Fiber-Optic Gyro Quadrature Error Reduction With Harmonic Phase Control
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Solution Overview
Problem
Resonator Fiber-Optic Gyros (RFOGs) face significant errors due to quadrature errors, which are exacerbated by temperature and environmental changes, and current methods to control demodulator resonance phase introduce unacceptable side effects.
Innovation Solution
The implementation of a system with a quadrature error reducer circuit that includes an amplitude control loop and a second harmonic phase control loop, which adjusts the phase of a second harmonic modulation signal to cancel out quadrature errors without introducing a disturbance signal, using a phase sensitive demodulator and numerically controlled oscillators to generate orthogonal reference signals for in-phase and quadrature demodulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a disturbance signal is introduced to control demodulator resonance phase, then the reference phase can be controlled to zero out response to the disturbance signal, but this introduces unacceptable side effects
Solution Approach 1:
The patent extracts and separately processes the quadrature error signal from the main resonance detection signal. By using a quadrature demodulator to extract the quadrature error component and feeding it back through a phase control loop, the system controls the demodulator reference phase without introducing disturbance signals into the main sensing path, thus avoiding the harmful side effects while achieving precise phase control
Solution Approach 2:
The patent introduces a quadrature demodulator as an intermediary device that separately processes the quadrature error signal. This intermediary allows the system to control the demodulator reference phase by processing the quadrature error component independently, rather than using disturbance signals that would directly interfere with the main resonance detection signal and cause unacceptable side effects
2Device complexity
If quadrature error is not compensated, then the system is simpler, but rotation measurement accuracy deteriorates due to quadrature error leakage into in-phase demodulator channel
Solution Approach 1:
The patent implements a feedback control system where the quadrature demodulator continuously monitors the quadrature error signal, and this error signal is fed back through a phase control loop to adjust the demodulator reference phase. This feedback mechanism automatically compensates for quadrature error and prevents its leakage into the in-phase demodulator channel, thereby maintaining rotation measurement accuracy without requiring overly complex additional hardware
Solution Approach 2:
The system uses its own quadrature error signal to automatically control and adjust the demodulator reference phase. The quadrature error, rather than being an external disturbance, becomes a self-generated control signal that the system uses to correct its own phase alignment, eliminating the need for external disturbance signals or complex external control mechanisms
3Measurement precision
If CW and CCW reference phase offsets are not perfectly matched, then some quadrature error gets into rotation measurement, but perfectly matching phases is difficult to achieve
Solution Approach 1:
The patent employs feedback control where the quadrature error signals from both CW and CCW directions are processed and fed back to automatically adjust the demodulator reference phases. This feedback mechanism continuously monitors and corrects phase offset mismatches, making it unnecessary to manually achieve perfect phase matching, thereby simplifying operation while maintaining quadrature error cancellation
Solution Approach 2:
The system automatically adjusts its own CW and CCW reference phases using the quadrature error signals as self-generated control inputs. The phase control loops for both directions use their respective quadrature errors to self-correct any phase offset mismatches, eliminating the need for external intervention or complex manual calibration procedures to achieve perfect phase matching
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 effectively reduces quadrature errors, minimizing their impact on RFOG performance and allowing for the use of less expensive laser modulators, such as those in silicon photonics, while maintaining accurate rotation sensing.
Implementation Method 1
The resonance detection modulation of the laser frequency or phase produces a signal at the resonator output that is demodulated by a phase sensitive demodulator
Implementation Method 2
The amplitude control loop is used to generate a common modulation signal. An output of the amplitude control loop is coupled to a common phase modulator in the laser assembly
Implementation Method 3
The second harmonic phase control loop is used to selectively adjust a phase of a second harmonic modulation signal in the amplitude control loop at startup
Implementation Method 4
The CW OPLL is coupled to receive an output of the master laser. The CCW OPLL is coupled to receive an output of the master laser
Implementation Method 5
An RFOG senses rotation by measuring the frequency splitting of resonance frequencies of a fiber ring resonator
Data Source
AI summary
A resonance fiber-optic gyro (RFOG) with quadrature error reducer is provided. The RFOG with quadrature error reducer includes a laser assembly, a fiber resonator assembly, a resonance tracking loop and a quadrature error reducer circuit. The resonance tracking loop, coupled to an output of the finder resonator assembly, is used to generate a resonance frequency signal that is coupled to an OPLL mixer in one of a CCW OPLL or the CW OPLL of the laser assembly. The quadrature error reducer circuit includes an amplitude control loop and a second harmonic phase control loop. The amplitude control loop is used to generate a common modulation signal. An output of the amplitude control loop is coupled to a common phase modulator in the laser assembly. The second harmonic phase control loop is used to selectively adjust a phase of a second harmonic modulation signal in the amplitude control loop at startup.