Spatial Filter for Multimode Fiber Brillouin OTDR
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Solution Overview
Problem
Conventional Brillouin OTDR systems are limited in flexibility due to their design for single-mode optical fibers, making them ineffective for measuring characteristics in multimode optical fibers, where the frequency spacing between the Brillouin backscattered light and the probe pulse is not adequately separated.
Innovation Solution
A spatial filter is used to pass a portion of the Brillouin backscattered light from multimode optical fibers, ensuring a consistent optical phase distribution, allowing for effective detection and processing of the signal, which can be achieved using either a single-mode optical fiber or an opaque layer with an opening, applied in either the near-field or far-field, to facilitate measurements in multimode fibers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional Brillouin OTDR systems use single-mode optical fibers, then the frequency spacing between Brillouin backscattered light and probe pulse is adequately separated, but the system loses flexibility and cannot measure characteristics in multimode optical fibers
Solution Approach 1:
The patent introduces a spatial filter as an intermediary component between the multimode optical fiber and the detection equipment. This spatial filter selectively passes only the phase-coherent portion of the Brillouin backscattered light, enabling frequency separation in multimode fibers without requiring single-mode fibers. The spatial filter acts as a mediator that resolves the contradiction by filtering out incoherent light that would otherwise interfere with the measurement.
Solution Approach 2:
The patent changes the parameter of optical phase coherence by using a spatial filter to select only phase-coherent light components. This parameter change enables the system to achieve effective frequency separation in multimode fibers, transforming the system from being unable to measure multimode fibers to successfully measuring strain and temperature in multimode fibers with improved adaptability.
2Reliability
If Brillouin OTDR systems are designed for single-mode optical fibers, then signal separation is effective, but the system cannot effectively measure characteristics in multimode optical fibers
Solution Approach 1:
The patent makes the Brillouin OTDR system universal by enabling it to work with both single-mode and multimode optical fibers. The spatial filter component allows the system to maintain effective signal separation while adapting to different fiber types, achieving multi-functionality. The system can now be applied in diverse environments including wellbores and land-based or marine settings using either fiber type.
Solution Approach 2:
The spatial filter serves as an intermediary that enables reliable signal separation in multimode fibers. By filtering to pass only phase-coherent light, it maintains the reliability of Brillouin signal detection while allowing the system to work with multimode fibers, thus resolving the contradiction between signal separation effectiveness and adaptability to different fiber types.
3Quantity of substance
If the entire Brillouin backscattered light from multimode optical fiber is passed to detection equipment, then all signal information is captured, but phase incoherence reduces measurement accuracy
Solution Approach 1:
The patent extracts only the phase-coherent portion of the Brillouin backscattered light using a spatial filter. Instead of passing all light to the detection equipment, it selectively extracts the coherent component that carries accurate measurement information. This extraction resolves the contradiction by removing the incoherent light that would degrade measurement precision while maintaining sufficient signal quantity for accurate strain and temperature measurements.
Solution Approach 2:
The patent applies local quality by ensuring that only light with consistent optical phase (phase-coherent light) is passed to the detection equipment. The spatial filter creates a local quality condition where the transmitted light has uniform phase characteristics, which is essential for accurate Brillouin frequency measurement. This selective quality control resolves the contradiction between capturing all signal information and maintaining measurement accuracy.
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 flexible Brillouin OTDR systems to measure strain and temperature in multimode optical fibers, enhancing their applicability in various environments, including wellbores and land-based or marine settings, by ensuring phase-coherent light is passed to detection equipment, thereby improving the accuracy and reliability of measurements.
Implementation Method 1
Brillouin scattering is an inelastic phenomenon that results from the interaction of incident optical photons (of an incident optical signal) with acoustic phonons in the medium (the optical fiber)
Implementation Method 2
a spatial filter to pass a portion of Brillouin backscattered light from the multimode optical fiber
Data Source
AI summary
To measure a characteristic of a multimode optical fiber, a light pulse source produces a light pulse for transmission into the multimode optical fiber. A spatial filter passes a portion of Brillouin backscattered light from the multimode optical fiber that is responsive to the light pulse. Optical detection equipment detects the portion of the Brillouin backscattered light passed by the spatial filter.