Dual-Mode Fibre Optic Interrogator for Polarisation and Rayleigh Sensing
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Solution Overview
Problem
Conventional coherent Rayleigh distributed fibre optic sensing systems require separate interrogators for performing polarisation optical time domain reflectometry (POTDR) measurements and coherent Rayleigh sensing, limiting their versatility and efficiency.
Innovation Solution
A coherent Rayleigh interrogator is configured to operate in two modes: one mode with high optical power to induce non-linear effects in a first length of optical fibre, making the interrogating radiation incoherent, allowing polarisation sensing, and another mode with low optical power to maintain coherence for conventional Rayleigh sensing, enabling both polarisation and coherent sensing functionalities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a single interrogator is used for both polarisation sensing and coherent Rayleigh sensing, then device versatility is improved, but the ability to maintain coherence for Rayleigh sensing deteriorates when high power is used for polarisation sensing
Solution Approach 1:
The patent segments the optical path by introducing a first length of optical fibre upstream of the polariser that is separate from the sensing fibre. This allows the interrogator to use high power for polarisation sensing in the first fibre segment without affecting coherence in the sensing fibre segment, resolving the contradiction between versatility and coherence maintenance.
Solution Approach 2:
The first length of optical fibre acts as an intermediary element between the interrogator and the sensing fibre. It enables the high power interrogating radiation to experience non-linear effects and become incoherent before reaching the polariser, while the sensing fibre maintains coherence for Rayleigh sensing, thus mediating between the conflicting requirements.
2Measurement precision
If high optical power is used to induce non-linear effects for polarisation sensing, then polarisation sensing capability is improved, but coherence of the interrogating radiation deteriorates
Solution Approach 1:
The optical path is segmented into a first length of optical fibre for polarisation sensing and a sensing fibre for Rayleigh sensing. The high power is applied only to the first fibre segment to induce non-linear effects and destroy coherence, while the sensing fibre maintains coherence, thus resolving the contradiction between measurement precision and coherence stability.
Solution Approach 2:
The patent applies local quality by making different parts of the optical path have different functions: the first length of optical fibre is designed to experience non-linear effects and become incoherent, while the sensing fibre is designed to maintain coherence. This local differentiation allows high power polarisation sensing without compromising overall system coherence.
3Reliability
If separate interrogators are used for polarisation sensing and coherent Rayleigh sensing, then sensing reliability is improved, but device complexity increases
Solution Approach 1:
The patent merges the functionality of two separate interrogators into a single interrogator by introducing a first length of optical fibre upstream of the polariser. This single interrogator can operate in both polarisation sensing mode (high power, incoherent) and coherent Rayleigh sensing mode (low power, coherent), reducing device complexity while maintaining sensing reliability.
Solution Approach 2:
The single interrogator is designed with multi-functionality to perform both polarisation sensing and coherent Rayleigh sensing. By using the first length of optical fibre to enable incoherent high-power operation for polarisation sensing while maintaining coherent operation for Rayleigh sensing, the interrogator achieves universality without requiring separate devices.
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
Enables simultaneous polarisation optical time domain reflectometry (POTDR) measurements and coherent Rayleigh sensing using a single interrogator, enhancing the system's capability to detect dynamic and static deformations in the fibre, such as bending and twisting, while maintaining sensitivity and accuracy.
Implementation Method 1
the interrogator is configured to output coherent optical radiation with an optical power such that the interrogating radiation experiences non-linear effects when propagating in the first length of optical fibre so as to reduce coherence of the interrogating radiation
Implementation Method 2
the interrogator is configured to determine the extent of any variation in polarisation of the radiation which is Rayleigh backscattered from within the sensing fibre
Implementation Method 3
detecting radiation which is Rayleigh backscattered from within the sensing fibre
Data Source
AI summary
This application relates to distributed fibre optic sensing. A sensor apparatus includes an interrogator for repeatedly interrogating a sensing optical fibre with interrogating optical radiation and detecting radiation which is Rayleigh backscattered from within the sensing fibre. In a first, polarisation sensing mode of operation, the interrogator is optically coupled to the sensing fibre via an optical system that includes a length of optical fibre upstream of a polariser and the interrogator is configured to output coherent optical radiation with an optical power such that the interrogating radiation experiences non-linear effects when propagating in the length of optical fibre, so as to reduce coherence of the interrogating radiation. In the first mode, the interrogator determines the extent of any variation in polarisation of the backscatter radiation. The apparatus may also be operable in a second, coherent sensing mode in which the interrogator outputs optical radiation below a non-linear threshold.