RFOG Beat Note Detection for Low-Noise Bias Error Correction
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Solution Overview
Problem
Resonant fiber optic gyroscopes (RFOGs) suffer from bias errors due to time varying optical pathlengths and electrical phenomena, which affect the accuracy of rotation sensing, and existing solutions like phase locked loops are complex and prone to noise.
Innovation Solution
A method and apparatus that generate a beat note correction signal by digitizing and filtering optical signals from clockwise and counterclockwise paths, using sine and cosine functions to reduce bias errors, and differentiate the phase signal to correct for frequency differences.
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 errors increase due to time varying optical pathlengths
Solution Approach 1:
The patent introduces an intermediary measurement point located between the optical sources and the optical resonator. This intermediary pickoff point serves as a mediator that captures optical signals after they have traversed a controlled portion of the optical path, thereby reducing the impact of time-varying pathlength fluctuations while maintaining a practical measurement configuration.
2Measurement precision
If the pickoff point is moved closer to the resonator input to reduce bias error, then rotation sensing accuracy improves, but the measurement becomes more challenging to implement
Solution Approach 1:
Instead of placing the pickoff point exactly at the resonator input (excessive action), the patent uses a partial approach by positioning it at an intermediate location along the optical path. This partial measurement point provides sufficient reduction of pathlength fluctuation effects while remaining practically implementable and avoiding the complexity of exact resonator input coupling.
3Measurement precision
If additional electrical filtering and processing circuits are added to reduce bias error, then measurement accuracy improves, but device complexity and noise increase
Solution Approach 1:
The patent extracts and removes the problematic time-varying pathlength component from the measurement by using the intermediary pickoff point to obtain a reference signal that is less affected by these fluctuations. This extraction approach eliminates the need for complex electrical filtering and processing circuits that would otherwise be required to correct bias errors, thereby reducing overall device complexity and associated noise.
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 reduces bias errors in RFOGs by accurately determining the difference in resonant frequencies, enhancing rotation sensing accuracy with less complexity and noise.
Implementation Method 1
Resonant fiber optic gyroscopes (RFOGs) have better signal to noise sensitivity for rotation sensing... Rotation in RFOGs is determined by a difference of clockwise and counterclockwise resonance frequencies of a fiber ring resonator
Implementation Method 2
receiving a beat note electrical signal derived from a portion of the clockwise optical signal and a portion of the counterclockwise optical signal
Data Source
AI summary
Lower noise and complexity techniques are disclosed for compensating for time varying phase changes in fiber optics in a resonant fiber optic gyroscope (RFOG). Orthogonal components derived from an electrical beat note signal and a difference between clockwise and counterclockwise resonant frequencies of an optical resonator coil of the RFOG are determined. The orthogonal products are converted to a phase which is differentiated with respect to time to obtain a beat note correction signal.