Integrated Optic Wavemeter for FOG Scale Factor Stabilization
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Solution Overview
Problem
Fiber optic gyros (FOGs) face challenges in maintaining a stable scale factor across various environmental conditions due to poor wavelength stability of broadband light sources, optic feedback, and aging of optic components, leading to significant errors in rotation measurement.
Innovation Solution
The implementation of a photonic integrated circuit (PIC) based wavemeter system that measures the effective interferometric wavelength (EIW) of the broadband light source, allowing for robust scale factor stabilization even under harsh environmental conditions such as ionizing radiation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a broadband light source is used in FOG to achieve high power and short coherence length, then the rotation measurement capability is improved, but the wavelength stability deteriorates leading to scale factor errors
Solution Approach 1:
The patent applies preliminary action by measuring the effective interferometric wavelength (EIW) in advance using a wavemeter before the FOG operation. The system continuously monitors the EIW and uses this pre-measured information to calculate and apply scale factor corrections, preventing wavelength drift from causing measurement errors rather than reacting after errors occur
Solution Approach 2:
The patent implements feedback by creating a closed-loop system where the wavemeter continuously measures the EIW of the broadband light source, and this measurement feeds back to a control system that adjusts the scale factor accordingly. The feedback loop compensates for wavelength variations in real-time, maintaining accurate rotation measurements despite the inherent instability of broadband sources
2Measurement precision
If broadband light is used to suppress Kerr nonlinearity effects, then measurement accuracy is improved, but scale factor stability across environmental conditions deteriorates
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the scale factor parameter based on measured EIW variations. Instead of using a fixed scale factor, the system modifies this critical parameter in real-time according to the actual wavelength conditions, allowing the FOG to adapt to different environmental conditions while maintaining measurement precision
Solution Approach 2:
The patent replaces mechanical/environmental stability requirements with an optical measurement and computational correction system. Rather than relying on mechanically stable components that resist environmental changes, the system uses optical wavemeter measurements and digital scale factor adjustments to compensate for environmental effects on the broadband light source
3Ease of operation
If optic components are used in the FOG system to direct and detect light, then the rotation sensing function is achieved, but the effective interferometric wavelength changes due to filtering effects
Solution Approach 1:
The patent introduces an intermediary element - the wavemeter - that measures the EIW after it has passed through all the optic components (directional couplers, polarizers, fiber connections). This intermediary measurement captures the net effect of all filtering and modifies the broadband spectrum, providing an accurate EIW value that reflects the actual conditions in the rotation sensing path
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 enables a more stable scale factor in FOGs, reducing errors associated with environmental changes and component aging, thereby enhancing the accuracy of rotation measurements.
Implementation Method 1
a second optic waveguide, a segment of which is arranged in close proximity to the first optic waveguide, such that the second optic waveguide receives a portion of the optic signal from first optic waveguide through evanescent coupling along the interaction length
Implementation Method 2
The scale factor is linearly related to the 'effective interferometric wavelength' of the SLD's light, which is a weighted average of the SLD light's spectrum
Data Source
Figure 1A
Figure 1B
Figure 1C
AI summary
A system for stabilizing a scale factor associated with an optic rotation sensor comprises an optic rotation sensor that generates an optic signal in response to a rotation of the optic rotation sensor. A sensor detection system produces a rotation signal as a function of the optic signal and rotation of the optic rotation sensor. A first waveguide guides a portion of the optic signal for an interaction length, and produces a first processed optic signal. A second waveguide receives a portion of the optic signal from first waveguide through evanescent coupling, and produces a second processed optic signal. A wavemeter detector receives the optic signals and measures the effective interferometric wavelength (EIW) of the light based on the optic signals. A scale factor correction system receives the rotation signal and the EIW, and measures the correct rotation signal by processing the rotation signal and the EIW.