Optical Fiber Vibration Sensor SNR Management via Differential Rayleigh Processing

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Solution Overview

Problem

Existing optical fiber vibration sensors face challenges in maintaining a high signal-to-noise ratio due to noise sources like temporal pulse intensity fluctuation, laser phase noise, and thermal noise, which limits the maximum detectable vibration frequency when using averaging techniques.

Innovation Solution

The method involves transmitting optical pulses through an optical fiber, detecting backscattered Rayleigh traces, and calculating a normalized differential trace without averaging, allowing for the determination of vibration location and frequency up to the Nyquist frequency, using a system that includes a light pulse generator, optical circulator, polarization controllers, and a photodetector to enhance signal processing efficiency.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If averaging technique is used to mitigate intensity fluctuation, then signal-to-noise ratio is improved, but maximum detectable vibration frequency is reduced

Engineering Contradiction:

Improvesignal-to-noise ratioVSAvoidmaximum detectable vibration frequency

Core Design Contradiction:

Measurement precisionVSSpeed

Solution Approach 1:

The patent extracts only the differential information between consecutive Rayleigh traces by calculating ΔR = R_i - R_{i-1}, removing the need for averaging while preserving the vibration signal. This differential operation isolates the changing components (vibrations) from the static components (intensity fluctuations), resolving the contradiction between SNR improvement and frequency detection capability.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

Instead of averaging multiple traces to reduce noise (conventional approach), the patent inverts the approach by taking the difference between consecutive traces. This inversion reveals that differential processing inherently suppresses stationary noise while preserving dynamic vibration signals, achieving both high SNR and high frequency detection without the trade-off.

Inventive Principle:

Principle #13The other way round (Inversion)

2Reliability

If more traces are averaged to improve signal stability, then noise is reduced, but sampling rate is effectively reduced

Engineering Contradiction:

Improvestability of recorded Rayleigh tracesVSAvoideffective sampling rate

Core Design Contradiction:

ReliabilityVSProductivity

Solution Approach 1:

The patent extracts the essential vibration information by computing the difference between consecutive traces, eliminating the need to accumulate multiple averaged traces. This extraction approach achieves noise reduction through differential cancellation while maintaining the full sampling rate, as each trace difference is computed independently without requiring N consecutive traces.

Inventive Principle:

Principle #2Taking out (Extraction)

3Measurement precision

If traditional averaging method is used, then intensity fluctuation is mitigated, but frequency response is limited to below Nyquist frequency

Engineering Contradiction:

Improveintensity fluctuation mitigationVSAvoidfrequency response accuracy

Core Design Contradiction:

Measurement precisionVSManufacturing precision

Solution Approach 1:

The patent inverts the conventional averaging approach by using differential processing (subtraction instead of addition). This inversion demonstrates that differencing consecutive traces naturally suppresses low-frequency intensity fluctuations while preserving high-frequency vibration signals, enabling frequency response up to the Nyquist limit without the roll-off characteristic of averaging methods.

Inventive Principle:

Principle #13The other way round (Inversion)

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 approach improves noise equalization and enables the detection of vibrations with frequencies up to the Nyquist limit, enhancing the system's ability to identify weak vibrations and processing data with greater speed and efficiency without the need for data averaging.

Implementation Method 1

Each Rayleigh trace has a speckle-like profile because of coherent interference of the signals reflected by scattering centers within the injected pulse duration

Methodology Applied

Scientific EffectRayleigh backscattering: Rayleigh Scattering

Implementation Method 2

When an acoustic signal is applied at a position along the FUT, the effective refractive index changes at this position, and consequently the intrusion can be sensed by observing the intensity fluctuation of a corresponding speckle in the recorded traces

Methodology Applied

Scientific EffectAcoustic modulation of refractive index:

Data Source

PatentUS11698288B2Signal to noise ratio management

Publication Date: 2023.07.11 SAUDI ARABIAN OIL CO

AI summary

The subject matter of this specification can be embodied in, among other things, a method for remotely sensing vibration includes transmitting a collection of optical pulses through an optical fiber at a predetermined frequency, detecting a collection of backscattered Rayleigh traces from the optical fiber based on a vibration of the optical fiber at a vibration frequency at a location along the optical fiber, determining a normalized differential trace based on the collection of Rayleigh traces, determining, based on the normalized differential trace, the location in the optical fiber of the vibration, and determining, based on the raw Rayleigh traces, the vibration frequency.