Interferometric Fiber Optic Gyroscope Bias-Modulation Waveform
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Solution Overview
Problem
High accuracy Interferometric Fiber Optic Gyroscopes (IFOGs) face challenges with bias introduction due to glitch patterns from Dual Ramp modulation and lack of servoing capability in Square-wave modulation, necessitating a modulation scheme that balances accuracy and electrical isolation.
Innovation Solution
A modulation scheme for IFOGs that produces a benign glitch pattern with zero amplitude at predefined sense harmonics, allowing for servoing of V pi and reducing electrical coupling errors, similar to Square-wave modulation but with improved electrical isolation and signal level.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If Dual Ramp modulation is used, then servoing of V pi is enabled providing accurate scale factor, but odd harmonic frequency content introduces additional bias into the IFOG
Solution Approach 1:
The patent applies asymmetry by using a square-wave modulation scheme that is inherently asymmetric in its harmonic content, producing primarily even harmonics while suppressing odd harmonics. This asymmetric spectral distribution allows the system to maintain servoing capability while eliminating the harmful odd harmonic content that causes bias errors.
Solution Approach 2:
The patent converts the typically harmful glitch pattern into a beneficial one by demonstrating that square-wave modulation's glitch pattern, while present, contains primarily even harmonics that the IFOG is immune to. This transforms what could be a harmful artifact into a benign feature that does not degrade measurement accuracy.
2Object-generated harmful factors
If Square-wave modulation is used, then glitch pattern is benign with primarily even harmonic content that IFOG is immune to, but servoing of V pi is not provided
Solution Approach 1:
The patent applies universality by designing a square-wave modulation scheme that simultaneously provides both benign glitch characteristics and V pi servoing capability. The modulation scheme is made multi-functional, serving both as a clean signal source and as a means for accurate scale factor determination through servoing.
Solution Approach 2:
The patent applies parameter changes by modifying the square-wave modulation parameters (amplitude, frequency, duty cycle) to enable V pi servoing while maintaining the benign even-harmonic spectral distribution. By adjusting these parameters, the system achieves both goals: clean glitch pattern and accurate servoing.
3Object-generated harmful factors
If Dual Ramp modulation is used with certain modulation depths, then Eigen-frequency first harmonic content is reduced, but signal level becomes nine times lower than Square-wave modulation
Solution Approach 1:
The patent applies parameter changes by optimizing the square-wave modulation depth and amplitude parameters to achieve high signal level while maintaining benign harmonic content. By carefully selecting these parameters, the system obtains nine times higher signal level compared to Dual Ramp modulation while keeping the harmful harmonic content suppressed through the square-wave's inherent spectral characteristics.
Data Source
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AI summary
An Interferometric Fiber Optic Gyro (IFOG) device for high accuracy sensing. An example IFOG includes an integrated optics chip (IOC) and a modulation component that modulates one or more light signals passing thru the IOC according to a bias-modulation waveform. A glitch pattern experienced at front-end components of the IFOG includes frequency content that has approximately zero amplitude at predefined sense harmonics. Frequency content of the bias-modulation waveform is below a predefined threshold value at the predefined sense harmonics.