Full-Polarization Faraday Magnetic Field Sensor Using Sagnac Interference
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Solution Overview
Problem
Traditional magnetic field sensors suffer from poor stability, low detection accuracy, and limited sensitivity due to environmental interference, mode coupling, and the need for conversion between linearly and circularly polarized light, which results in system errors and inability to measure vector magnetic fields effectively.
Innovation Solution
A full-polarization Faraday magnetic field sensor based on a Sagnac interference system with a magneto-optical crystal and a polarization controller, using independent linearly polarized light transmission and direct polarization interference detection, which improves stability and sensitivity by employing a magnetic flux aggregator and anti-reflection coatings.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional M-Z or Michelson interference structure is used, then magnetic field measurement can be achieved, but environmental stability is poor due to non-common mode interference causing phase shift and polarization instability
Solution Approach 1:
The system divides the optical path into two independent polarization channels (fast axis and slow axis) that travel through separate paths, eliminating common mode interference. Each channel is independently modulated and detected, allowing the system to reject environmental noise that affects both paths equally.
Solution Approach 2:
The patent introduces a polarization controller as an intermediary device that precisely controls the polarization state of light before it enters the magnetic field sensing region. This mediator ensures that the light maintains the correct polarization orientation throughout the measurement process, preventing polarization instability.
2Reliability
If magnetic fluid is used in F-P cavity or M-Z structure, then magnetic field sensing is possible, but stability is low because the optical fiber and magnetic fluid are sensitive to temperature
Solution Approach 1:
The patent replaces the magnetic fluid-based sensing mechanism with a magneto-optical crystal that utilizes the Faraday effect. This substitution eliminates the temperature sensitivity inherent in magnetic fluid systems, as the magneto-optical effect in crystals is much less sensitive to temperature variations.
Solution Approach 2:
The system changes the operating parameters by using circularly polarized light instead of linearly polarized light, and by operating at wavelengths where the magneto-optical crystal has optimal performance. This parameter change enables the system to achieve higher stability while maintaining measurement precision.
3Measurement precision
If magneto-optical crystal is used to improve sensitivity, then magnetic field measurement sensitivity increases, but sensor size increases failing to meet miniaturization requirements
Solution Approach 1:
The patent embeds the magneto-optical crystal within a compact housing that integrates multiple functions including the polarization controller, optical path compensation mechanisms, and detection systems. This nested arrangement allows the entire sensor to be miniaturized while maintaining the sensitivity provided by the magneto-optical crystal.
Solution Approach 2:
The system utilizes optical field dimensions (polarization state, phase, amplitude) to achieve high sensitivity without increasing physical size. By manipulating the polarization state of light and using interferometric detection, the system achieves enhanced sensitivity through optical dimensionality rather than physical expansion.
4Reliability
If quarter wave plate is used for converting linearly polarized light to circularly polarized light, then Sagnac interference can be achieved, but there are many uncontrollable errors in the conversion process
Solution Approach 1:
The patent replaces the mechanical quarter wave plate with an electronically controlled polarization controller that uses electro-optic modulators. This substitution eliminates the uncontrollable errors associated with mechanical wave plates by using electrical signals to precisely control the polarization state, enabling accurate Sagnac interference.
5Measurement precision
If linearly polarized light is transmitted on fast axis and slow axis simultaneously, then Sagnac interference is achieved, but mode coupling occurs leading to large system error and low system sensitivity
Solution Approach 1:
The system segments the optical transmission into two independent polarization channels (fast axis and slow axis) that are independently controlled and detected. This segmentation prevents mode coupling between the two axes by treating them as separate measurement channels, thereby reducing system error and improving sensitivity.
Solution Approach 2:
The patent introduces polarization controllers as intermediary devices that independently manage the polarization state of each axis. These mediators ensure that the fast axis and slow axis operate independently without coupling, preventing mode interaction that would cause system errors.
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
The solution provides high sensitivity, large dynamic range, and vector magnetic field measurement capabilities with reduced system errors, enhancing the sensor's stability and miniaturization potential.
Implementation Method 1
The third type is to use the high magneto-optical coefficient of the magneto-optical crystal. When the magnetic field is parallel to the propagation direction of light, the polarization state of the linearly polarized light propagating in the crystal is deflected.
Implementation Method 2
The linearly polarized light transmitted on the fast axis (or slow axis) of a polarization maintaining optical fiber is specially modulated using a polarization controller.
Implementation Method 3
A full-polarization Faraday magnetic field sensor based on a Sagnac interference system
Implementation Method 4
the sensitivity of the system can be effectively improved by using a magnetic flux aggregator in the magnetic field sensing unit
Implementation Method 5
employing a magnetic flux aggregator and anti-reflection coatings
Data Source
AI summary
A full-polarization Faraday magnetic field sensor based on a Sagnac interference system and a modulation method are provided. The full-polarization Faraday magnetic field sensor includes a light source, an optical fiber coupler, a polarizer, a polarization beam splitter, a polarization controller, a magnetic field sensing unit, a detector and a polarization maintaining optical fiber. An optical signal is emitted by the light source, passes through the optical fiber coupler and the polarizer in sequence, and is divided into a clockwise path and an anticlockwise path by the polarization beam splitter. Angles between fast axis directions of the two polarization maintaining optical fiber loops and a polarization direction of the polarizer are respectively clockwise 45° and anticlockwise 45°. The two polarization maintaining optical fiber loops has opposite winding directions, a same diameter, and a same number of winding turns.