Distributed Fibre Optic Sensing Using Offset Pulse Sequences
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Solution Overview
Problem
Existing distributed fibre optic sensing systems, such as DAS, are limited by the need for light pulses to be separated by a period greater than the round-trip time along the fibre, which restricts the sampling rate and sensing bandwidth.
Innovation Solution
Generating two distinguishable sequences of light pulses that are offset in time and transmitting them simultaneously into an optical fibre, allowing for increased sampling rates and higher sensing bandwidths by enabling the detection of multiple pulses at once.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If light pulses are separated by a period greater than the round-trip time along the fibre, then range ambiguity is avoided, but the sampling rate and sensing bandwidth are restricted
Solution Approach 1:
The single pulse sequence is segmented into multiple sub-sequences (first sequence, second sequence, etc.) that are transmitted simultaneously with different time offsets. Each sub-sequence operates at a lower individual sampling rate, but their combined effect achieves a higher effective sampling rate while maintaining range ambiguity avoidance for each sequence
Solution Approach 2:
The patent introduces a new dimension of time offset between multiple pulse sequences. By offsetting the start times of different pulse sequences relative to each other, the system effectively increases the sampling rate without requiring any single sequence to violate the round-trip time constraint, thus resolving the contradiction between reliability and productivity
2Reliability
If light pulses are separated by a period greater than the round-trip time along the fibre, then range ambiguity is avoided, but the sensing bandwidth is restricted
Solution Approach 1:
The sensing bandwidth limitation is addressed by segmenting the overall sensing task across multiple pulse sequences with different time offsets. Each sequence contributes to a portion of the total bandwidth, and their combination achieves a broader effective sensing bandwidth while each individual sequence maintains reliability by respecting the round-trip time constraint
Solution Approach 2:
By introducing time offset as an additional dimension, the patent enables multiple pulse sequences to operate in parallel with different temporal characteristics. This dimensional expansion allows the system to achieve higher sensing bandwidth without compromising range ambiguity avoidance, as each sequence operates independently within its own time window
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 allows for a higher sampling rate of mechanical disturbances, resulting in increased sensing bandwidth and improved detection capabilities for acoustic signals and other mechanical disturbances along the optical fibre.
Implementation Method 1
A light pulse is transmitted into the fibre from a light source end
Implementation Method 2
the reflected light received back at the light source end is isolated using an optical circulator and analysed in a detector
Implementation Method 3
the reflected light received back at the light source end is isolated using an optical circulator
Implementation Method 4
By timing the instant at which the reflected light is received at the detector, it is possible to associate the received reflected light with a point along the length of the fibre, according to the round-trip time
Implementation Method 5
Rayleigh scattering centres in the fibre reflect small percentages of a light pulse back toward the light source end of the fibre
Data Source
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AI summary
An apparatus and method for distributed fibre optic sensing. The apparatus comprises: an optical signal generator configured to generate, for transmission into an optical fibre, a first sequence of light pulses and a second sequence of light pulses, the first and second sequences of light pulses offset from one another in time; a detector configured to detect light backscattered from an optical fibre and generate a corresponding output; and a processor. The processor is configured to process the output of the detector and thereby sense mechanical disturbances along an optical fibre by distinguishing, in the detector output, first signals corresponding to pulses of the first sequence of light pulses, from second signals corresponding to pulses of the second sequence of light pulses; and identifying a mechanical disturbance in the optical fibre based on the distinguished first and the second signals.