RFOG Common Intensity Modulation for Kerr Bias Reduction
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Solution Overview
Problem
Resonator fiber optic gyroscopes (RFOGs) suffer from Kerr effect bias errors due to asymmetrical loss distributions and power fluctuations, which are not effectively addressed by existing methods that stabilize beam power, leading to non-reciprocal phase shifts and bias noise above navigational grade requirements.
Innovation Solution
Implementing common intensity and loss modulation techniques to balance the power and loss distributions of clockwise (CW) and counterclockwise (CCW) beams in RFOGs, using methods such as intensity modulators, polarizers, and piezoelectric transducers to adjust beam power and cavity loss, thereby equalizing modulation amplitudes and reducing Kerr effect bias instability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If differential power stabilization is used to reduce Kerr bias error, then beam power stability is improved, but asymmetry Kerr bias error remains sensitive to common intensity fluctuation and common loss change
Solution Approach 1:
The patent applies a common intensity modulation (copying the same modulation signal) to both CW and CCW beams. This copying approach ensures that both beams experience identical intensity fluctuations, which cancel out in the differential measurement, thereby eliminating sensitivity to common intensity fluctuations and common loss changes while maintaining beam power stability
Solution Approach 2:
Instead of using different stabilization approaches for CW and CCW beams (differential stabilization), the patent inverts the approach by applying the same common intensity modulation to both beams. This inversion transforms the problem from differential stabilization to common-mode rejection, effectively eliminating asymmetry Kerr bias error
2Productivity
If CW and CCW beams have different power levels, then the RFOG can operate, but non-reciprocal phase shift occurs causing bias error
Solution Approach 1:
The patent changes the power level parameter by applying common intensity modulation to both beams, transforming the power levels dynamically. This parameter change ensures that while the beams may have different absolute power levels for operation, their relative power ratio remains stable and their intensity fluctuations are correlated, eliminating non-reciprocal phase shift
Solution Approach 2:
The patent employs periodic intensity modulation at a specific frequency applied commonly to both CW and CCW beams. This periodic action creates a known modulation pattern that can be detected and used to compensate for power level differences, allowing operation with different power levels while maintaining measurement precision
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 proposed methods significantly reduce Kerr bias errors below navigational grade levels by balancing CW and CCW beam power and loss distributions, resulting in improved navigation accuracy and stability.
Implementation Method 1
The optical Kerr effect is a fundamental bias error source in an RFOG and often creates bias noise higher than navigational grade requirements. The Kerr effect is caused by the different phase shifts between the self-phase modulation (SPM) and cross-phase modulation (XPM) phenomenon.
Implementation Method 2
adding a common intensity modulation to the first optical signal emitted from the first light source, to adjust the first power level and produce an intensity modulated CW signal; adding the same common intensity modulation to the second optical signal emitted from the second light source, to adjust the second power level and produce an intensity modulated CCW signal
Implementation Method 3
piezoelectric transducers to adjust beam power and cavity loss
Data Source
AI summary
A method comprises providing an RFOG that includes a resonator in communication with a light source emitting a first signal at a first power level in a CW direction, and a light source emitting a second signal at a second power level in a CCW direction; adding a common intensity modulation to the first signal, to produce an intensity modulated CW signal; adding the same common intensity modulation to the second signal, to produce an intensity modulated CCW signal; introducing the intensity modulated CW signal into the resonator; introducing the intensity modulated CCW signal into the resonator; detecting modulated rate signals that are output from the resonator at a common intensity modulation frequency; and adjusting a power level ratio between the first and second power levels, to determine a modified power level ratio value where a Kerr effect bias instability due to an asymmetrical loss distribution is reduced or eliminated.