Fiber Optic Gyroscope Coherent Coupling Reduction
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Solution Overview
Problem
Fiber-optic gyroscope systems with multiple integrated optical circuits on a single substrate face issues of spurious couplings between interferometers, leading to unstable bias defects and limited time stability due to coherent coupling, which are difficult to eliminate with existing notch-based solutions.
Innovation Solution
Introducing an optical length difference between the transmission paths of different Sagnac ring interferometers, ensuring the difference is higher than the maximum product of the group birefringence index difference and coil length, effectively reducing coherent spurious couplings by exceeding the coherence length of the source, thereby minimizing interference between interferometers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If multiple integrated optical circuits are placed on a single substrate to reduce device complexity and improve compactness, then device complexity is reduced, but spurious couplings between interferometers occur leading to unstable bias defects
Solution Approach 1:
The patent divides the optical paths into separate segments by introducing optical length differences between the transmission paths of different interferometers. This segmentation prevents coherent coupling between multiple interferometers on the same substrate by ensuring that spurious signals do not interfere constructively, thus maintaining time stability while preserving device compactness.
Solution Approach 2:
The patent introduces optical length difference as an intermediary parameter to mediate between the interferometers. By controlling the optical path length differences to exceed the coherence length of the source, the system prevents direct coherent coupling between interferometers while allowing them to function independently on the same substrate.
2Reliability
If optical length difference between interferometers is increased to reduce coherent spurious couplings, then time stability is improved, but device complexity increases
Solution Approach 1:
The patent changes the optical path length parameter to resolve the contradiction. By setting the optical length difference between interferometers to exceed the coherence length of the light source, the system eliminates coherent spurious couplings and improves time stability. This parameter change is implemented through simple optical path adjustments rather than complex structural modifications.
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 significantly reduces coherent spurious couplings, enhancing the time stability of fiber-optic gyroscope systems by ensuring that the optical length difference between interferometers is substantial enough to prevent interference, thereby maintaining long-term bias quality and increasing system compactness.
Implementation Method 1
first optical transmission means of optical length λ1 adapted to transmit the first split source beam and second optical transmission means of optical length λ2 adapted to transmit the second split source beam
Implementation Method 2
produce interferences that depend on the phase shift of the beams during their recombination
Implementation Method 3
the rotation of a Sagnac ring interferometer, with respect to an axis perpendicular to the surface of the ring, induces a phase-shift proportional to the rotational speed Ω. From this property, called the Sagnac effect, follows the main application of a Sagnac ring interferometer to a gyroscope for measuring a rotational speed
Implementation Method 4
a single-mode spatial and polarisation filter at the common input-output of the interferometer
Implementation Method 5
The two secondary beams, polarised linearly at the input, propagate in opposite directions along a closed optical path
Data Source
AI summary
A fiber optic interferometric measurement system includes a light source; first and second optical transmission elements; first and second Sagnac-ring interferometers, respectively, including first and second fiber optic coils, and, respectively, having lengths L1 and L2; and first and second individual integrated optical circuits, respectively, connected to the first and second optical transmission elements, and to the two ends of the first and second optic coils, respectively. The interferometric system includes a multiple integrated optical circuit integrating, on a single substrate, the first and second individual integrated optical circuits, and the difference Δl between the optical length of the first optical transmission elements and the optical length of the second optical transmission elements is higher than the maximum of ΔNb1×L1 and ΔNB2×L2, in which ΔNb1 and ΔNb2, respectively, are the group birefringence index difference of the first and second fiber optic coils, respectively.