Multispan Optical Fiber System for Distributed Acoustic Sensing
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Solution Overview
Problem
Current distributed acoustic sensing (DAS) systems are limited in range and sensitivity, typically only able to sense up to 50 km to 150 km and are restricted to sensing with a single fiber span, due to limitations in noise floor power spectral density and signal-to-noise ratio.
Innovation Solution
The implementation of a DAS system that includes a DAS station with a transmitter and receiver, utilizing two acousto-optic modulators and narrow bandwidth optical filters to enhance signal sensitivity, and a frequency shift tracker to maintain signal quality within the receiver bandwidth, along with a power tracker to manage signal power across the sensing span.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If the sensing distance is extended beyond 50-150 km, then the range of DAS system is improved, but the noise floor power spectral density increases and signal-to-noise ratio deteriorates
Solution Approach 1:
The optical fiber sensing system is divided into multiple spans, each with its own amplification and filtering stages. The fiber cable is segmented into sections that can be independently managed and amplified, allowing extended sensing distance while maintaining signal quality through distributed signal regeneration.
Solution Approach 2:
Acousto-optic modulators are introduced as intermediary devices to convert optical signals to acoustic signals and back, enabling signal regeneration and noise filtering at intermediate points along the fiber span. This intermediary conversion process allows the system to maintain signal-to-noise ratio over extended distances by actively managing signal quality at each stage.
2Measurement precision
If acousto-optic modulators and narrow bandwidth optical filters are added to increase sensing sensitivity, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The acousto-optic modulators serve multiple functions simultaneously: they act as signal amplifiers, frequency shifters, and noise filters. The narrow bandwidth optical filters provide both signal purification and noise rejection. This multi-functionality reduces the need for separate dedicated components, thereby managing system complexity while achieving high sensing sensitivity.
Solution Approach 2:
The system dynamically adjusts the bandwidth parameter of optical filters and the operating frequency of acousto-optic modulators to optimize sensing sensitivity for different conditions. By changing these parameters rather than adding fixed components, the system achieves adaptability and high sensitivity without proportionally increasing complexity.
3Length of stationary object
If signal power is increased to extend sensing range, then range is improved, but non-linear interference and stimulated Brillouin scattering increase
Solution Approach 1:
The system uses periodic pulsing of the laser source with carefully controlled duty cycles and repetition rates. This periodic operation allows the fiber to cool between pulses, preventing thermal accumulation that leads to stimulated Brillouin scattering. The intermittent signaling also reduces average power in the fiber, minimizing non-linear interference while maintaining sufficient peak power for extended range sensing.
Solution Approach 2:
Acousto-optic modulators are used to pre-modulate the signal before it enters high-loss or high-risk fiber sections, preparing the signal in advance to avoid conditions that trigger non-linear effects. The system proactively manages signal characteristics before problematic conditions arise, preventing stimulated Brillouin scattering and non-linear interference rather than reacting to them.
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 significantly increases the sensitivity and range of DAS systems by reducing noise floor, improving signal-to-noise ratio, and maintaining signal integrity over longer distances, thereby extending the effective sensing range beyond traditional limitations.
Implementation Method 1
two acousto-optic modulators and narrow bandwidth optical filters to enhance signal sensitivity
Implementation Method 2
narrow bandwidth optical filters to enhance signal sensitivity
Implementation Method 3
a DAS receiver, arranged to receive a backscattered Rayleigh signal, based upon the DAS signal
Data Source
AI summary
A distributed acoustic sensing system. The DAS system may include a distributed acoustic sensing (DAS) station, comprising: a DAS transmitter, arranged to launch an outbound DAS signal through an optical fiber, over at least one span; a DAS receiver, arranged to receive a backscatter Rayleigh signal, based upon the DAS signal; and at least one component, coupled to the DAS transmitter, the DAS receiver, or both, and arranged to increase a sensitivity for sensing of the DAS system.