Fiber-Optic Sensor Cross-Coupling for Temperature Stability
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Solution Overview
Problem
Fiber-optic sensors, particularly current and magnetic field sensors, are sensitive to wavelength shifts and temperature fluctuations, which affect their accuracy and reliability, especially in high-voltage environments where precise and stable measurements are required.
Innovation Solution
The introduction of a cross-coupling element, such as a non-exact half-wave retarder, is implemented in the optical path to balance wavelength-dependent shifts and temperature-dependent changes, allowing for a sensor signal that is insensitive to these variations, even without temperature stabilization of the light source.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If temperature stabilization of the light source is implemented, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The patent converts the harmful wavelength shifts caused by temperature variations into a beneficial compensation mechanism. By introducing a cross-coupling element that creates a counterbalancing signal response, the system transforms temperature-induced errors into a self-correcting measurement process, eliminating the need for active temperature stabilization while maintaining high measurement precision
Solution Approach 2:
The patent changes the operational parameters of the optical system by introducing a cross-coupling element with specific coupling coefficients. This modification alters the signal transmission characteristics to compensate for wavelength shifts, allowing the sensor to maintain accuracy across varying temperatures without requiring temperature control hardware
2Measurement precision
If wavelength stabilization is implemented through temperature control, then measurement precision is improved, but energy consumption increases
Solution Approach 1:
The patent transforms the energy-consuming wavelength stabilization problem into an energy-efficient solution by using a passive cross-coupling element. The element naturally compensates for wavelength shifts through its optical properties without requiring active temperature control, thereby eliminating continuous energy consumption while maintaining wavelength stability
Solution Approach 2:
The cross-coupling element provides self-service wavelength compensation by automatically adjusting the optical path based on the actual wavelength conditions. The system self-corrects for wavelength drifts without external intervention or energy input, making the sensor energy-efficient while maintaining measurement precision
3Reliability
If active temperature control is used, then reliability is improved, but device complexity increases
Solution Approach 1:
The patent converts reliability concerns about temperature drift into a benefit by designing a system where temperature variations are naturally compensated. The cross-coupling element creates opposing signal responses that cancel out temperature-induced wavelength shifts, improving long-term reliability without adding complex temperature control systems
Solution Approach 2:
The patent extracts and eliminates the temperature control subsystem from the overall sensor design. By removing this complex component while maintaining reliability through optical compensation, the system achieves simplicity without sacrificing long-term 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
This approach enables fiber-optic sensors to maintain accuracy and stability across varying temperature ranges and wavelength shifts, reducing the need for active temperature control of the light source and improving long-term reliability in high-voltage applications.
Implementation Method 1
The cross-coupling element, which introduces a wavelength-dependent signal response into the optical path
Implementation Method 2
Fiber-optic current sensors rely on the magneto-optic Faraday effect in an optical fiber that is coiled around the current conductor
Implementation Method 3
A preferred arrangement employs a reflector at the sensing fiber's far end so that the light coupled into the fiber performs a round trip in the fiber coil. Commonly, left and right circularly polarized light waves, which are generated from two orthogonal linearly polarized light waves by a fiber-optic phase retarder spliced to the sensing fiber and acting as quarter-wave retarder (QWR)
Implementation Method 4
The current-induced magnetic field generates a circular birefringence in the optical fiber that is proportional to the applied magnetic field
Data Source
Figure 1~2A
Figure 2B~3A
Figure 3B~4
AI summary
A fiber optic sensor (10) and related method are described, with the sensor (10) including a cross-coupling element (16) in the optical path between a polarizing element (2, 41, 55a, 24) and a sensing element (12), but separated from the sensing element itself; with the cross- coupling element (16) generating a defined cross-coupling between the two orthogonal polarization states of the fundamental mode of a polarization maintaining fiber (11) guiding light from the light source (1) to the sensing element (12) thus introducing a wavelength-dependent or temperature-dependent sensor signal shift to balance wavelength-dependent or temperature-dependent signal shifts due to other elements of the sensor, particularly signal shifts due to the wavelength dependence of the Faraday effect or the electro-optic effect constant.