Sideband Heterodyne Switching for RFOGS Error Suppression
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Solution Overview
Problem
Resonator fiber optic gyroscopes (RFOGs) face challenges in suppressing both modulation imperfections and optical backscatter errors, with existing solutions either exacerbating one error while mitigating the other, and residual errors increase when using low-cost silicon photonics chips for sideband heterodyne modulation.
Innovation Solution
Implementing sideband heterodyne switching with frequency switching controllers that alternately switch the signs of modulation frequency offsets for CW and CCW optical beams, ensuring they are mostly different at any given time but averaged over time remain at proper frequencies, thereby suppressing both modulation imperfections and optical backscatter errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If common modulation is used for both CW and CCW propagating laser beams, then modulation imperfection errors are suppressed, but optical backscatter errors are exacerbated
Solution Approach 1:
The modulation process is segmented into two distinct stages: first, common modulation is applied to both CW and CCW beams to suppress modulation imperfections; second, sideband heterodyne modulation at different frequencies is applied to separate the beams in frequency domain, thereby suppressing optical backscatter errors. This segmentation allows each modulation stage to address a specific error type without exacerbating the other.
Solution Approach 2:
The solution transitions from single-frequency modulation to dual-frequency sideband heterodyne modulation, adding a frequency dimension separation. By modulating CW and CCW beams at different sideband heterodyne frequencies, the system creates frequency domain separation that suppresses optical backscatter while maintaining the benefits of common modulation for suppressing modulation imperfections.
2Object-generated harmful factors
If separated modulation at different frequencies is used for CW and CCW propagating laser beams, then optical backscatter errors are suppressed, but modulation imperfection errors are exacerbated
Solution Approach 1:
The solution merges two modulation approaches: common modulation (which suppresses modulation imperfections) and separated sideband heterodyne modulation (which suppresses optical backscatter). By combining these approaches in a hierarchical manner where common modulation is applied first and sideband heterodyne modulation is applied subsequently, the system achieves suppression of both error types simultaneously.
3Device complexity
If sideband heterodyne modulation is used with low-cost silicon photonics chips, then device complexity and cost are reduced, but residual errors due to modulation imperfections increase
Solution Approach 1:
The system implements feedback control through resonance tracking electronics that continuously monitor the resonator output and adjust the modulation parameters accordingly. This feedback mechanism compensates for residual errors introduced by low-cost silicon photonics chips, maintaining measurement precision despite the use of simpler, lower-cost modulation components.
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 residual errors due to sideband heterodyne modulation imperfections and optical backscatter, facilitating the use of low-cost silicon photonics chips while maintaining accurate rotation sensing performance.
Implementation Method 1
a plurality of heterodyne modulators perform heterodyne modulation of the first optical beam and the second optical beam at a heterodyne frequency plus a modulation frequency offset to produce a plurality of sideband optical beams at a plurality of sideband frequencies
Implementation Method 2
a resonator of a resonant fiber optic gyroscope configured to allow light to resonate therein
Implementation Method 3
a feedback control coupled to the resonator that detects the plurality of sideband optical beams transmitted out of the resonator and adjust frequencies of the plurality of optical beams based on the detected plurality of sideband optical beams
Data Source
Figure 1
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Figure 3A~3D
AI summary
Systems and methods for performing SHD switching for RFOGS are provided herein. A system includes a resonator in which light resonates; at least one laser source that produces first and second optical beams; heterodyne modulators that modulate the first and second optical beams at a heterodyne frequency plus a modulation frequency offset to produce multiple sideband optical beams, wherein the modulation frequency offset has a different sign for the first and second optical beams; a frequency switching controller that alternatingly switches the signs of the modulation frequency offset applied to the first and second optical beams, wherein the heterodyne modulation of the first and second optical beams are on average at the heterodyne frequency; at least one coupler that couples the sideband optical beams into the resonator; a feedback control that detects the sideband optical beams transmitted from the resonator and, in response, adjusts frequencies of the optical beams.