Optical Waveguide Diffraction Grating Support Structure
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Solution Overview
Problem
The challenge is to improve the efficiency of light introduction and extraction in optical waveguides using diffraction gratings, as large diffraction gratings with free-standing structures tend to bend, leading to light loss and reduced sensitivity in optical concentration measuring apparatuses.
Innovation Solution
The solution involves an optical waveguide design with a suppressing portion that limits the deformation of fine lines in the diffraction grating pattern by providing support only at specific intervals, ensuring the diffraction grating is formed with appropriate periods, thereby reducing light loss and maintaining high diffraction efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a large diffraction grating is formed in a free-standing structure to improve light coupling efficiency, then the diffraction grating size increases to match light emitting/receiving surfaces, but the fine lines bend significantly causing loss of light and reduced diffraction efficiency
Solution Approach 1:
The diffraction grating is divided into multiple independent fine lines that are each supported by separate support structures. This segmentation prevents the entire grating from bending as a single unit, while still maintaining the overall large size needed for efficient light coupling. Each fine line can be independently stabilized without compromising the diffraction grating's overall functionality.
Solution Approach 2:
Support structures are strategically positioned only at specific locations beneath certain fine lines rather than providing uniform support across the entire diffraction grating. This localized support approach prevents bending at critical regions while maintaining the free-standing structure's overall light coupling efficiency. The support density and positioning are optimized based on local bending risks and diffraction requirements.
2Productivity
If the diffraction grating is made large to correspond to light emitting surface area, then light introduction efficiency improves, but structural stability decreases causing fine line deformation
Solution Approach 1:
The large diffraction grating is segmented into multiple fine lines, each independently supported by separate support structures. This allows the overall grating to maintain a large size for efficient light introduction while each individual fine line remains stable and properly positioned. The segmentation prevents cumulative bending effects that would occur in a uniformly supported large structure.
Solution Approach 2:
Support structures act as intermediary elements between the substrate and the fine lines of the diffraction grating. These intermediaries provide localized mechanical support to prevent fine line bending while allowing the diffraction grating to maintain its intended large size and pattern. The supports mediate between the conflicting requirements of structural stability and optical performance.
3Measurement precision
If supports are provided intermittently to maintain free-standing structure, then sensitivity improves by reducing light absorption by non-measurement materials, but fine lines bend due to lack of continuous support
Solution Approach 1:
The support structure is segmented into discrete support points rather than continuous support, allowing the diffraction grating to maintain its free-standing characteristics while preventing fine line bending. The segmented supports are positioned to provide just enough stabilization to maintain fine line straightness without creating excessive light absorption paths through supporting materials.
Solution Approach 2:
Support structures are provided with locally optimized density and positioning - more supports are placed in regions where fine lines are most prone to bending, while other regions maintain the free-standing structure for maximum sensitivity. This local differentiation allows the structure to simultaneously achieve both fine line stability and high sensor sensitivity.
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 design enhances the efficiency of light introduction and extraction in optical waveguides, improving the sensitivity of the optical concentration measuring apparatus by preventing bending of fine lines and maintaining the intended diffraction grating structure.
Implementation Method 1
When a refractive index of a material that forms a structure is greater than a refractive index of a material external to the structure, light propagating through the structure proceeds therein while repeatedly undergoing total internal reflection on the boundary between the structure and the outside of the structure
Implementation Method 2
When light propagating through the structure undergoes the total internal reflection on the boundary, light extends into the outside having the smaller refractive index. This extension is referred to as an evanescent wave
Implementation Method 3
a diffraction grating is often provided between the light source and the optical waveguide and between the photodetector and the optical waveguide, so as to bend an optical axis of light
Data Source
AI summary
An optical waveguide 15 includes a substrate 19, a core layer 12, a support 20, and a suppressing portion. The core layer 12 includes a light propagating portion 10 and a diffraction grating portion 11. The diffraction grating portion 11 includes a fine line pattern formed therein. The support 20 is made from a material having a smaller refractive index than a refractive index of the core layer 12. The support 20 supports the core layer 12 with respect to the substrate 19. The suppressing portion suppresses deformation of fine lines 13 that form the fine line pattern. The support 20 is not provided in an entire region between the light propagating portion 10 and the substrate 19 in a cross-section perpendicular to a longitudinal direction of the core layer 12 at least at a position in the longitudinal direction.