Optical Fiber Path Testing with Beat-Signal Averaging for DAS and Loss
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Solution Overview
Problem
Existing optical path testing methods face challenges in accurately measuring both physical vibration and loss of an optical fiber using the same light source due to differing requirements for phase noise reduction and fading noise suppression.
Innovation Solution
The optical path testing device and method divide output light into a probe and local optical path, generate modulated pulsed light, and analyze backscattered light using a beat signal to separate frequency bands, applying frequency shift averaging (FSAV) and frequency division multiplexing (FDM) to improve measurement accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the line width of the light source is narrowed to reduce phase noise for vibration measurement, then measurement accuracy of vibration improves, but fading noise suppression capability deteriorates
Solution Approach 1:
The patent segments the measurement process into two distinct modes: vibration measurement mode using a light source with narrow line width to reduce phase noise, and loss measurement mode using the same light source with wide line width to suppress fading noise. The system switches between these modes based on measurement requirements, allowing each measurement type to use optimal light source characteristics without compromise.
Solution Approach 2:
The patent dynamically adjusts the line width of the light source based on the measurement type being performed. The light source can switch between narrow and wide line width configurations, enabling the system to adapt its characteristics to match the specific measurement requirements - narrow for vibration accuracy, wide for fading noise suppression in loss measurements.
2Reliability
If the line width of the light source is widened to suppress fading noise for loss measurement, then fading noise suppression improves, but phase noise increases reducing vibration measurement accuracy
Solution Approach 1:
The patent separates the measurement functions into distinct operational modes. When loss measurement is required, the system uses wide line width to suppress fading noise. When vibration measurement is required, the system switches to narrow line width mode. This segmentation allows each measurement type to use the optimal light source configuration without interference from the other measurement requirements.
3Measurement precision
If frequency shift averaging is applied to suppress fading noise, then measurement time increases, but measurement accuracy of loss improves
Solution Approach 1:
The patent changes the frequency parameter of the light source systematically to implement frequency shift averaging. By varying the frequency across multiple measurements and averaging the results, the system suppresses fading noise and improves loss measurement accuracy. The system optimizes the frequency shift range and number of averaging iterations to balance measurement accuracy with acceptable measurement time.
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 enables simultaneous measurement of physical vibration and loss of an optical fiber with improved accuracy by suppressing phase and fading noise, reducing measurement time, and enhancing sensitivity.
Implementation Method 1
generate a beat signal by causing signal light emitted from one end of an optical fiber when the probe light enters into the one end and input light of the local optical path to interfere with each other
Implementation Method 2
the modulated light is generated by performing, on the output light, modulation based on a frequency changing from a start frequency to an end frequency for a duration of the pulsed light
Implementation Method 3
a method called distributed acoustic sensing (DAS) capable of measuring physical vibration around a measurement target optical fiber by detecting a change in phase caused by a minute change in an optical fiber length due to vibration transmitted to the optical fiber
Implementation Method 4
a method of observing a temporal change in phase of scattered light from each point of an optical fiber
Data Source
AI summary
An optical path testing device and an optical path testing method divide output light from a laser light source into a probe optical path and a local optical path and convert modulated light obtained by modulating input light of the probe optical path into probe light including pulsed light, generate a beat signal by causing signal light and input light of the local optical path to interfere with each other, acquire a signal indicating backscattered light in the optical fiber on the basis of the beat signal, and analyzes a loss distribution, generate the modulated light by performing, on the output light, modulation based on a frequency changing from a start frequency to an end frequency, generate an analysis signal by averaging the backscattered light in each different frequency band included in the beat signal between the different frequency bands and acquire the loss distribution.