RFOG Modulation Error Correction via Asymmetric Intensity Signatures
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Solution Overview
Problem
Resonator fiber optic gyros (RFOGs) face challenges in accurately detecting resonance frequencies due to modulator imperfections and backscatter errors, leading to rotation sensing errors.
Innovation Solution
The implementation of common phase/frequency modulation with independent intensity modulations for counter-propagating laser beams, where the frequencies of intensity modulations are unequal and not harmonically related, allows for modulation error correction and rejection of intensity-type backscatter errors by encoding each light beam with a unique signature.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If common phase modulation is used for both counter-propagating beams, then modulator imperfection errors are cancelled out, but intensity-type backscatter errors cannot be rejected
Solution Approach 1:
The patent segments the modulation scheme into two independent parts: common phase modulation (for error cancellation) and independent intensity modulation (for backscatter rejection). Each beam has its own intensity modulator with unique frequency, separating the functions to achieve both error cancellation and backscatter rejection simultaneously
Solution Approach 2:
The patent introduces asymmetry by giving each counter-propagating beam a different intensity modulation frequency that is not harmonically related. This asymmetric frequency assignment creates unique spectral signatures for each beam, enabling the system to distinguish and reject backscatter errors while maintaining common mode rejection of modulator imperfections
2Object-affected harmful factors
If independent intensity modulation with unequal frequencies is applied to each beam, then backscatter errors are rejected, but modulator imperfection errors are not cancelled
Solution Approach 1:
The patent merges two separate modulation schemes: common phase modulation (applied to both beams) and independent intensity modulation (applied to each beam). This combination allows the system to simultaneously achieve common mode rejection of modulator imperfections and rejection of intensity-type backscatter errors through the independent intensity modulation frequencies
3Measurement precision
If frequency modulation or phase modulation is used for resonance detection, then measurement precision is improved, but modulator imperfections and backscatter errors are introduced
Solution Approach 1:
The patent employs feedback mechanisms where the demodulated signals are processed to generate error corrections. The system continuously monitors the resonance condition and adjusts based on the demodulated intensity signals, using feedback to compensate for modulator imperfections and backscatter effects while maintaining high 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
This approach effectively eliminates rotation sensing errors caused by modulator imperfections and reduces backscatter errors, enhancing the accuracy of resonance frequency detection and rotation sensing in RFOGs.
Implementation Method 1
The resonator translates an optical frequency to an optical intensity. For example, for the reflection resonator as shown in FIG. 1, the light intensity detected by the photodetectors will be maximum when the optical frequency is away from the resonance frequency. However, when the optical frequency approaches the resonance frequency, the light intensity sharply dips to a minimum at the resonance frequency.
Implementation Method 2
The photodetector converts the intensity signal into a voltage signal.
Implementation Method 3
If the voltage signal is passed through a demodulator (phase sensitive detector), the output of the demodulator as a function of nominal optical frequency will look like that shown in section (b) of FIG. 2.
Data Source
AI summary
Systems and methods for performing modulation error correction. An example system applies common phase/frequency modulation to first and second laser beams, a first intensity modulation to the first modulated beam, and a second intensity modulation to the second modulated beam. Signals outputted are demodulated according to the frequency of the common phase/frequency modulation. Then the first of these demodulated signals is demodulated based on the frequency of the intensity modulation of the first beam, and the second of these demodulated signals is demodulated based on the frequency of the intensity modulation of the second beam. Then, rate of rotation is determined based on demodulated signals. Frequencies of the intensity modulations are unequal and not harmonically related, and intensity modulation encodes each light beam with a unique signature.