Polarization-Based DAS Fiber Sensing With Low-Coherence Lasers
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Solution Overview
Problem
Existing distributed acoustic sensing (DAS) systems face challenges in achieving high sensitivity and long sensing range while maintaining cost-effectiveness due to stringent requirements on laser linewidth and coherence length, particularly in applications involving interference of backscattered light from different locations along the sensing fiber.
Innovation Solution
The proposed DAS system utilizes polarization-based sensing by measuring variations in the state of polarization (SOP) of backscattered light to detect local phase disturbances, allowing for the use of low-cost lasers with wider linewidths and relaxed coherence length requirements, and incorporates optical components such as SOAs and polarimeters to enhance sensitivity and range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional interference-based DAS methods are used, then high sensitivity can be achieved, but stringent requirements on laser linewidth and coherence length increase system cost and complexity
Solution Approach 1:
The patent introduces polarization state as an intermediary parameter to bridge the acoustic disturbance and the detected light signal. Instead of directly measuring interference patterns that require stringent laser coherence, the system measures polarization changes caused by acoustic-induced phase disturbances, thereby relaxing laser requirements while maintaining sensitivity
Solution Approach 2:
The patent changes the measurement parameter from traditional intensity-based interference to polarization state of polarization (SOP) measurements. By detecting changes in polarization parameters (Stokes parameters) rather than relying on coherent interference patterns, the system achieves high sensitivity without requiring narrow linewidth lasers or long coherence lengths
2Measurement precision
If traditional interference-based DAS methods are used, then high sensitivity can be achieved, but coherence length requirements reduce system adaptability to different applications
Solution Approach 1:
The patent changes the fundamental measurement parameter from coherent interference intensity to polarization state. This parameter transformation enables the system to work with standard lasers having wider linewidths, thereby adapting to diverse applications including seismic detection, infrastructure monitoring, and security sensing without requiring application-specific laser customization
Solution Approach 2:
Polarization state serves as a universal intermediary that translates acoustic disturbances into measurable optical signals. This intermediary approach decouples the sensing mechanism from laser coherence requirements, enhancing adaptability across different sensing applications and environments
3Ease of manufacture
If polarization-based sensing is used, then laser cost is reduced, but detection sensitivity must be maintained through alternative means
Solution Approach 1:
The patent substitutes traditional interference-based detection with polarization-based detection. Instead of relying on coherent interference patterns that require expensive narrow-linewidth lasers, the system uses polarization state measurements that can be performed with standard lasers and specialized polarimetric detectors, reducing cost while maintaining sensitivity
Solution Approach 2:
By changing from intensity-based interference measurement to polarization state measurement, the system can use inexpensive broadband lasers. The polarization detection methodology compensates for the relaxed laser requirements by measuring Stokes parameters that are sensitive to acoustic-induced phase changes, thereby maintaining detection sensitivity with lower-cost laser sources
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
This approach enables high sensitivity and long-range acoustic sensing with reduced laser costs, utilizing low-cost lasers and optical components to detect acoustic vibrations and stresses along the sensing fiber, thereby improving detection capabilities.
Implementation Method 1
an optical modulator located to receive the laser light from the laser to produce laser pulses for sensing local phase disturbances
Implementation Method 2
cause scattering of the laser pulses to generate backscattered light
Implementation Method 3
an optical polarimeter to receive a portion of the backscattered light returned from the sensing fiber to measure Stokes parameters of state of optical polarization of the backscattered light
Data Source
AI summary
This patent document discloses designs of distributed acoustic sensing (DAS) fiber sensors that making distributed acoustic sensing measurements using a sensing fiber based on variations over time of the state of polarization of backscattered light returned from the sensing fiber to extract local phase disturbances at various locations along the sensing fiber.