Inverse Taper Ridge Waveguide for Fiber Coupling
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Solution Overview
Problem
The integration of photonic integrated circuits (PICs) with optical fibers is challenging due to the mismatch in mode sizes between the PIC waveguides and standard single-mode fibers, and existing edge coupling devices face limitations in mode size and integration with other photonic components.
Innovation Solution
The method involves forming a trench over an inversely tapered silicon waveguide, depositing high-index material within the trench to create a ridge waveguide, and patterning it to achieve a larger mode size compatible with fibers, allowing for monolithic integration with other photonic components while maintaining low coupling loss and improved fabrication tolerance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the mode size of the waveguide on the PIC is reduced to match the fiber mode size, then coupling compatibility with fibers is improved, but alignment tolerance deteriorates and packaging becomes challenging
Solution Approach 1:
The patent introduces a vertical dimension by creating an inverse taper structure where the waveguide width increases from bottom to top, and adds a third dimension by depositing high-index material to form a ridge structure. This multi-dimensional approach transforms the mode profile to achieve larger mode size at the output face while maintaining compatibility with the sub-wavelength thick waveguide core, thereby improving fiber coupling compatibility without sacrificing alignment tolerance.
Solution Approach 2:
The patent changes the geometric parameters of the waveguide by implementing an inverse taper profile where the width varies along the propagation direction. Additionally, it changes the refractive index parameter by depositing high-index material (such as silicon nitride or titanium dioxide) to form a ridge structure, which modifies the mode confinement and expands the mode size at the output interface to match fiber mode fields.
2Adaptability or versatility
If lenses are used to reduce the mode size of the fiber to match the waveguide mode size, then mode size matching is improved, but packaging complexity increases due to limited alignment tolerance
Solution Approach 1:
The patent extracts the mode size transformation function from external optical components (lenses) and integrates it directly into the waveguide structure through the inverse taper and ridge configuration. This eliminates the need for separate lens components and their associated packaging requirements, thereby reducing packaging complexity while achieving the same mode size matching objective.
Solution Approach 2:
The patent merges the mode size transformation function with the waveguide structure itself by creating an inverse taper profile and adding a ridge structure. This integration combines the waveguide's light-guiding function with the mode expansion function that would traditionally require separate optical components, thereby simplifying the overall device architecture and packaging.
3Adaptability or versatility
If a mode converter is used to enlarge the mode size of the waveguide for edge coupling, then fiber coupling compatibility is improved, but integration with other photonic components becomes difficult
Solution Approach 1:
The inverse taper ridge waveguide structure serves multiple functions: it guides light through the photonic circuit, transforms the mode size from sub-wavelength at the input to larger at the output for fiber coupling compatibility, and can be integrated with other standard photonic components. This multi-functional design eliminates the need for separate mode converters while achieving fiber coupling compatibility.
Solution Approach 2:
The waveguide structure is segmented into different regions with varying widths along the propagation direction, creating the inverse taper profile. This segmentation allows the structure to perform different functions at different locations: tight confinement in the sub-wavelength region for integration compatibility and expanded mode at the output region for fiber coupling, thereby achieving both objectives simultaneously.
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 results in a larger mode size (3 to 5 µm) with low coupling loss, improved reliability, and the ability to integrate with other passive and active components, enhancing the compatibility and performance of edge coupling devices.
Implementation Method 1
depositing a material having a refractive index greater than silicon dioxide over remaining portions of the cladding material and in the trench
Data Source
Figure 1
Figure 2~3B
Figure 3C~3D
AI summary
A method of fabricating an edge coupling device and an edge coupling device are provided. The method includes removing a portion of cladding material to form a trench over an inversely tapered silicon waveguide, depositing a material having a refractive index greater than silicon dioxide over remaining portions of the cladding material and in the trench, and removing a portion of the material within the trench to form a ridge waveguide.