Interferometric Optical Fiber Sensor Interrogation
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Solution Overview
Problem
Existing optical fibre sensor systems face limitations in multiplexing a large number of interferometric sensors along a fibre while maintaining high sensor phase resolution and dynamic range, due to low optical power levels and reduced dynamic range caused by increased sensor density.
Innovation Solution
A method involving continuous and repeated frequency sweeping of interrogation light within a sensor array, using a laser source and local oscillator for coherent detection, allowing for high sensitivity and spatially resolved interrogation, and employing discrete reflectors for improved signal-to-noise ratio and reduced phase noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If time division multiplexing with pulsed interrogation is used to increase the number of sensors along a fibre, then the number of multiplexed sensors is improved, but the dynamic range and sensor phase resolution deteriorate due to lower time averaged optical power at the receiver
Solution Approach 1:
The patent applies periodic frequency sweeping of the laser source, where the optical frequency is continuously modulated in a periodic manner across a defined bandwidth. This periodic frequency modulation allows multiple sensors to be distinguished based on their temporal delay profiles while maintaining continuous wave operation, thereby preserving optical power levels and sensor phase resolution even when a large number of sensors are multiplexed along the fibre
Solution Approach 2:
The patent transitions from time-domain separation using pulsed interrogation to frequency-domain separation using continuous frequency sweeping. By moving the discrimination dimension from temporal pulse timing to optical frequency modulation, the system achieves multi-sensor capability while maintaining continuous wave operation and avoiding the power reduction penalties associated with pulsed schemes
2Adaptability or versatility
If pulsed interrogation is used to separate sensor sections along the fibre in time, then distributed sensing capability is improved, but the optical power levels returned to the receiver deteriorate
Solution Approach 1:
The patent employs continuous wave interrogation with continuous frequency sweeping, eliminating the pulsed operation that causes optical power loss. The frequency sweep continues uninterrupted, allowing the system to maintain high optical power levels at the receiver while still achieving distributed sensing capability through frequency-domain analysis of the continuous return signal
3Quantity of substance
If the number of time-multiplexed sensors is increased, then the sensor density is improved, but the dynamic range deteriorates due to reduced time averaged optical power
Solution Approach 1:
The patent changes the fundamental operating parameter from pulsed temporal modulation to continuous frequency modulation. By sweeping the laser frequency continuously across a bandwidth and analyzing the temporal delay profiles in the frequency domain, the system achieves high sensor density while maintaining large dynamic range, as the continuous wave operation preserves optical power levels throughout the multiplexed sensor array
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 continuous and spatially resolved interrogation of multiple sensors with high sensitivity and dynamic range, minimizing phase noise and nonlinear effects, and allowing for efficient multiplexing of a large number of sensors along a single fibre.
Implementation Method 1
continuously and repeatedly frequency sweeping the interrogation light from the laser source within a sweep bandwidth, SBW, over a sweep duration, t sw , with a substantially constant sweep rate r = SBW/t sw
Implementation Method 2
detecting reflected signals being returned from the sensor array by each of the reflectors, respectively, wherein detection comprises mixing a return light signal from the array with a local oscillator, LO, signal onto an optical receiver to produce an electrical radio frequency signal
Implementation Method 3
mixing a return light signal from the array with a local oscillator, LO, signal onto an optical receiver
Implementation Method 4
an sensor array with at least a first and a second reflector and with a sensor delay being a difference in propagation time for light being reflected from the first and second reflector, respectively
Data Source
Figure 1
Figure 2a~2c
Figure 3a~3c
AI summary
The invention relates to a method of interrogating an interferometric optical fiber sensor system including a laser source configured to generate interrogation light and a sensor array with at least a first reflector and a second reflector. The method includes continuously and repeatedly frequency sweeping the interrogation light from the laser source within a sweep bandwidth (SWB) over a sweep duration (tsw) with a substantially constant sweep rate r=SBW/tsw to produce a swept interrogation light signal, launching the swept interrogation light signal into the sensor array, detecting reflected signals being returned from the sensor array by each of the reflectors, respectively, wherein detection includes mixing a return light signal from the sensor array with a local oscillator signal onto an optical receiver to produce an electrical radio frequency signal, demultiplexing the electrical radio frequency signal into a first signal channel and a second signal channel, corresponding to the first and second reflector, respectively, demodulating each of the first and second signal channel into a first phase response from the first reflector and a second phase response from the second reflector, and subtracting the first phase response from the second phase response to obtain a sensor phase signal.