Self-Heterodyne φ-OTDR System with Multi-Spatial Resolution
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Solution Overview
Problem
Current distributed optical fiber sensing systems face challenges with coherent fading noise, phase noise, and pseudo-random noise due to frequency drift and random distribution of Rayleigh scattering points, leading to reduced signal-to-noise ratio and detection performance, especially in achieving optimal spatial resolution for vibration sensing.
Innovation Solution
A self-heterodyne φ-OTDR system with a free multi-spatial resolution is implemented using acousto-optic modulators with a shared driver, a narrow linewidth laser, and time-delay fibers to suppress noise and adjust spatial resolution dynamically, enabling effective suppression of coherent fading noise and optimizing signal resolution based on event length.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If traditional φ-OTDR system uses single spatial resolution, then system structure is simple, but cannot adapt to different vibration event lengths and achieves optimal SNR for all scenarios
Solution Approach 1:
The patent divides the single probe light into multiple probe lights with different pulse intervals using a 1×N fiber optic coupler and N AOMs. Each probe light is assigned a specific spatial resolution, allowing the system to simultaneously monitor multiple spatial scales. This segmentation enables adaptation to different vibration event lengths without requiring a completely different system configuration for each scenario.
Solution Approach 2:
The patent implements dynamic spatial resolution selection by allowing the system to switch between different probe lights with different pulse intervals based on the detected vibration event characteristics. The controller dynamically selects which probe light to use, enabling the system to adapt its spatial resolution to match the expected event length, thereby optimizing SNR for specific application scenarios.
2Reliability
If laser frequency drifts, then system can maintain operation, but introduces phase noise and pseudo-random noise reducing SNR
Solution Approach 1:
The patent introduces a local oscillator light as an intermediary reference. Instead of directly measuring the phase of the probe light which is affected by laser frequency drift, the system mixes the probe light with the local oscillator light to create a beat signal. The phase information is extracted from this beat signal, which references a stable local oscillator, thereby compensating for the frequency drift of the main laser and reducing phase noise and pseudo-random noise.
3Area of stationary object
If Rayleigh scattering points are randomly distributed, then sensing covers entire fiber, but coherent fading effect occurs reducing detection performance
Solution Approach 1:
The patent segments the sensing process into multiple independent channels, each using a probe light with a specific pulse interval and spatial resolution. By dividing the measurement into separate channels with different temporal characteristics, the system reduces the coherent fading effect that occurs when scattering points are randomly distributed. Each channel independently measures its specific spatial resolution, and the results are combined to provide comprehensive sensing coverage while maintaining detection performance.
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 effectively suppresses coherent fading noise and phase noise, allowing for optimal spatial resolution selection, thereby enhancing the signal-to-noise ratio and detection performance for vibration sensing applications.
Implementation Method 1
a plurality of acousto-optic modulators (AOMs) using the same driver are used to couple probe light with different pulse intervals and different frequency shifts
Implementation Method 2
a φ-OTDR is the most developed and widely used distributed optical fiber sensing technology based on Rayleigh backscattering (RBS), which utilizes a coherent fading effect between RBS for sensing measurement
Implementation Method 3
a photodetector, an electrical amplifier, three filters, a data acquisition card
Data Source
AI summary
A self-heterodyne phase-sensitive optical time domain reflectometry (φ-OTDR) system with a free multi-spatial resolution includes a narrow linewidth laser source, a 1×3 fiber-optic coupler, three acousto-optic modulators (AGMs), a 3×1 fiber-optic coupler, two time-delay fibers, an erbium-doped fiber amplifier (EDFA), a circulator, a photodetector, an electrical amplifier, three filters, a data acquisition card, a pulse signal generator, and a driver module. A plurality of acousto-optic modulators using the same driver are used to couple probe light with different pulse intervals and different frequency shifts and then inject the probe light into a fiber, such that a self-heterodyne detection structure with a multi-spatial resolution is implemented, which suppressed optical background noise such as coherent fading noise, phase noise introduced by a frequency drift of a light source, and pseudo-random noise (PRN).