High Confinement Waveguide on Electro-Optic Substrate
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Solution Overview
Problem
Current high confinement waveguides on electro-optic substrates face challenges in reducing device size and achieving high packing density due to large bend radii and limited optical power transfer, with existing materials not providing sufficient refractive index contrast for efficient adiabatic coupling.
Innovation Solution
The development of silicon-rich silicon nitride (SiN:Si) high confinement waveguides on lithium niobate substrates, which have a refractive index higher than the electro-optic substrate, enabling adiabatic optical power transfer and smaller bend radii through precise taper designs and material deposition techniques.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If diffused waveguides with small index delta are used on electro-optic substrates, then the waveguides can be easily fabricated, but the bend radius must be large which increases device size
Solution Approach 1:
The patent employs a composite waveguide structure consisting of multiple layers with different refractive indices: a high-index core layer (e.g., TiO2 with n≈2.4), a lower-index cladding layer (e.g., SiO2 with n≈1.45), and an electro-optic substrate (e.g., LiNbO3 with n≈2.2). This composite structure creates strong optical confinement with a high index delta (Δn>0.3), enabling tight bend radii while maintaining fabrication feasibility through standard thin-film deposition techniques
Solution Approach 2:
The patent systematically varies critical parameters including the thickness of the core layer (typically 0.5-2.0 μm), the refractive index contrast between layers, and the composition ratios of materials (e.g., TiO2/SiO2 ratios) to optimize both the confinement factor and the bend radius. By adjusting these parameters, the waveguide achieves high optical confinement while maintaining a practical minimum bend radius suitable for compact device integration
2Length of stationary object
If higher index material is used to create high confinement waveguide, then the bend radius can be reduced, but the material must be electro-optically inactive requiring adiabatic power transfer
Solution Approach 1:
The patent introduces an intermediate transition region with a gradually varying refractive index profile that mediates the optical power transfer between the high-index confinement waveguide and the electro-optically active substrate waveguide. This intermediary structure, implemented through tapered or graded-index sections, enables adiabatic coupling with minimal loss while maintaining the benefits of high confinement in the main waveguide section
Solution Approach 2:
The waveguide structure is segmented into distinct functional regions: a high-confinement section with high-index core material for tight bending, an intermediate transition section for adiabatic mode transformation, and an electro-optic active section for modulation. This segmentation allows each region to be optimized for its specific function, reducing overall device complexity despite the multiple zones required
3Manufacturing precision
If silicon-rich silicon nitride waveguide is used on lithium niobate substrate, then the refractive index contrast increases enabling smaller features, but the optical power transfer efficiency decreases
Solution Approach 1:
The patent applies local quality optimization by using silicon-rich silicon nitride (SiNx with x<2) specifically in regions where high confinement is required (e.g., bend sections and coupling regions), while maintaining optimal stoichiometric composition in sections requiring efficient electro-optic interaction. This localized material composition control maximizes the refractive index contrast (Δn>0.3) where needed while minimizing optical loss in other regions, achieving both small feature sizes and efficient power transfer
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 solution allows for reduced mode size, increased packing density, and efficient optical power transfer, enabling smaller, more integrated electro-optic devices with lower optical losses and improved modulation efficiency.
Implementation Method 1
the high confinement waveguide having a refractive index nc greater than ns such that the electro-optic substrate induces total internal refraction within the high confinement waveguide
Implementation Method 2
a refractive index nc greater than nw such that most of the optical power will couple from the optical waveguide to the high confinement waveguide when the high confinement waveguide is in contact with the optical waveguide
Data Source
AI summary
The invention relates to an optical device including a passive high confinement waveguide, such as of silicon-rich silicon nitride, on an electro-optic substrate, like lithium niobate, optically coupled to a waveguide in the electro-optic substrate. A wide range of electro-optic devices are enabled by this high confinement waveguide structure, including: directional couplers, compact tap couplers, folded electro-optic devices, electro-optic modulators including ring resonators, electro-optic gratings. Further applications enabled by the present invention include hybrid passive planar lightwave circuits (PLC) integrated with electro-optically active waveguides, using the high confinement waveguide as an intermediary waveguide to transfer optical power between the passive and active components.