Coherent DAS Drift Compensation Using Phase Difference Averaging
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Laser frequency drift in distributed acoustic sensing systems complicates the differentiation of environmental disturbances from optical phase changes, making it difficult to accurately detect seismic and other acoustic events along the length of an optical fiber.
Innovation Solution
Employing a narrow linewidth CW laser at the transmitter and receiver sides, combined with phase difference averaging and circuitry to track and eliminate laser frequency drift, using a pre-set fixed step to generate a frequency-shift carrier signal, converting the input to a lower frequency and removing laser drift at the output.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If laser frequency drift is present in the system, then the detection of environmental disturbances becomes difficult, but using narrow linewidth CW laser reduces the processing speed
Solution Approach 1:
The patent implements a feedback mechanism where the detected signal is fed back through a phase difference averaging circuit to track and compensate for laser frequency drift. This feedback loop continuously adjusts the phase reference to maintain accurate detection despite laser frequency variations, resolving the contradiction between measurement precision and processing speed.
Solution Approach 2:
The patent changes the parameter of phase difference averaging to track frequency drift. By dynamically adjusting the phase reference based on averaged phase differences from the detected signal, the system compensates for laser frequency drift without sacrificing processing speed, maintaining both detection accuracy and operational speed.
2Reliability
If phase difference averaging is used to track frequency drift, then laser frequency drift is eliminated, but device complexity increases
Solution Approach 1:
The patent segments the signal processing into distinct functional stages: coherent detection, phase difference calculation, averaging for drift tracking, and frequency shift generation. This segmentation allows each component to perform its specific function efficiently, managing overall system complexity while improving laser frequency stability through specialized processing blocks.
Solution Approach 2:
The patent introduces an intermediary phase difference averaging circuit that mediates between the detected signal and the final frequency compensation. This intermediary component processes the phase information and generates corrected frequency references, simplifying the overall architecture by breaking down the complex drift compensation task into manageable intermediate steps.
3Measurement precision
If coherent detection with narrow linewidth laser is used, then detection sensitivity is improved, but laser frequency drift becomes more pronounced
Solution Approach 1:
The patent converts the harmful effect of laser frequency drift into a beneficial tracking opportunity. By using the phase differences caused by frequency drift as input to the averaging circuit, the system learns and compensates for the drift, turning the instability problem into a self-correcting feature that improves long-term frequency stability while maintaining high detection sensitivity.
Solution Approach 2:
The patent performs preliminary phase difference averaging to track frequency drift before the final detection decision is made. This preliminary action continuously updates the phase reference in anticipation of frequency variations, ensuring that when the actual detection occurs, the system is already compensated for drift effects, maintaining both sensitivity and stability.
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
The solution effectively compensates for laser frequency drift, enabling precise detection of environmental disturbances by eliminating laser-induced noise and improving the accuracy of acoustic event detection in distributed acoustic sensing systems.
Implementation Method 1
a transmitter launches unmodulated signals from a continuous wave (CW) laser into an optical fiber
Implementation Method 2
a coherent receiver extracts any optical phase change
Implementation Method 3
a coherent receiver extracts any optical phase change
Implementation Method 4
Another narrow linewidth CW laser is used to coherently detect the received signal
Implementation Method 5
circuitry configured to perform a phase difference averaging to track the low-speed frequency drift
Implementation Method 6
This other, second stage uses the phase from the sum of the pre-set value and the value outputted from the first stage, to generate the frequency-shift carrier signal and convert the input to a lower frequency
Data Source
AI summary
Disclosed is a forward phase method using regular narrow line width CW laser, to cover the acoustic band with reduced processing speed, while tolerant laser frequency drift. A narrow linewidth CW laser is used to launch its power into an optical fiber at a transmitter side. At a receiver side, another narrow linewidth CW laser is used to coherently detect the received signal. The detected signal, which includes both X and Y polarizations, each having in-phase and quadrature to represent a “complex” channel, are connected to an ADC's inputs. Signal processing following the ADC inputs and extracts the phase change of the acoustic band.