Resonant Fiber Optic Gyroscope Beat Note Detection
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Solution Overview
Problem
Resonant fiber optic gyroscopes (RFOGs) face bias errors due to temperature fluctuations and time-varying electrical phenomena, which affect the accuracy of rotation sensing by introducing frequency differences in clockwise and counter-clockwise optical signals measured proximate to optical sources and the resonator.
Innovation Solution
A resonant fiber optic gyroscope with a beat note pickoff system that samples optical signals proximate to the optical resonator and uses a digital phase lock loop to detect the beat frequency, even in the presence of other frequency components, thereby reducing bias errors from temperature and electrical sources.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If frequency measurements are made proximate to the optical sources, then the measurement setup is simpler, but bias error increases due to temperature fluctuations and electrical phenomena
Solution Approach 1:
The patent introduces an optical fiber intermediary that physically connects the measurement point at the resonator to the electronic measurement equipment. This intermediary allows the optical signal to be transported from the temperature-stable resonator environment to the measurement equipment, effectively decoupling the measurement location from the sensitive optical components and eliminating temperature-induced frequency shifts in the measurement path.
Solution Approach 2:
Instead of measuring frequency directly at the optical source where temperature variations cause errors, the patent inverts the measurement approach by measuring at the resonator output where the Sagnac effect signature is already encoded. This inversion moves the measurement point away from the problematic thermal environment of the laser sources to the more stable resonator output environment.
2Measurement precision
If frequency measurements are made proximate to the optical resonator, then bias error from temperature and electrical phenomena is reduced, but additional optical components and complexity are required
Solution Approach 1:
The patent implements a multi-functional optical processing system that simultaneously performs multiple operations: it processes both clockwise and counter-clockwise optical signals, extracts Sagnac effect signatures, and provides temperature compensation all through a unified optical pathway. This multi-functionality reduces the need for separate dedicated components for each function, thereby limiting the increase in overall system complexity.
Solution Approach 2:
The patent merges the measurement of clockwise and counter-clockwise signal frequencies into a single integrated optical processing pathway at the resonator output. By combining these measurements and processing them together through the same optical fiber and detection system, the patent eliminates the need for separate measurement paths, thereby reducing the complexity increase that would otherwise result from dual independent measurement systems.
3Volume of moving object
If optical fibers are used to couple optical sources to the resonator, then the system is more compact, but temperature variations cause frequency shifts
Solution Approach 1:
The patent introduces a dedicated optical fiber intermediary specifically for signal transport from the resonator to the measurement equipment. This intermediary fiber is positioned in a thermally stable environment and serves solely as a transmission medium, isolating the measurement process from temperature variations in the coupling fibers and maintaining frequency stability while preserving system compactness.
Solution Approach 2:
The patent extracts the frequency measurement function from the temperature-sensitive optical coupling fibers and relocates it to the temperature-stable resonator output environment. By taking out the measurement operation from the problematic thermal zone of the coupling fibers and performing it at the resonator where temperatures are more stable, the patent eliminates temperature-induced frequency shifts while maintaining the compact fiber-coupled architecture.
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 enhances the accuracy of rotation sensing by minimizing bias errors from temperature fluctuations and electrical phenomena, allowing for precise measurement of rotation rates with improved sensitivity.
Implementation Method 1
Resonance frequencies are measured with optical signals respectively from optical sources generating clockwise and counter clockwise optical signals
Implementation Method 2
Rotation in RFOGs is determined by a difference of clockwise and counter clockwise resonance frequencies of a fiber ring resonator
Implementation Method 3
Varying temperatures of the optical fibers coupling the optical sources to the optical resonator can change the frequencies of the clockwise and counter clockwise optical signals propagating through the optical fibers. This arises due to time varying indices of refraction
Implementation Method 4
A method of detecting a beat note in a resonant fiber optic gyroscope... uses a digital phase lock loop to detect the beat frequency
Data Source
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AI summary
A method comprises receiving a first optical signal and a second optical signal at or near an optical resonator, where the first optical signal includes a clockwise (CW) optical signal and the second optical signal includes a counter clockwise optical signal; injecting the first optical signal and the second optical signal into a resonator loop closure optics system of the optical resonator; sampling a portion of the first optical signal and a portion of the second optical signal; combining the portion of the first optical signal and the second optical signal; converting the combined optical signals to an analog electrical signal; digitizing the analog electrical signal; storing an estimated frequency of a beat signal created by a combination of the CW optical signal and the CCW optical signal; and using the stored estimated beat signal frequency, digitally phase lock to a frequency of the beat signal.