RFOG Optical Heterodyning for Rotation Error Discrimination
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Solution Overview
Problem
Conventional resonator fiber-optic gyros (RFOGs) face rotation-sensing errors due to modulator imperfections such as intensity modulation and modulation distortion, which affect the accuracy of rotation rate measurement.
Innovation Solution
The RFOG system employs a reference laser and multiple laser sources with frequency offsets, optical combiners, and resonance tracking electronics to generate beat signals, allowing discrimination between rotational information and sensing errors, and uses common-cavity modulation to reduce errors associated with modulator imperfections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If modulator is used to modulate light beam frequency, then resonance frequencies can be observed, but modulator imperfections cause rotation-sensing errors
Solution Approach 1:
The patent introduces optical combiners as intermediary devices that mix the output light beams with reference laser beams. This intermediary mixing process enables the generation of beat signals that carry rotation information while allowing the system to distinguish and eliminate errors caused by modulator imperfections, thus resolving the contradiction between achieving resonance observation and avoiding measurement errors
Solution Approach 2:
The patent implements feedback through resonance tracking electronics that detect beat signals and generate control signals to adjust laser frequencies. This feedback mechanism continuously monitors and corrects for modulator imperfections, maintaining measurement reliability while enabling accurate rotation sensing through dynamic error compensation
2Measurement precision
If multiple laser sources with frequency offsets are used, then beat signals can be generated for error discrimination, but device complexity increases
Solution Approach 1:
The patent makes the optical combiners multi-functional by having them perform both the primary function of combining light beams and the additional function of generating beat signals for error discrimination. This multi-functionality allows the same hardware components to achieve error discrimination without proportionally increasing device complexity
Solution Approach 2:
The patent merges the reference laser beam path with the sensing resonator output path through optical combiners. This merging allows simultaneous generation of multiple beat signals from a single optical path, enabling error discrimination while avoiding the need for completely separate measurement systems
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 configuration effectively reduces rotation-sensing errors by distinguishing between rotational information and error signals, improving the accuracy of rotation rate measurement in RFOGs.
Implementation Method 1
a first optical combiner coupled between a first output of the sensing resonator and a first input of the resonance tracking electronics, the first optical combiner configured to beat the first output of the sensing resonator with the reference laser beam creating a first beat signal
Implementation Method 2
a second optical combiner coupled between a second output of the sensing resonator and a second input of the resonance tracking electronics, the second optical combiner configured to beat the second output of the sensing resonator with the reference laser beam creating a second beat signal
Implementation Method 3
The resonance frequencies for each of the CW and CCW paths through the coil are based on a constructive interference condition such that all light-waves having traversed the coil a different number of times interfere constructively at any point in the coil
Implementation Method 4
The two counter-propagating (e.g., CW and CCW) beams experience different pathlengths while propagating around a rotating closed optical path, and the difference in the two pathlengths is proportional to the rotational rate that is normal to the enclosed area
Data Source
AI summary
A RFOG comprises a reference laser configured to produce a reference laser beam; a first laser source configured to produce a first laser beam; a second laser source configured to produce a second laser beam; a sensing resonator coupled to the first and second laser sources such that the first and second laser beams propagate through the sensing resonator in first and second directions, respectively; resonance tracking electronics configured to generate first and second control signals that indicate when the first and second laser beams, respectively, are off resonance; first and second optical combiners configured to beat the first and second outputs of the sensing resonator with the reference laser beam creating first and second beat signals, respectively; wherein the resonance tracking electronics is configured to discriminate between at least one rotation-sensing error and the first and second outputs of the resonator based on the first and second beat signals.