Three-Pulse Fiber Grating Demodulation for Polarization Fading
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Polarization-induced fading in distributed interferometric fiber grating vibration sensing systems reduces signal-to-noise ratio and leads to demodulation errors, limiting the system's performance and applicability due to random changes in polarization states caused by optical anisotropy in fibers, which existing methods like optical path full polarization-maintaining technology, polarization diversity reception, Faraday rotator mirror methods, and polarization switching technology are costly and have limitations in visibility and applicability.
Innovation Solution
A grating enhanced distributed vibration demodulation system using three-pulse shearing interference and three-in-three optical coupler digital phase demodulation, where three-pulse light signals with specific polarization states are used to achieve complementary interference visibility, allowing for better path selection and overcoming polarization fading with a visibility greater than 0.7, without the need for costly modifications or active feedback control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If polarization-maintaining devices are used in the optical path, then polarization fading is suppressed, but the system cost increases and reusability decreases
Solution Approach 1:
The patent replaces mechanical polarization-maintaining devices with a digital signal processing approach. By using polarization diversity reception to obtain multiple polarization components and then applying digital demodulation algorithms, the system achieves polarization fading suppression without requiring expensive polarization-maintaining optical components, thus reducing system cost and improving reusability
Solution Approach 2:
The patent changes the parameter of polarization state representation from physical optical path control to digital signal processing. By converting polarization information into digital domain through photodetection and using computational methods to recover the original signal, the system achieves the same effect as polarization-maintaining devices but with different (digital) parameters
2Reliability
If polarization diversity reception with three paths is used, then polarization fading is reduced, but the receiving end complexity increases and minimum visibility is limited to 0.38
Solution Approach 1:
The patent extracts only the necessary polarization components for demodulation rather than using all three paths. By selecting two orthogonal polarization components that contain sufficient information for signal recovery, the system reduces receiving end complexity while maintaining polarization fading resistance and achieving visibility greater than 0.38
Solution Approach 2:
The patent uses partial action by implementing polarization diversity reception with optimized path selection. Instead of fully utilizing all three polarization paths, the system uses a subset of paths that provides sufficient polarization fading resistance, thereby reducing system complexity while maintaining adequate performance
3Reliability
If Faraday rotator mirrors are used at each sensing point, then birefringence effect is cancelled, but the system cost increases significantly
Solution Approach 1:
The patent replaces physical Faraday rotator mirrors with a digital signal processing approach. Instead of using active optical components to cancel birefringence, the system uses polarization diversity reception to capture both polarization states and then applies digital demodulation algorithms to recover the original signal, achieving birefringence compensation without expensive hardware
Solution Approach 2:
The patent creates a digital copy of the polarization information through photodetection. By converting optical polarization states into electrical signals and processing them digitally, the system replicates the function of Faraday rotator mirrors using computational methods, thereby reducing hardware cost while maintaining reliability
4Measurement precision
If polarization switching technology is used, then constant visibility of 1 is achieved, but the system requires active feedback control and polarization switches
Solution Approach 1:
The patent replaces active polarization switching and feedback control with digital signal processing. By using polarization diversity reception to capture both polarization components simultaneously and then applying digital demodulation, the system achieves high visibility without requiring active feedback loops or polarization switches, thus reducing device complexity
Solution Approach 2:
The patent performs preliminary action by capturing both polarization components at the receiving end using polarization diversity reception. This preliminary capture of polarization information allows subsequent digital demodulation to achieve high visibility without requiring real-time feedback control or dynamic switching during the sensing process
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
The system achieves high visibility and resistance to polarization fading, enabling reliable demodulation of interference signals with a simple structure and wide applicability, suitable for applications requiring high signal-to-noise ratio in harsh environments like rail and perimeter security, and fiber hydrophones.
Implementation Method 1
outputting a three-pulse light signal with polarization states of X, X and Y
Implementation Method 2
The phenomenon of birefringence causes a light wave to be decomposed into two kinds of polarized light with vibration directions perpendicular to each other
Implementation Method 3
each fiber grating forming a reflecting surface for reflecting the three-pulse light signal with peak power amplified
Implementation Method 4
forming an interference light signal in a non-equilibrium Michelson interferometer
Implementation Method 5
a first Faraday rotator mirror, a second Faraday rotator mirror
Implementation Method 6
the three-in-three optical coupler performs light splitting processing on interference light to output three paths of interference light signals having a preset phase difference
Implementation Method 7
photoelectric conversion is performed on the three paths of interference light signals having a preset phase difference in a multi-channel photodetector respectively
Implementation Method 8
a first erbium-doped fiber amplifier, a second erbium-doped fiber amplifier
Data Source
AI summary
The present invention discloses a grating enhanced distributed vibration demodulation system based on three-pulse shearing interference, comprising: a laser device, a pulse optical modulator, a three-pulse generation polarization-maintaining structure, a first erbium-doped fiber amplifier, a first optical circulator, a fiber grating array, a second erbium-doped fiber amplifier, a second optical circulator, a three-in-three optical coupler, a first Faraday rotator mirror, a second Faraday rotator mirror, and a four-channel data acquisition card, On the basis of a distributed fiber grating vibration sensing system, three-pulse dislocation interference and three-in-three optical coupler digital phase demodulation technologies are adopted, XX and XY pulses are utilized to complement interference visibility, and demodulation is performed by selecting a better path, so that polarization fading resistance and interference signal high visibility in the distributed fiber grating vibration sensing system are realized.