Fiber-Optic Current Sensor Bias Phase Shift
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Solution Overview
Problem
Fiber-optic current sensors using passive optical components face accuracy limitations due to asymmetries in detection channels, which are insufficient for precise electricity metering, despite achieving acceptable accuracy in high voltage substation protection.
Innovation Solution
Introducing a static bias optical phase shift between two sets of light waves with opposite signs in detector channels, allowing for passive detection and normalization of optical power changes to reduce the effects of uneven intensity and loss, and incorporating temperature compensation for improved accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If passive optical components (wave-plates and polarizers) are used to detect phase shift, then device complexity is reduced, but measurement precision deteriorates due to channel asymmetries
Solution Approach 1:
A static bias optical phase shift is introduced between the two sets of light waves before detection. This preliminary phase shift causes the optical power changes in the two detector channels to be in anti-phase, enabling normalization to compensate for channel asymmetries and improve measurement precision while maintaining passive component simplicity
Solution Approach 2:
The invention changes the optical phase shift parameter by introducing a static bias phase shift between light waves. This parameter modification transforms the detection characteristic so that power changes become anti-phase in the two channels, allowing accuracy improvement through normalization without increasing device complexity
2Measurement precision
If two detection channels with opposite phase power changes are used, then measurement precision can be improved through normalization, but device complexity increases due to additional optical components and signal processing
Solution Approach 1:
The static bias phase shift mechanism serves multiple functions: it creates anti-phase power changes in the two channels for normalization, enables temperature compensation through the temperature-dependent Verdet constant, and maintains compatibility with passive optical components. This multi-functionality achieves precision improvement without proportionally increasing complexity
3Measurement precision
If temperature compensation is incorporated, then measurement precision is improved by stabilizing against temperature variations, but device complexity increases
Solution Approach 1:
The invention utilizes the temperature-dependent Verdet constant as a natural feedback mechanism. The static bias phase shift combined with the Verdet constant's temperature dependence provides inherent temperature compensation, stabilizing the measurement against temperature variations without requiring external temperature control systems or additional complex compensation mechanisms
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
Enhances the accuracy of fiber-optic current sensors by stabilizing the sensor signal against temperature variations and channel asymmetries, meeting the stringent requirements of electricity metering while maintaining protection-level accuracy.
Implementation Method 1
Fiber-optic current sensors rely on the magneto-optic Faraday effect in an optical fiber that is coiled around the current conductor. The current-induced magnetic field generates circular birefringence in the optical fiber that is proportional to the applied magnetic field.
Implementation Method 2
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 are injected into the sensing fiber 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 3
High performance current sensors often use an interferometric technique based on non-reciprocal phase modulation as also applied in fiber gyroscopes in order to measure the optical phase shift
Data Source
AI summary
A method of increasing accuracy of optical sensors based on generating two sets of light waves having different velocities in the presence of a non-vanishing measurand field within a sensing element of the sensor is described. A defined static bias phase shift is introduced between the two sets of light waves. The sensor converts a total optical phase shift including static bias optical phase shifts and measurand-induced optical phase shifts into anti-phase optical power changes in at least two detector channels. The method includes steps of normalizing the optical power changes after their conversion into electrical detector signals in the two detector channels to reduce effects of uneven intensity or power of the light source and different loss or gain in the detector channels. Further methods, sensors and apparatus for temperature stabilizing such optical sensors and novel sensors are also presented.