Tapered Waveguide Spot Size Converter for Fiber Coupling
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Solution Overview
Problem
The existing optical spot-size converters face challenges in efficiently coupling single-mode optical fibers to silicon-based photonic integrated circuits due to mismatches in spot sizes and refractive indices, leading to high coupling losses, and conventional manufacturing methods are expensive and difficult to scale for large volume production.
Innovation Solution
A tapered-width waveguide structure with a tapered gap between two waveguide portions, allowing for gradual increase in width and decrease in distance, which reduces coupling loss and enables efficient mode field diameter expansion to match that of single-mode fibers, fabricated using CMOS-compatible deep UV lithography for cost-effective production.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If conventional single tip SSC waveguides are used to expand mode field diameter, then coupling loss is reduced, but the maximum MFD is limited to only about 3 or 4 microns which is insufficient for matching single-mode fiber
Solution Approach 1:
The waveguide is divided into multiple tips (at least two tips) instead of a single tip structure. Each tip contributes to mode field expansion, allowing the combined structure to achieve larger MFD (7 microns or more) while maintaining low coupling loss. The segmentation enables the waveguide to match both the small core of the silicon photonic circuit and the larger mode field of the single-mode fiber.
Solution Approach 2:
The invention transitions from a single-dimensional tip structure to a multi-dimensional arrangement with multiple tips spaced at specific distances. The tips are positioned with distances of 0.2-0.48 microns between them, creating a spatial distribution that expands the mode field in multiple directions simultaneously, achieving MFD of 7 microns or more.
2Manufacturing precision
If e-beam lithography is used to manufacture SSC waveguides with sub-micrometer features, then manufacturing precision is improved, but production speed decreases and cost increases making it unsuitable for large volume manufacturing
Solution Approach 1:
The invention changes the critical parameter from tip width to tip spacing. The tips can be manufactured with standard lithography resolution (0.5-1.0 micron), and the precise parameter becomes the spacing between tips (0.2-0.48 microns), which can be controlled through deposition thickness or etch depth. This parameter transformation enables compatibility with high-speed, low-cost lithography processes while maintaining the required precision for functionality.
3Area of moving object
If the distance between multiple tips is increased to expand MFD further, then mode field diameter increases, but coupling efficiency decreases due to mode field distortion
Solution Approach 1:
The invention uses a controlled amount of spacing (0.2-0.48 microns) between tips - not too close to limit MFD expansion, not too far to cause mode distortion. This partial action principle finds the optimal intermediate range that achieves sufficient MFD expansion (7 microns or more) while maintaining coupling efficiency above 80%.
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
The solution achieves coupling losses of less than 2 dB with a mode field diameter of 7 microns or more, significantly improving the efficiency and reducing manufacturing costs by eliminating the need for high-resolution lithography.
Implementation Method 1
the width of the first and second waveguide portions gradually increases toward the first end of the third waveguide portion, and a distance between the first waveguide portion and the second waveguide portion gradually decreases from a second end of the first waveguide portion to the first end of the first waveguide portion
Data Source
AI summary
A waveguide comprising: a tapered-width first waveguide portion and second waveguide portions and a third waveguide portion, such that along a first direction, widths of a first and the second waveguide portions gradually increase towards a first end of the third waveguide portion, and a distance, in a second direction, between the first waveguide portion and the second waveguide portion gradually decreases from a second end of the first waveguide portion to the first end of the first waveguide portion, wherein the second direction is perpendicular to the first direction; and the maximum distance Gmax between the second end of the first waveguide portion and a second end of the second waveguide portion is greater than 0.2 μm and less than 0.48 μm; and the waveguide has a refractive index between 2 and 4 at a 1550 nm wavelength.