Thin SOI Waveguide Coupling via Reference Planes
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Solution Overview
Problem
Current methods for coupling light into and out of thin, sub-micron dimensioned optical waveguides in SOI-based opto-electronic devices are limited by edge facet constraints and lack efficiency in high-volume production, particularly for silicon waveguides with dimensions around 0.5 μm width and 0.15 μm thickness.
Innovation Solution
The use of reference planes within the SOI structure, such as the interface between the silicon substrate and buried oxide layer, combined with lensing elements to achieve alignment and coupling between fibers or lasers and thin waveguides, allowing for adjustable and permanent attachment to maximize optical coupling efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If edge facet coupling is used to couple light into thin waveguides, then alignment can be achieved, but device geometry is significantly restricted and coupling efficiency is reduced
Solution Approach 1:
The patent transitions from edge facet coupling (2D planar alignment) to end facet coupling through the SOI structure (3D vertical alignment). By utilizing the third dimension (depth through the substrate), the system achieves precise alignment without constraining the top surface geometry, allowing flexible device layouts while maintaining coupling precision.
Solution Approach 2:
The SOI structure acts as an intermediary medium between the light source and the thin waveguide. The substrate and buried oxide layers provide a controlled refractive index path that guides light from the input facet through the thin waveguide, enabling precise coupling while maintaining geometric flexibility in the device layout.
2Productivity
If thin waveguides are used in SOI structures, then integration density is improved, but coupling efficiency and alignment control become more difficult
Solution Approach 1:
The patent utilizes the refractive index parameters of the SOI structure (substrate, buried oxide, and thin waveguide layers) to control light propagation. By carefully selecting and controlling these material parameters, the system achieves efficient coupling into thin waveguides while maintaining high integration density.
Solution Approach 2:
The patent replaces mechanical alignment methods (physical positioning and fixation) with optical alignment through the SOI structure. The refractive index differences and waveguide geometry automatically guide the light path, eliminating the need for complex mechanical alignment systems while maintaining precise coupling efficiency.
3Manufacturing precision
If nanotapers or inverse tapers are used with thin waveguides, then coupling can be achieved in research environments, but fabrication control and manufacturability are insufficient for high volume production
Solution Approach 1:
The patent segments the coupling system into distinct functional components: the SOI structure with its defined reference planes, the thin waveguide section, and the input/output facets. This segmentation allows each component to be manufactured and aligned independently using standard semiconductor fabrication processes, improving both precision and manufacturability for high-volume production.
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 enables high-efficiency, polarization-independent coupling for both input and output signals, facilitating the integration of lasers and fibers into thin waveguides, suitable for high-volume production of opto-electronic products with improved alignment and reduced Fresnel losses.
Implementation Method 1
a lensing arrangement utilized to provide coupling between the input device and the waveguide
Implementation Method 2
Anti-reflection (AR) coatings can be used on both the fiber termination and the waveguide facet to reduce the Fresnel losses
Implementation Method 3
a defined interface within an SOI structure (such as, for example, the interface between the silicon substrate and the overlying buried oxide (BOX) layer) is utilized as a reference plane for the coupling arrangement
Implementation Method 4
Anti-reflection (AR) coatings can be used on both the fiber termination and the waveguide facet to reduce the Fresnel losses
Data Source
AI summary
An arrangement for providing optical coupling into and out of a relatively thin silicon waveguide formed in the SOI layer of an SOI structure includes a lensing element and a defined reference surface within the SOI structure for providing optical coupling in an efficient manner. The input to the waveguide may come from an optical fiber or an optical transmitting device (laser). A similar coupling arrangement may be used between a thin silicon waveguide and an output fiber (either single mode fiber or multimode fiber).