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A fully digital MIMO-OFDM scheme for fading mitigation in coherent Δϕ-OTDR.
Optics Express
|November 23, 2021
Summary
We developed a new fiber optic sensing method using coherent MIMO-OFDM to overcome signal fading. This technique significantly improves sensitivity and reduces false alarms in distributed strain sensing.
Area of Science:
- Optical Engineering
- Sensing Technology
- Signal Processing
Background:
- Distributed fiber optic sensing techniques like Delta-Phi Optical Time Domain Reflectometry (Δϕ-OTDR) are crucial for structural health monitoring.
- Coherent fading is a significant challenge in Δϕ-OTDR, limiting its sensitivity and reliability.
- Existing methods struggle to achieve high sensitivity and a wide dynamic range simultaneously over standard telecom fibers.
Purpose of the Study:
- To introduce a novel coherent MIMO-OFDM based sensing technique for Δϕ-OTDR.
- To mitigate the coherent fading issue inherent in Δϕ-OTDR systems.
- To enhance the overall sensing sensitivity and reliability of fiber optic sensors.
Main Methods:
- Utilizing digital frequency division multiplexing of probing codes with Orthogonal Frequency Division Multiplexing (OFDM).
- Probing the optical channel across multiple electrical subcarriers and combining responses based on a reliability criterion.
- Implementing a coherent Multiple-Input Multiple-Output (MIMO) configuration with OFDM (MIMO-OFDM).
Main Results:
- Demonstrated mitigation of coherent fading in Δϕ-OTDR.
- Achieved a decrease in the noise floor for sensing measurements on standard single mode fiber (SSMF).
- Reported a measured sensitivity level below 21 pε/√Hz over 1.3km fiber with a 760Hz mechanical bandwidth.
- Showcased an enhancement in the dynamic range for detecting mechanical excitation, exceeding 18dB compared to single-carrier probing.
Conclusions:
- The coherent MIMO-OFDM Δϕ-OTDR technique effectively addresses coherent fading.
- This method significantly enhances sensing sensitivity and reduces false alarms in fiber optic sensing.
- The technique offers improved performance for detecting mechanical excitations over standard telecom fibers.
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