Multilayer Nitride Waveguide Structure for Low-Loss PIC Coupling
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Solution Overview
Problem
Photonic integrated circuits (PICs) face high propagation losses in waveguides, especially between nitride waveguides and single-mode optical fibers, which are not adequately reduced by existing larger waveguides, and are sensitive to fabrication variations.
Innovation Solution
The implementation of an enlarged multilayer nitride waveguide with a cladding layer of lower refractive index than the nitride body, positioned in an inter-level dielectric layer, which allows for improved propagation losses and reduced sensitivity to fabrication variations, enabling monolithic integration with silicon waveguides and CMOS devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the waveguide size is increased to reduce propagation losses, then the propagation losses are reduced, but the integration density and compatibility with standard CMOS processes deteriorate
Solution Approach 1:
The patent extends the waveguide vertically into the buried insulator layer of the SOI substrate, utilizing the third dimension (depth) to increase the effective waveguide cross-sectional area. This vertical extension allows larger mode confinement volume without increasing lateral dimensions, thereby reducing propagation losses while maintaining planar integration density and CMOS compatibility.
Solution Approach 2:
The waveguide structure is nested within the existing SOI substrate architecture, with the nitride waveguide layer embedded in the buried insulator layer. This nesting approach allows the waveguide to utilize the existing substrate structure, achieving enhanced optical confinement without adding external complexity to the integrated circuit platform.
2Reliability
If the waveguide size is increased to improve optical coupling, then the optical coupling is improved, but the fabrication precision requirements increase
Solution Approach 1:
The patent changes the refractive index parameter by introducing a cladding layer with lower refractive index than the nitride body. This parameter change enhances the optical confinement and mode matching between waveguides and fibers, improving optical coupling efficiency. The refractive index contrast is achieved through material selection rather than dimensional precision, reducing fabrication complexity.
3Loss of energy
If a cladding layer with lower refractive index is added to the nitride waveguide, then the propagation losses are reduced, but the device structure complexity increases
Solution Approach 1:
The cladding layer is merged with the existing buried insulator layer of the SOI substrate. By combining the cladding function with the existing substrate structure, the patent reduces propagation losses through enhanced optical confinement without significantly increasing structural complexity. The cladding layer becomes an integrated part of the substrate architecture rather than an separate component.
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 reduces propagation losses, allows for changing mode shapes within the waveguide, and enables shorter directional coupling, resulting in ultra-low-loss nitride devices and photonic integrated circuits that can handle higher optical power with improved fabrication tolerance.
Implementation Method 1
a first cladding layer on at least a lower surface of the first nitride body, wherein the first cladding layer has a lower refractive index than the first nitride body
Data Source
AI summary
Structures and methods implement an enlarged multilayer nitride waveguide. The structure may include an inter-level dielectric (ILD) layer over a substrate. A first enlarged multilayer nitride waveguide is positioned in the ILD layer in a region of the substrate. A second multilayer nitride waveguide may also be provided in the ILD layer. A lower cladding layer defines a lower surface of the nitride waveguide(s). The lower cladding layer has a lower refractive index than the nitride waveguide(s). Additional lower refractive index cladding layers can be provided on the upper surface and/or sidewalls of the nitride waveguide(s). The enlarged nitride waveguide may be implemented with other conventional silicon and nitride waveguides.