Strain Change Measurement Using Inverted Chirped Pulses
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Solution Overview
Problem
Existing methods for measuring strain changes in branched optical fibers, such as OFDR and frequency scanning OTDR, face challenges in achieving high sampling rates and spatial resolution due to the need for extensive frequency sweeps and fine optical frequency scans, which limits their effectiveness in detecting dynamic strain changes.
Innovation Solution
A strain change measurement apparatus and method that uses first and second chirped pulsed light with inverted chirps to maximize correlation between waveforms, allowing for the calculation of strain changes at high sampling rates by shifting the time axis of the first scattered light waveform to match the second scattered light waveform.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If OFDR or frequency scanning OTDR methods are used to measure strain changes in branched optical fibers, then measurement precision is improved, but sampling rate deteriorates due to the need for extensive frequency sweeps and fine optical frequency scans
Solution Approach 1:
The patent inverts the conventional approach by using time-axis inversion of chirped pulses instead of frequency sweeping. The first chirped pulsed light has a chirp with frequency increasing over time, while the second has frequency decreasing over time. This inversion allows correlation-based measurement without extensive frequency scans, resolving the contradiction between measurement precision and sampling rate
Solution Approach 2:
The patent changes the measurement parameter from frequency domain (OFDR) or scanned frequency intensity (frequency scanning OTDR) to time-domain correlation between inverted chirped pulses. By shifting the time axis of the first scattered light waveform to match the second scattered light waveform, the system achieves high sampling rate strain measurement without sacrificing precision
2Measurement precision
If extensive frequency sweeps are performed to achieve targeted sensitivity in vibration pattern detection, then measurement precision is improved, but measurement time increases
Solution Approach 1:
Instead of performing extensive frequency sweeps to achieve sensitivity, the patent uses time-axis inversion of chirped pulses and correlation measurement. This approach achieves vibration pattern detection sensitivity without the time penalty of frequency sweeping, as the correlation method processes the entire frequency range simultaneously in the time domain
3Measurement precision
If fine optical frequency scans are performed to achieve targeted sensitivity, then measurement precision is improved, but productivity deteriorates
Solution Approach 1:
The patent fundamentally changes the measurement parameter from optical frequency scan domain to time-domain correlation. By using chirped pulses with opposite chirp directions and measuring the time shift between correlated waveforms, the system achieves fine strain measurement sensitivity without performing slow frequency scans, thereby improving measurement speed and productivity
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
Enables high sampling rate measurement of strain changes in branched optical fibers, improving spatial resolution and enabling detection of dynamic strain changes, even in long-distance fiber networks with branched configurations.
Implementation Method 1
a phase of Rayleigh scattered light backscattered from each point is measured
Data Source
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AI summary
An object of the present disclosure is to measure, at a high sampling rate, a distribution of a vibration pattern applied to each core after being branched. A strain change measurement apparatus according to the present disclosure inputs, at a reference time, first chirped pulsed light having a chirp having a frequency changing linearly with time to a measurement target optical fiber branched by a coupler, acquires a signal of first scattered light regarding the first chirped pulsed light, inputs, at each monitoring time, second chirped pulsed light having a chirp obtained by time axial inversion with respect to the first chirped pulsed light to the measurement target optical fiber to acquire a signal of second scattered light regarding the second chirped pulsed light, determines a shift amount allowing for maximization of a correlation between a waveform obtained by inverting the signal of the first scattered light around the time axis and further shifting and a waveform of the signal of the second scattered light, and uses the shift amount to calculate a change in strain amount in the measurement target optical fiber from the reference time to each monitoring time.