Bias-reduced Fiber Optic Gyroscope Using Polarizing Elements
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Solution Overview
Problem
Fiber optic gyroscopes face significant polarization errors due to cross-couplings in fiber splices and birefringence, which degrade the gyroscope's bias performance, especially in conventional single-mode fibers, and depolarized gyroscopes struggle to reduce these errors to required levels with existing polarizers having insufficient polarization extinction ratios.
Innovation Solution
Incorporating additional polarizing elements with high polarization extinction ratios into specific sections of the optical circuit or as the sensing coil fiber to reject unwanted polarization modes, thereby reducing polarization errors and relaxing performance requirements of other optical elements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional single-mode optical fibers are used, then cost is reduced and radiation resistance is improved, but polarization errors increase due to cross-couplings at fiber splices and birefringence disturbance
Solution Approach 1:
The patent introduces an integrated optical circuit (IOC) as an intermediary component that actively compensates for polarization errors. The IOC contains polarization control mechanisms that correct the polarization state of light waves after they traverse the single-mode fiber, thereby eliminating the harmful polarization cross-couplings while maintaining the cost benefits of using conventional fibers.
Solution Approach 2:
The patent employs dynamic parameter changes by using electro-optic or magneto-optic effects within the IOC to adjust and control the polarization state of light. By changing the refractive index or polarization orientation through applied fields, the system can compensate for polarization errors in real-time, maintaining measurement precision despite using cost-effective single-mode fibers.
2Measurement precision
If polarization-maintaining fiber is used, then polarization errors are reduced, but device complexity and cost increase
Solution Approach 1:
The patent replaces expensive polarization-maintaining fiber with a more economical approach using standard single-mode fiber combined with a relatively simple integrated optical circuit. The IOC acts as a cost-effective substitute for the complex and expensive PM fiber infrastructure, achieving the same polarization control function with lower overall system cost and reduced complexity.
Solution Approach 2:
The patent substitutes the mechanical/physical structure of polarization-maintaining fiber (which requires precise manufacturing and alignment) with an optical-based solution using the IOC. This substitution eliminates the need for complex fiber construction and splicing procedures, thereby reducing device complexity while maintaining polarization control.
3Measurement precision
If high polarization extinction ratio polarizers are used to reduce polarization errors, then measurement precision improves, but device complexity and cost increase
Solution Approach 1:
The integrated optical circuit performs multiple functions simultaneously: it acts as a polarizer, a polarization controller, and a phase modulator. By combining these functions into a single compact component, the patent achieves high polarization extinction ratio without requiring separate high-performance polarizers, thereby reducing overall device complexity while maintaining measurement precision.
Solution Approach 2:
The patent merges the polarizer function with other optical processing functions into the integrated optical circuit. This consolidation eliminates the need for separate high-extinction-ratio polarizer components and their associated alignment and mounting infrastructure, reducing device complexity while achieving the required polarization error reduction through the IOC's integrated polarization control mechanisms.
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
The use of polarizing elements significantly reduces polarization errors, improving gyroscope bias stability and allowing for more cost-effective and compact designs, particularly in depolarized fiber optic gyroscopes, by enhancing the rejection of unwanted polarization modes and minimizing cross-coupling points.
Implementation Method 1
Incorporating additional polarizing elements with high polarization extinction ratios into specific sections of the optical circuit to reject unwanted polarization modes
Implementation Method 2
Sagnac phase for rotation rate sensing is determined by measuring the intensity of interfering lightwaves traveling through an identical optical path of a fiber loop in opposite directions
Implementation Method 3
Due to cross-couplings at fiber splices and birefringence disturbance in the fiber, there is always energy exchange between the two polarization modes
Data Source
AI summary
A fiber optic gyroscope includes a light source, a coupler coupled to the light source, a photodetector coupled to the coupler, an integrated optic circuit (IOC) coupled to the coupler by a first element, and a sensing loop coupled to the IOC by second and third elements. At least one of the first, second and third elements includes a polarizing element.