Optical Fibre Event Detection via Spatial Mode Demultiplexing
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing optical fibre networks face challenges in detecting and localizing events such as touching, bending, or squeezing without requiring additional sensors, which are costly and incompatible with legacy equipment, and current methods struggle to accurately determine the location of mechanical events along long fibre lengths.
Innovation Solution
A spatial-mode demultiplexer is used to receive and demultiplex optical signals from a multi-mode optical fibre, allowing circuitry to detect variations in one spatial mode and estimate the location of events by measuring the time difference between the detection of signals in different spatial modes, which travel at different speeds, without the need for additional hardware along the fibre.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If fibre sensors such as Bragg gratings are inserted at different locations in an optical fibre to detect events, then event detection capability is improved, but device complexity and cost increase due to addition of multiple sensors
Solution Approach 1:
The optical fibre itself is made to serve multiple functions: it acts as both the transmission medium for data and as the sensing element for detecting mechanical events. By utilizing the fibre's inherent properties (birefringence, mode coupling) rather than adding separate sensing components, the system achieves event detection without increasing device complexity or requiring multiple dedicated sensors.
Solution Approach 2:
The optical fibre network serves itself by using its own transmitted light signal to detect external events. The events (touching, bending, squeezing) cause perturbations in the fibre that modulate the transmitted optical signal, allowing the fibre to sense its own condition without requiring external sensing infrastructure.
2Measurement precision
If many sensors are used to determine the location of events along the fibre, then location accuracy is improved, but cost increases
Solution Approach 1:
Instead of using multiple sensors distributed along the fibre length (spatial dimension), the invention uses temporal dimension by measuring the time of arrival of event-induced signal perturbations at a single remote location. The location is determined by calculating the time difference of arrival (TDOA) of perturbations from different fibre sections, converting a spatial measurement problem into a temporal measurement problem.
Solution Approach 2:
The optical signal itself acts as an intermediary carrier that conveys information about events from any location along the fibre to the remote detection point. The perturbation caused by an event modulates the optical signal, which then travels through the fibre to the detection point, allowing location information to be transmitted without physical sensors at intermediate locations.
3Measurement precision
If additional sensors are added to detect events, then event detection is improved, but compatibility with legacy equipment deteriorates
Solution Approach 1:
The existing optical fibre infrastructure serves dual purposes: data transmission and event sensing. By detecting events through perturbations in the transmitted optical signal rather than through additional sensing components, the system maintains full compatibility with legacy fibres and equipment while adding sensing capability.
Solution Approach 2:
The optical communication system is made universal by enabling it to simultaneously perform data transmission and environmental sensing functions. The same optical infrastructure that carries data also detects mechanical events, eliminating the need for separate sensing hardware and ensuring compatibility with existing networks.
4Device complexity
If a single detection point is used to monitor the fibre, then device complexity is reduced, but event location accuracy deteriorates
Solution Approach 1:
The invention compensates for the single detection point limitation by introducing temporal measurement dimension. Instead of using spatial distribution of multiple detection points, the system measures the time of arrival of perturbations at the single point and uses this temporal information to calculate the spatial location of events along the fibre, effectively trading spatial complexity for temporal precision.
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 cost-effective and accurate detection and localization of events along optical fibres, including mechanical disturbances, without disrupting data transmission and can be applied to legacy fibres, providing a sensitive and inexpensive solution for monitoring fibre integrity and identifying event types.
Implementation Method 1
Signals in different spatial modes travel at different speeds along an optical fibre and this property of the different signals allows an estimation of the location of the event to be performed by detecting the time difference between the detection of the initial variation in the first spatial mode signal and the detection of the arrival of the second spatial mode signal.
Implementation Method 2
a spatial-mode demultiplexer configured to receive an optical signal transmitted through a multi-mode optical fibre and to demultiplex said received signal
Implementation Method 3
events at or near an optical fibre which cause disruption or perturbation to the fibre and/or the presence of static non-uniformities within the fibre such as bad splices may cause disruption to an optical signal transmitted along the fibre
Data Source
Figure 1~2
Figure 3
AI summary
An apparatus and method for detecting an event at or close to an optical fibre, the apparatus comprising: a spatial-mode demultiplexer configured to receive an optical signal transmitted through a multi-mode optical fibre and to demultiplex the received signal. The apparatus further comprises circuitry configured to receive and monitor signals output by the demultiplexer, and in response to detecting a variation in a first demultiplexed signal in a first spatial-mode the variation being indicative of the event, to monitor for a second demultiplexed signal in a second spatial mode. The circuitry is configured to determine a time difference between receipt of the variation in the first demultipexed signal and detection of the second demultiplexed signal and to determine a location of the event from this time difference.