Optical Waveguide Spot Size Converter with Tapered Core
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Solution Overview
Problem
Current optical waveguide devices face challenges in achieving high-efficiency coupling with optical fibers due to mismatched refractive index and mode diameters, leading to increased coupling loss, complexity, and high costs, especially in multi-channel fiber arrays.
Innovation Solution
The optical waveguide features a substrate with a high Δ core and a low Δ core separated by a reflow layer, forming a multilayer structure with a mode coupling section using a directional coupler and a mode conversion section with a tapered core structure to adjust mode diameters, reducing refractive index mismatch and end-face reflections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the mode diameter of the optical waveguide is reduced to achieve downsizing, then the device size is reduced, but the coupling loss with optical fiber increases due to mode diameter mismatch
Solution Approach 1:
The patent introduces a spot size converter as an intermediary component between the optical waveguide and optical fiber. This converter includes a first waveguide with high relative refractive index difference and a second waveguide with low relative refractive index difference, forming an intermediate structure that gradually transitions the mode diameter from the small waveguide core to the larger fiber mode field, thereby reducing coupling loss while maintaining compact device size
Solution Approach 2:
The patent employs a vertical layer structure where the first and second waveguides are stacked in different layers with a predetermined distance between them. This three-dimensional configuration allows mode coupling to occur in the vertical dimension while maintaining a compact horizontal footprint, enabling efficient mode transformation without increasing the overall device area
2Loss of energy
If a new optical waveguide with intermediate Δ is formed to enlarge mode diameter, then coupling efficiency improves, but the device complexity and manufacturing difficulty increase
Solution Approach 1:
The spot size converter is segmented into distinct functional sections: a first waveguide section with high relative refractive index difference for initial mode confinement, and a second waveguide section with low relative refractive index difference for mode expansion. This segmentation allows each section to be optimized independently while simplifying the overall manufacturing process through modular construction
Solution Approach 2:
The patent uses composite waveguide structures with different refractive index profiles - combining materials or structures with high Δ and low Δ properties in a layered configuration. This composite approach enables the spot size converter to achieve gradual mode transformation while maintaining compatibility with standard fabrication processes for each layer
3Loss of energy
If multiple waveguides are used for mode coupling, then mode diameter adjustment improves, but optical axis alignment becomes difficult and reproducibility decreases
Solution Approach 1:
The patent designs the first and second waveguides with their cores positioned at specific vertical separation distances, creating a coupled-mode region where the optical fields naturally interact. By controlling the vertical spacing and lateral positioning, the system achieves automatic optical axis alignment through mode field overlap, eliminating the need for complex post-fabrication alignment procedures
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 configuration enables low-loss, high-efficiency coupling between the optical waveguide and optical fiber, improving reproducibility and reducing coupling loss, while minimizing end-face reflections and axis divergence.
Implementation Method 1
a mode coupling section that includes a directional coupler to conduct the mode coupling of the first core and the second core between the first position and the second position
Implementation Method 2
a mode conversion section that is connected to the mode coupling section, and has a tapered core structure to adjust the mode diameter of the first core to the mode diameter of the second core
Data Source
AI summary
An optical waveguide includes a substrate in the shape of a flat plate; lower clad that is disposed on the substrate; and a core that is disposed on the lower clad and transmits light. The optical waveguide includes a first optical waveguide and a second optical waveguide. The first optical waveguide includes a first core on the lower clad, and is disposed so as to extend along a direction in which the light travels to a first position. The second optical waveguide includes a second core on the lower clad, is disposed so as to extend along a direction in which the light travels to a second position, and has a lower relative refractive index difference than the first optical waveguide. The first optical waveguide and the second optical waveguide form, between the first position and the second position, a layer structure where the first core and the second core are disposed such that the first core is positioned a predetermined distance away from the second core in a direction perpendicular to the substrate. At least either the first optical waveguide or the second optical waveguide includes a mode coupling section and a mode conversion section. The mode coupling section includes a directional coupler to conduct the mode coupling of the first core and the second core between the first position and the second position. The mode conversion section is connected to the mode coupling section, and has a tapered core structure to adjust the mode diameter of the first core to the mode diameter of the second core.