Fiber Optic Channel Location Using Reference Keys
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Solution Overview
Problem
Current fiber optic distributed sensing systems lack the precision to determine the physical location of backscattered signals along the fiber optic cable, especially in downhole applications, where accurate repeatable physical depth positioning is required, and existing methods are not sufficiently precise.
Innovation Solution
A method involving a location key with a known physical location, such as an acoustic source, magnetic field source, or acoustically masked section of the fiber optic cable, is used to establish the physical location of the channel, allowing for precise location determination using techniques like Lorentz force, time-of-day measurement, or ambient noise analysis.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If optical time-domain reflectometry (OTDR) methods are used to infer location based on timing and fiber refraction index, then the system can provide rough location estimates, but the measurement precision deteriorates to the point where uncertainties build to significant magnitude over fiber length
Solution Approach 1:
The patent introduces location keys that are pre-installed at known physical locations along the fiber optic cable before deployment. These location keys serve as reference points that are established in advance, allowing the system to perform preliminary calibration and establish accurate physical location mappings before actual sensing operations begin. This preliminary action eliminates the need for rough inferential calculations during operation.
Solution Approach 2:
The location keys act as intermediary elements between the OTDR system and the physical environment. Instead of directly measuring location through timing and refraction index calculations, the system uses location keys as mediators that provide known reference points. These intermediaries enable accurate location determination by providing physical reference markers that can be detected and correlated with fiber channel positions.
2Reliability
If rough location inference based on timing and refraction index is used, then the system can operate without additional equipment, but the reliability of location determination deteriorates for applications requiring 1 meter or better accuracy
Solution Approach 1:
The patent divides the fiber optic cable into segments or channels, each associated with a specific location key. By segmenting the cable and assigning known location references to specific segments, the system achieves reliable location determination for each segment independently. This segmentation approach allows the system to maintain high reliability without requiring complex continuous measurement systems throughout the entire cable length.
Solution Approach 2:
The location keys are designed to be self-identifying reference points that provide their own location information. Once installed at known positions, these keys automatically serve as reference markers without requiring external calibration or continuous adjustment. The system uses these self-service reference points to establish accurate location mappings, reducing the need for complex external calibration equipment or procedures.
Data Source
AI summary
A method for determining the physical location of a fiber optic channel in a fiber optic cable comprises the steps of a) providing at least one location key having a known physical location, b) establishing the location of the location key with respect to the fiber optic channel, and c) using the location information established in step b) to determine the physical location of the channel. The location key may comprises an acoustic source, a section of fiber optic cable that is acoustically masked, or at least one magnetic field source and step b) comprises using a Lorentz force to establish the location of the magnetic field source with respect to the fiber optic channel.