Hyperbolic Modulation Offset Reducer for RFOG
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Solution Overview
Problem
Resonator fiber optic gyros face challenges in employing optical phase modulators with silicon photonics due to inherent nonlinearity, leading to even-harmonic distortion and potential errors from voltage modulation drive or SiP modulator voltage to phase transfer offset.
Innovation Solution
A hyperbolic modulation offset reducer circuit is introduced, which includes demodulation circuits and control loops to detect and control the relative offset between voltage and phase, using subharmonic modulation to reject backscatter and generate offset frequency signals for phase modulation in the silicon photonics chip.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If subharmonic modulation is used to overcome even-harmonic distortion in silicon photonics modulators, then even harmonic distortion requirements are met, but new sources of offset errors are introduced
Solution Approach 1:
The patent implements feedback control loops that continuously monitor the transmission signal and adjust the modulation voltage to eliminate offset errors. The system demodulates the transmission signal, detects offset components, and feeds back correction signals to the modulator, thereby maintaining accuracy despite using subharmonic modulation in silicon photonics
Solution Approach 2:
The patent introduces intermediary demodulation and detection circuits that act as mediators between the modulator and the output signal. These circuits detect offset errors by demodulating at specific frequencies and provide intermediate correction signals, enabling precise control of the modulation process while using subharmonic techniques
2Ease of operation
If voltage modulation drive or SiP modulator voltage to phase transfer offset occurs, then simple modulation is maintained, but gyro error is introduced
Solution Approach 1:
The system employs feedback control that monitors the actual phase modulation outcome and adjusts the voltage drive accordingly. By continuously detecting offset errors in the voltage-to-phase transfer function and applying corrections, the system maintains gyro accuracy without complicating the basic modulation approach
Solution Approach 2:
The patent replaces complex mechanical or manual offset adjustment mechanisms with electronic feedback control. Instead of physically adjusting modulator parameters, the system uses electronic demodulation, detection, and feedback loops to automatically compensate for offsets, maintaining operational simplicity while improving precision
3Device complexity
If silicon photonics chip technology is used to meet cost and size requirements, then integration and miniaturization are achieved, but optical phase modulator nonlinearity cannot be overcome
Solution Approach 1:
The patent integrates feedback control loops directly into the silicon photonics chip system. By monitoring the optical output and feeding back error signals to the modulator drive, the system compensates for inherent nonlinearity while maintaining the benefits of integrated silicon photonics technology
Solution Approach 2:
The system dynamically adjusts modulation parameters such as voltage amplitude, frequency, and phase based on detected output characteristics. By changing these parameters in real-time through feedback control, the system optimizes linearity performance while maintaining integration advantages of silicon photonics
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 solution effectively reduces hyperbolic modulation offset errors, improving the accuracy of resonator fiber optic gyros by controlling the relative offset between applied voltage and optical phase, thereby meeting harmonic distortion requirements and enhancing rotation sensing precision.
Implementation Method 1
an optical phase modulator is difficult to employ in silicon while meeting even-harmonic distortion requirements because of their inherent nonlinearity
Implementation Method 2
This limitation can maybe overcome with the use of subharmonic modulation, where the inherent even-function nonlinearity is used as advantage to generate phase modulation at the desired frequency
Implementation Method 3
EP 2 813 815 B1, which discloses a system and method for sideband heterodyning detection
Implementation Method 4
The reference resonator has an operating frequency that substantially tracks with an operating frequency of the gyro resonator
Implementation Method 5
The hyperbolic modulator offset control loop is configured to create a subharmonic common modulation signal and an offset from the transmission signal that is coupled to a common phase module
Data Source
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AI summary
A hyperbolic modulation offset reducer circuit for a resonator fiber optic gyro (RFOG) is provided. The circuit includes a first demodulation circuit that is configured to demodulate a received transmission signal from a resonator at twice a sideband heterodyne detection modulation frequency to reject signals due to backscatter. A slave resonance tracking loop of the circuit is coupled to an output of the first demodulation circuit. The slave resonance tracking loop is configured to create an offset frequency signal from the transmission signal that is applied to an optical phase lock loop of a RFOG. A hyperbolic modulator offset control loop is also coupled to the output of the first demodulation circuit. The hyperbolic modulator offset control loop is configured to create a subharmonic common modulation signal from the transmission signal that is coupled to a common phase module in a silicon photonics chip of the RFOG.