Optical Fiber Strain Measurement Using Synchronized Modulation
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Solution Overview
Problem
Conventional optical-fiber-characteristic measuring methods using Brillouin scattering have limited spatial resolution and are hindered by high noise levels, making it difficult to accurately measure strain distributions in long optical fibers, especially when strains are large or the measurement range needs to be extended.
Innovation Solution
The method involves frequency modulation of light from a light source, combined with intensity modulation synchronized with the frequency modulation, to adjust the spectrum distribution of the output light, thereby reducing noise and enhancing the peak frequency measurement precision while extending the measurement range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional time-resolving measurement method using light pulses is used, then the measurement can be performed, but the measurement time is long (several minutes to ten minutes) and spatial resolution is limited (maximum: 1 m)
Solution Approach 1:
The patent applies periodic frequency modulation to the continuous light wave at the modulation frequency fm, creating periodic correlation peaks along the optical fiber. This periodic action enables continuous measurement with high spatial resolution (1 cm) and fast sampling rate (60 Hz), eliminating the long measurement time and limited resolution of pulse-based methods.
2Length of stationary object
If the measurement range is extended by lowering the frequency-modulation frequency, then the measurement range increases, but the spatial resolution deteriorates and becomes a large value
Solution Approach 1:
The patent dynamically adjusts the frequency-modulation frequency fm and modulation amplitude Δf based on the desired measurement range and spatial resolution. By optimizing these parameters together, the system achieves both extended measurement range (up to 10 km) and maintained high spatial resolution (1 cm), resolving the trade-off between measurement range and resolution.
3Length of stationary object
If the measurement range is extended, then the coverage area increases, but the noise level from integrated unnecessary components increases, deteriorating measurement precision
Solution Approach 1:
The patent extracts only the correlation peak signal at the specific modulation frequency fm from the total Brillouin scattering spectrum. By using frequency-domain filtering and synchronous detection at the modulation frequency, the system separates the useful signal from the integrated noise of non-correlation positions, maintaining high signal-to-noise ratio even for extended measurement ranges.
4Length of stationary object
If frequency modulation amplitude is increased to maintain spatial resolution while extending measurement range, then the measurement range extends, but the spectrum distribution becomes uneven with high noise at frequency edges
Solution Approach 1:
The patent applies local quality adjustment by modifying the frequency modulation waveform to concentrate energy at the center frequency and reduce energy at the frequency edges. This creates a more uniform spectrum distribution, reducing noise levels at the frequency edges while maintaining the measurement range and spatial resolution.
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 the signal-to-noise ratio, allowing for precise measurement of strain distributions with higher spatial resolution and extended measurement ranges, even under large strain conditions.
Implementation Method 1
a light source unit which outputs light having undergone frequency modulation
Implementation Method 2
the optical-fiber-characteristic measuring apparatus further comprises intensity modulating means for modulating an intensity of the output light in synchronization with the frequency modulation of the light source unit
Implementation Method 3
probe light generating means for performing frequency shift on the output light from the light source unit and inputting that light as probe light into one end of a measurement-target optical fiber
Implementation Method 4
measuring means for detecting a Brillouin gain of the probe light output from the measurement-target optical fiber while sweeping a frequency difference between the pump light and the probe light
Implementation Method 5
Brillouin scattering which occurs in an optical fiber changes in accordance with a strain applied to the optical fiber. A technology which measures the distribution of strains along the lengthwise direction of an optical fiber using such a phenomenon has been developed. That technology enables the measurement of the size of a strain by measuring the frequency change in Brillouin scattering light
Implementation Method 6
intensity modulating means for modulating an intensity of the output light in synchronization with the frequency modulation of the light source unit
Data Source
AI summary
A measurement precision is improved and a measurement range is extended by efficiently suppressing a noise level of integrated unnecessary components from non-correlation positions. Measuring means 33 detects the Brillouin gain of a probe light output from a measurement-target optical fiber FUT while sweeping a frequency difference between the pump light and the probe light, and measures the distribution of strains of the measurement-target optical fiber FUT. An optical intensity modulator 4 performs intensity modulation on output light in synchronization with frequency modulation performed on a light source 1. Accordingly, the spectrum distribution with respect to the frequency of light from the light source 1 can be adjusted arbitrarily, and a noise spectrum shape generated at a position other than a correlation peak position and spreading over a frequency axis can be adjusted, and the peak frequency of a Lorentz spectrum generated at the correlation peak position can be measured precisely. Moreover, a measurement range dm can be extended.