Polarizing Cavity for RFOG Reducing Polarization Errors
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Solution Overview
Problem
Polarization-induced errors in conventional fiber optic gyros, such as RFOGs, limit accuracy due to light coupling between polarization modes, exacerbated by temperature and stress variations, leading to inaccurate rotational rate measurements and drift.
Innovation Solution
A resonator fiber optic gyro with a hollow core optical fiber and a polarizing unit that recirculates light beams while selectively attenuating the undesired polarization state, minimizing cross-talk and temperature-dependent birefringence effects, using a frequency shifter to measure the rotation rate based on resonance frequency shifts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional optical fiber is used in RFOG, then light can be transmitted through the fiber, but polarization-induced errors occur due to light coupling between polarization modes
Solution Approach 1:
The patent extracts and removes the harmful second polarization mode from the system by using a polarizing unit that selectively transmits only the desired first polarization mode while attenuating or blocking the undesired second polarization mode. This prevents cross-talk between polarization modes and eliminates the harmful resonance effects that cause measurement errors.
Solution Approach 2:
The patent introduces polarization-preserving fiber sections at specific locations within the optical path, particularly at the recirculating device, to maintain the polarization state of light locally where it is most needed. This creates zones of high polarization stability that prevent mode coupling without requiring the entire fiber to have special properties.
2Stability of the object's composition
If polarization preserving fiber is used to limit cross-talk between polarization modes, then polarization stability is improved, but temperature variations cause resonance frequency shifts
Solution Approach 1:
The patent employs a feedback mechanism where the system continuously monitors the resonance frequencies of both polarization modes and dynamically adjusts the operating parameters to compensate for temperature-induced frequency shifts. This ensures that the desired polarization mode remains at the correct resonance frequency despite environmental variations.
Solution Approach 2:
The patent changes the operational parameters of the RFOG by selectively controlling which polarization mode resonates at the operating frequency. By using the polarizing unit to suppress the second polarization mode, the system can operate in a regime where temperature variations affect only the suppressed mode, leaving the measurement-based first polarization mode stable.
3Productivity
If fiber couplers are used to recirculate light in the RFOG, then light can be directed through multiple passes, but light is incidentally coupled into the second polarization mode
Solution Approach 1:
The patent introduces a polarizing unit as an intermediary component between the fiber coupler and the optical fiber coil. This polarizing unit acts as a mediator that allows the fiber coupler to perform its recirculation function while simultaneously filtering out the harmful second polarization mode that the coupler inadvertently generates.
4Measurement precision
If the RFOG system is made more complex to eliminate polarization errors, then measurement accuracy improves, but device complexity increases
Solution Approach 1:
The patent makes the polarizing unit serve multiple functions: it filters out the second polarization mode, maintains the polarization state of the first mode, and can be integrated with existing fiber coupler architectures. This multi-functionality achieves high measurement precision without proportionally increasing system complexity.
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
Significantly reduces polarization errors and temperature-dependent drift, enhancing the accuracy and stability of rotational rate measurements, achieving low bias and angle random walk, and allowing for compact, low-cost, and stable gyro designs.
Implementation Method 1
a polarizing unit configured to reflect a first polarized light component of the first and second counter-propagating light beams, pass a second polarized light component of the first and second counter-propagating light beams
Implementation Method 2
an optical fiber coil having a hollow core and first and second ends
Implementation Method 3
The resonance frequencies for each of the CW and CCW paths through the coil are based on a constructive interference of successively recirculated beams in each optical path
Implementation Method 4
A rotation of the coil produces a shift between in the respective resonance frequencies of the resonant coil and the frequency difference, such as may be measured by tuning the CW beam and CCW beam frequencies to match the resonance frequency shift of the coil due to rotation, indicates the rotation rate
Data Source
Figure 1~2
Figure 3
AI summary
Methods and apparatus are provided for attenuating polarization errors in ring resonators of fiber optic gyros. A ring resonator is provided having first and second resonance frequencies and comprising an optical fiber coil (24) having a hollow core and first and second ends, a light beam generator (12, 14, 16, 18, 20) coupled to the optical fiber coil and configured to generate first and second counter-propagating beams in the hollow core, and a light recirculator (22) coupled to the first and second ends of the optical fiber coil and configured to direct a first light beam exiting the first end of the optical fiber coil into the second end of the optical fiber coil. The first light beam is based on one of the first and second counter-propagating beams. The light recirculator comprises a first polarizing unit (23) configured to reflect a first polarized component of the first light beam and further configured to extract a second polarized component of the first light beam.