Silicon-SiO2 Waveguide Connection Structure for Low-Loss Coupling
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Solution Overview
Problem
The challenge lies in connecting silicon optical waveguides with single-mode fibers (SMFs) due to significant differences in mode field diameters (MFD), leading to high coupling losses and inefficiencies in light transmission.
Innovation Solution
An optical waveguide connection structure is designed with a ridge structure and patterned over-clad layer to align the centers of silicon and SiO2 waveguides, utilizing materials with specific refractive indices to minimize loss through adiabatic and butt-coupling transitions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If direct connection between silicon optical waveguide and single-mode fiber is made, then connection simplicity is improved, but coupling loss increases significantly
Solution Approach 1:
The patent introduces an intermediate structure consisting of a ridge waveguide and a mode field adapter between the silicon optical waveguide and the single-mode fiber. This intermediary structure gradually transforms the mode field diameter from the small size of the silicon waveguide to the larger size of the SMF, enabling efficient coupling while maintaining connection simplicity.
Solution Approach 2:
The patent employs parameter changes by varying the refractive index distribution and geometric dimensions along the propagation direction. The mode field adapter uses a gradually changing refractive index profile and dimensional transition to adiabatically transform the optical mode, reducing coupling loss between waveguides with different mode field diameters.
2Area of moving object
If mode field diameter of silicon waveguide is kept small for high-density integration, then integration density is improved, but connection efficiency to SMF deteriorates
Solution Approach 1:
The patent segments the connection structure into multiple functional sections: a silicon ridge waveguide section for maintaining small mode field, a mode field adapter section for gradual transformation, and a coupling section for SMF connection. This segmentation allows each section to be optimized for its specific function while working together to solve the overall coupling problem.
Solution Approach 2:
The patent addresses the mode field diameter mismatch by introducing dimensional changes in the vertical dimension through the ridge structure and in the transverse dimension through the mode field adapter. This multi-dimensional approach enables gradual mode field transformation while maintaining the compact footprint required for high-density integration.
3Loss of energy
If ridge structure and patterned over-clad layer are added to align waveguide centers, then coupling efficiency is improved, but device complexity increases
Solution Approach 1:
The patent merges the ridge waveguide structure with the mode field adapter function into a single integrated structure. The patterned over-clad layer is combined with the ridge structure to simultaneously achieve mechanical alignment and optical mode transformation, reducing the number of separate components while improving coupling efficiency.
Solution Approach 2:
The ridge structure serves multiple functions: it provides mechanical support, defines the waveguide core, creates the mode field confinement, and enables alignment with the SMF. The patterned over-clad layer similarly serves both as an alignment reference and as part of the mode transformation structure, demonstrating multi-functionality that reduces overall device complexity.
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 effectively reduces coupling loss by aligning the mode fields, ensuring high efficiency and reliability in connecting waveguides with vastly different sizes.
Implementation Method 1
utilizing materials with specific refractive indices to minimize loss through adiabatic and butt-coupling transitions
Implementation Method 2
utilizing materials with specific refractive indices to minimize loss through adiabatic and butt-coupling transitions
Implementation Method 3
The silicon thin wire waveguide is constituted by a silicon thin wire waveguide having a core made of Si and a cladding layer made of SiO2. A specific refractive index difference between a core and a clad layer of the silicon thin wire waveguide is about 40%
Data Source
AI summary
An optical waveguide connection structure which connects a silicon optical waveguide and an SiO2 optical waveguide is constituted by an under-clad layer formed on an upper surface of a support substrate; a ridge structure formed on an upper surface of the under-clad layer; a silicon core being in contact with the ridge structure; a pattern structure which is in contact with the silicon core, has a shape and a size coincident to the silicon core in a top view, and has a refractive index lower than that of the silicon core; an SiO2 core which covers the ridge structure, the pattern structure and the silicon core, and has a refractive index lower than the silicon core and higher than the under-clad-layer; and an over-clad layer which is in contact with the SiO2 core and has a refractive index lower than that of the SiO2 core.