SiN Waveguide Structures for Compact Low-Loss Optical Gyroscopes
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Solution Overview
Problem
Fiber optical gyroscopes (FOGs) are large, expensive, and difficult to assemble due to the need for precise alignment of discrete optical components, making them unsuitable for high-volume production and prone to vibration and temperature variations.
Innovation Solution
Utilize silicon nitride (SiN) waveguides with fused silica cladding to create compact, low-loss waveguide structures for integrated photonics-based optical gyroscopes, which can be manufactured using wafer-scale processes, eliminating the need for precise alignment and enabling mass production.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If fiber optical gyroscopes use discrete optical components with precise alignment, then measurement precision is improved, but device complexity and ease of manufacture deteriorate
Solution Approach 1:
The patent merges multiple discrete optical components (waveguides, couplers, phase shifters) into a single integrated photonic chip. This integration maintains the interferometric measurement functionality while eliminating the need for precise manual alignment of separate components, thereby reducing device complexity without sacrificing measurement precision.
Solution Approach 2:
The patent replaces mechanical alignment of discrete optical components with monolithic photonic integration. The optical paths are defined by fabricated waveguide structures rather than mechanically positioned components, substituting mechanical alignment requirements with semiconductor manufacturing precision that can be achieved through standard fabrication processes.
2Measurement precision
If fiber optical gyroscopes use discrete optical components, then measurement precision is improved, but ease of manufacture and productivity worsen
Solution Approach 1:
The patent replaces manual assembly and mechanical alignment of discrete optical components with semiconductor fabrication processes. The photonic chip is manufactured using standard CMOS or similar fabrication techniques that enable wafer-scale production, dramatically improving ease of manufacture and productivity while maintaining measurement precision through integrated design.
Solution Approach 2:
The patent changes the manufacturing approach from discrete component assembly to integrated circuit fabrication. By adopting semiconductor manufacturing parameters and processes, the system achieves high-volume production capability while maintaining the optical measurement functionality and precision through carefully controlled fabrication parameters.
3Measurement precision
If fiber optical gyroscopes are constructed with long length optical fiber, then measurement precision is improved, but weight and volume increase
Solution Approach 1:
The patent transitions from three-dimensional fiber coil winding to planar photonic circuit integration. The long optical path required for precise measurement is achieved through multi-layer waveguide structures and compact routing on a flat chip, dramatically reducing the volume and weight while maintaining the effective optical path length needed for measurement precision.
Solution Approach 2:
The patent implements multi-layer waveguide structures where optical paths are nested across different vertical layers. This allows the long optical path to be folded and compacted within a small chip footprint, reducing both volume and weight while preserving the measurement precision that depends on optical path length.
4Measurement precision
If fiber optical gyroscopes use discrete optical components, then measurement precision is improved, but reliability deteriorates due to vibration and temperature sensitivity
Solution Approach 1:
The patent combines all optical components into a single rigid photonic chip structure. This integration eliminates the relative motion and misalignment that occur in discrete component systems under vibration, and maintains stable optical paths under temperature variations, thereby improving reliability while preserving measurement precision.
Solution Approach 2:
The patent inverts the approach to handling environmental disturbances. Rather than trying to compensate for vibration and temperature effects through complex control systems, the integrated photonic structure inherently rejects these disturbances through its monolithic construction, making the system naturally more reliable in harsh environments.
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 solution results in a smaller, more cost-effective optical gyroscope with performance equivalent to FOGs, immune to vibration, and suitable for high-volume production, reducing size, weight, and power consumption.
Implementation Method 1
silicon nitride (SiN) waveguides with fused silica cladding to create compact, low-loss waveguide structures
Implementation Method 2
The most common optical gyroscope is the fiber optical gyroscope (FOG) that operates based on interferometric measurements of optical phase shift due to the Sagnac effect
Data Source
AI summary
Disclosed herein are configurations and methods to produce very low loss waveguide structures, which can be single-layer or multi-layer. These waveguide structures can be used as a sensing component of a small-footprint integrated optical gyroscope. By using pure fused silica substrates as both top and bottom cladding around a SiN waveguide core, the propagation loss can be well below 0.1 db/meter. Low-loss waveguide-based gyro coils may be patterned in the shape of a spiral (circular or rectangular or any other shape), that may be distributed among one or more of vertical planes to increase the length of the optical path while avoiding the increased loss caused by intersecting waveguides in the state-of-the-art designs. Low-loss adiabatic tapers may be used for a coil formed in a single layer where an output waveguide crosses the turns of the spiraling coil.