for CRN measurements, then device complexity is reduced, but measurement precision deteriorates
Solution Approach 1:
The patent segments the multiple spatial modes in the multimode fiber and isolates a single spatial mode for CRN detection. This segmentation restores the high contrast necessary for precise CRN measurements while retaining the simplicity of using multimode fiber infrastructure, thereby achieving both reduced device complexity and maintained measurement precision.
Solution Approach 2:
The patent introduces a spatial filter as an intermediary component that processes the multimode backscattered light to extract a single spatial mode. This intermediary enables CRN measurements with high precision using multimode fiber, bridging the gap between the simplicity of multimode installation and the precision traditionally requiring single-mode fiber.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables the detection of disturbances in elongate structures using existing multimode fiber installations, enhancing the capability to detect vibrations and temperature changes, and refining DTS data by providing high contrast coherent backscatter signals, thus facilitating early detection of potential cable failures and other disturbances.
Implementation Method 1
detect Rayleigh backscattered light produced by the multimode sensing optical fiber in response to the pulse of light
Data Source
AI summary
An optical time domain reflectometry (OTDR) system is configured to detect Rayleigh backscatter reflected from a multimode sensing optical fiber. The system includes a single spatial mode filtering system to select a single speckle of the Rayleigh backscatter produced in response to an optical pulse launched into the multimode fiber. The detected single speckle may be used for distributed disturbance (vibration) detection.