Brillouin Analysis Sensor Using Faraday Mirror for Polarization Control
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Solution Overview
Problem
BOTDA distributed sensor systems face polarization fading issues when using non-polarization-maintaining fibers, leading to reduced signal intensity and increased acquisition time due to the need for multiple measurements and polarization averaging, which can be affected by mechanical vibrations and fiber changes.
Innovation Solution
The use of a single mode fiber with a Faraday Rotator Mirror and a polarization beamsplitter/combiner to launch orthogonal polarized light waves, ensuring counter-propagating pump and Stokes waves have parallel states of polarization, eliminating polarization fading and allowing simultaneous measurement in both directions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If non-polarization-maintaining fibers are used to reduce cost and improve ease of manufacture, then manufacturing cost decreases and ease of manufacture improves, but polarization fading occurs leading to reduced signal intensity and increased acquisition time
Solution Approach 1:
A polarization beamsplitter/combiner is introduced as an intermediary device to launch orthogonal polarized light waves into the non-polarization-maintaining fiber. This mediator ensures that counter-propagating pump and Stokes waves maintain parallel states of polarization throughout the fiber, preventing polarization fading while allowing the use of cheaper non-PM fibers.
2Measurement precision
If multiple measurements with polarization averaging are performed to compensate for polarization fading, then measurement precision may be maintained, but acquisition time increases and the system becomes more sensitive to mechanical vibrations and fiber changes
Solution Approach 1:
The system performs preliminary action by launching orthogonal polarized light waves with parallel SOPs at the outset, using a polarization beamsplitter/combiner to prepare the light waves before they enter the fiber. This preliminary polarization alignment prevents polarization fading from occurring, eliminating the need for subsequent multiple measurements and polarization averaging, thus reducing acquisition time while maintaining measurement precision.
3Reliability
If polarization-maintaining fibers are used to prevent polarization fading, then signal intensity is maintained, but manufacturing cost increases and the system becomes more complex
Solution Approach 1:
The invention changes the polarization parameters of the launched light waves by using a polarization beamsplitter/combiner to create orthogonal polarized waves with parallel SOPs. This parameter change allows the system to achieve polarization fading prevention in non-PM fibers, eliminating the need for expensive PM fibers while maintaining signal intensity.
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 configuration maintains optimal Brillouin signal intensity by preventing polarization fading, improves signal-to-noise ratio, and simplifies coherent detection, while reducing the need for expensive polarization-maintaining fibers and minimizing the impact of fiber changes.
Implementation Method 1
a phase conjugate mirror (for example a Faraday Rotator Mirror ("FRM")) placed at the far end of the sensing fibre
Implementation Method 2
a polarization beamsplitter/combiner is used to combine polarized cw and pulse waves and launch them with orthogonal polarization states into one end of the SMF fibre
Implementation Method 3
A Brillouin analysis sensor system operates on the principle of Brillouin amplification. In a Brillouin amplifier, a signal (or Stokes) light wave propagating in one direction experiences optical gain if its frequency falls within the Brillouin gain profile of the amplifier pump wave propagating in the opposite direction
Data Source
AI summary
A Brillouin analysis sensor system comprising: a Brillouin analysis sensor; a polarization beam splitter/combiner, operably connected to the Brillouin analysis sensor between the sensor and the sensing fiber, for receiving polarized lightwaves from the sensor, combining the lightwaves and launching combined lightwaves waves in the sensing fiber a first direction, and a phase conjugate mirror at a free end of the sensing fiber for receiving combined lightwaves from the polarization beam splitter/combiner, rotating the polarization of the combined lightwaves and launching the rotated combined lightwaves in the sensing fiber in an opposing direction to the first direction.