SiN to TFLN Waveguide Transition via Protruding Substrate
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Solution Overview
Problem
Optical waveguide devices face challenges in achieving low-loss optical transitions between silicon nitride (SiN) and rib-type lithium niobate (TFLN) waveguides due to differences in refractive indices, leading to increased optical loss and manufacturing complexity.
Innovation Solution
An optical waveguide device with a protruding portion on the TFLN substrate, where the thickness of the protruding portion is thinner than the TFLN waveguide, and the SiN waveguide width is widened at the boundary, reducing optical loss by enhancing optical confinement and minimizing scattering.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a SiN waveguide is formed on a TFLN substrate to achieve phase modulation and optical confinement, then optical modulation performance is improved, but optical loss increases due to refractive index differences and weak optical confinement
Solution Approach 1:
The patent applies local quality by creating a protruding portion at the boundary region between the SiN waveguide and TFLN substrate. This protruding portion has different thickness characteristics compared to the surrounding areas, locally enhancing optical confinement at the critical interface where light transitions between different refractive index materials, thereby reducing optical loss without affecting the overall modulation performance
Solution Approach 2:
The patent introduces a vertical dimension solution by forming a protruding portion that extends in the thickness direction at the boundary region. This three-dimensional structural modification creates an additional optical confinement mechanism through the vertical height difference, effectively controlling light propagation at the interface between SiN and TFLN substrates with different refractive indices
2Reliability
If the SiN waveguide dimension is increased to enhance optical confinement, then optical confinement effect is improved, but the device size increases and manufacturing complexity increases
Solution Approach 1:
Instead of uniformly increasing the entire waveguide dimension, the patent applies local quality by concentrating the dimensional modification at the specific boundary region where the SiN waveguide meets the TFLN substrate. The protruding portion creates localized optical confinement enhancement only where needed for mode coupling, keeping the overall device footprint compact
Solution Approach 2:
The patent resolves the size conflict by utilizing the vertical dimension through the protruding portion's thickness variation. This allows optical confinement enhancement without proportionally increasing the horizontal waveguide dimensions, effectively decoupling the confinement effect from the overall device area
3Loss of energy
If a protruding portion is formed in the TFLN substrate at the boundary to reduce optical loss, then optical transition loss is reduced, but manufacturing precision requirements increase
Solution Approach 1:
The patent applies parameter changes by systematically controlling the thickness parameter of the protruding portion. By optimizing the thickness value within a specific range (e.g., 0.1-1.0 μm), the design achieves effective optical confinement enhancement while remaining compatible with standard fabrication processes, balancing performance improvement with manufacturability
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 enables low-loss optical transitions between SiN and TFLN waveguides, even with reduced refractive index differences, improving manufacturing efficiency and reducing optical loss.
Implementation Method 1
enhancing optical confinement and minimizing scattering
Implementation Method 2
differences in refractive indices
Implementation Method 3
a rib type optical waveguide which is a second optical waveguide and which is formed of a material having an electro-optic effect
Data Source
AI summary
An optical waveguide device includes a first substrate including a first optical waveguide and a low refractive index layer covering the first optical waveguide and being formed of a material having a lower refractive index than a refractive index of the first optical waveguide, and a second substrate joined to the first substrate and including a rib type optical waveguide which is a second optical waveguide and is formed of a material having an electro-optic effect, in which the first optical waveguide and the second optical waveguide have parts optically coupled to each other, and in plan view of the optical waveguide device, a protruding portion is formed in the second substrate in a boundary portion where the first optical waveguide overlaps with the second substrate, and a thickness of the second substrate in the protruding portion is set to be thinner than a thickness of the second substrate in the second optical waveguide.