Fiber Optic Gyroscope Bias Instability Reduction
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Solution Overview
Problem
Fiber optic gyroscopes face inaccuracies in evaluating polarization errors due to simplifications that ignore wavelength-dependent properties, leading to significant deviations in bias instability and polarization error modeling, particularly in depolarized systems using non-polarization maintaining single-mode fibers.
Innovation Solution
The optical circuit design for a fiber optic gyroscope incorporates a polarization maintaining delay management fiber and a depolarizer circuit with specific fiber lengths and configurations to manage polarization extinction ratio and minimize bias instability, including a broadband light source and a single-mode optical fiber loop with tailored PM fiber lengths to reduce polarization errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If simplifications are used in polarization error models (ignoring wavelength-dependent properties), then the model is easier to compute, but the accuracy of polarization error evaluation deteriorates (up to one order of magnitude of deviation)
Solution Approach 1:
The patent transforms the polarization error evaluation from the time domain to the frequency domain by introducing wavelength as a key parameter. This allows the model to capture wavelength-dependent properties (PDL, PMD, coherence function) that were previously ignored, significantly improving accuracy without requiring complex time-domain tracking of all spurious lightwaves.
2Reliability
If Lyot-type fiber depolarizers are used to mitigate polarization errors, then polarization error reduction is achieved, but device complexity increases due to additional fiber sections and splices
Solution Approach 1:
The patent divides the depolarizer into multiple fiber sections (first, second, third, and fourth optical fiber sections) with specific length relationships (x+z=w+y). This segmentation allows the system to achieve effective depolarization while managing complexity through structured design and optimized splice placement between sections.
3Device complexity
If non-polarization maintaining single-mode fiber is used in the sensing loop, then device complexity is reduced, but polarization error increases due to birefringence effects
Solution Approach 1:
The patent introduces polarization maintaining fiber sections as intermediaries between the non-PM sensing loop and the photodetector. These intermediary sections compensate for the birefringence-induced polarization errors in the SM fiber loop, allowing the system to maintain simplicity in the sensing loop while achieving reliable polarization control at the detection stage.
Data Source
AI summary
Apparatus for providing Bias-Instability reduction in Fiber Optic Gyroscopes are provided. In one embodiment, an optical circuit for a fiber optic gyroscope having a broadband light source and an optical fiber loop comprises: a PM fiber of length v; an IOC coupled to the PM fiber via a pigtail of length d1, a second pigtail with length of d2, and a third pigtail with length of d3; a splitter that splits light received from the first pigtail into a first and second beams directed to the second and third pigtails; and a depolarizer circuit coupled to said fiber loop including a first fiber section of length x, a second fiber section of length z, a third fiber section of length w and a fourth fiber section of length y; and wherein the lengths of v, x, y, d1 and d3 are proportioned to avoid regions of high bias instability.