Fiber-Optic Gyroscope Phase Modulator Lock-In Suppression
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Solution Overview
Problem
Fiber optic gyroscopes, particularly Sagnac interferometers, face challenges in accurately measuring low yaw rates due to the lock-in effect caused by the frequency response of the phase modulator, leading to insensitivity and inaccurate readings at near-zero angular rates.
Innovation Solution
A control system for fiber optic gyroscopes that uses a phase modulator and a control unit to generate control signals based on integral values, eliminating low-frequency components and suppressing mean values, thereby reducing the lock-in effect by switching between different control signal values depending on an integral value, ensuring the phase modulator responds similarly at low and high frequencies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If phase modulation is used to set the operating point at maximum gradient for high sensitivity, then measurement sensitivity is improved, but frequency response becomes dependent on control signal frequency due to charge carrier mobility
Solution Approach 1:
The patent applies periodic square-wave modulation to switch between two different bias phases (e.g., 0 and π) of the interferometer. This periodic switching causes the phase modulator to operate at two different operating points alternately, and the evaluation unit processes the alternating measurement signals to compensate for frequency-dependent response variations, thereby maintaining measurement accuracy across different frequencies
Solution Approach 2:
The patent changes the operating parameters of the phase modulator by switching between multiple bias phases. The evaluation unit detects the frequency-dependent response characteristics at each bias phase and uses this information to compensate for the frequency response variations, ensuring consistent measurement accuracy across different modulation frequencies
2Device complexity
If integrated optical chip is used as phase modulator for compactness, then device integration is improved, but lock-in effect occurs at low yaw rates due to frequency response characteristics
Solution Approach 1:
The patent uses periodic switching between two bias phases to generate alternating measurement signals. The evaluation unit processes these alternating signals to identify and eliminate the lock-in effect that occurs at low yaw rates, thereby restoring measurement accuracy in the near-zero rotation rate range while maintaining the compact integrated optical chip structure
Solution Approach 2:
The evaluation unit analyzes the measurement signals to detect the frequency response characteristics of the integrated optical chip phase modulator. By using feedback from the detected lock-in effect, the system compensates for the measurement errors at low yaw rates, maintaining accuracy without requiring changes to the integrated optical chip structure
3Measurement precision
If control signal frequency is reduced for low yaw rate measurement, then measurement range is improved, but phase modulator response becomes less pronounced due to frequency response characteristics
Solution Approach 1:
The patent maintains a constant modulation frequency for the phase modulator while periodically switching between two bias phases. This approach keeps the phase modulator operating in its optimal frequency response range while the periodic phase switching enables detection of low yaw rates by creating measurable variations in the interference pattern, thus resolving the contradiction between measurement range and response speed
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 enables high-precision yaw rate measurements even at low yaw rates by eliminating the lock-in effect, providing accurate and reliable data without the accumulation of output signals at zero yaw rates.
Implementation Method 1
Physical effects in the MIOC, e.g. B. mobile charge carriers, cause a dependence of the phase modulation on the frequency of the control signal
Implementation Method 2
This uses the Sagnac effect, according to which, when an optical light guide loop rotates about its normal, an optical path difference occurs between two light beams traveling in opposite directions in the light guide loop
Data Source
Figure 1A~1B
Figure 2
Figure 3
AI summary
The control system (100) for a fibre-optic gyroscope comprises a phase modulator (110) for modulating a phase of a light signal (115) and a control unit (120) for producing a control signal (125), by the magnitude of which the phase is modulated and which is fed to the phase modulator. Moreover, the control system (100) comprises an integration unit (130) for determining an integral value of an integral over an input signal (127). Here, the control signal (125) assumes a first value or a second value depending on the integral value.