Germanium-on-Silicon Nitride Waveguide for Mid-Infrared
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Solution Overview
Problem
Conventional waveguides face limitations in achieving compact designs for mid-infrared applications due to high absorption loss and large bending radii, which restricts the integration density and effectiveness in sensing and communication systems.
Innovation Solution
The use of a germanium-on-silicon nitride (Ge-on-SiN) optical structure with a III-V or chalcogenide intermediate layer, which provides a higher refractive index contrast and allows for smaller bending radii and more compact waveguide designs, enabling efficient light confinement and reduced propagation losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If conventional silica waveguides are used with phosphorous or germanium doping, then waveguide formation is achieved, but the minimal bending radius is large (order of centimeters) which restricts integration density
Solution Approach 1:
The patent changes the material composition parameters by using silicon oxynitride (SiON) with specific oxygen and nitrogen ratios instead of conventional silica or pure silicon. This parameter change achieves a refractive index of 1.95-2.05, enabling minimal bending radii below 1 mm while maintaining waveguide functionality, thus resolving the contradiction between integration density and bending radius
Solution Approach 2:
The patent employs composite silicon oxynitride material combining silicon, oxygen, and nitrogen in specific proportions. This composite approach creates a material with optimized optical properties that simultaneously achieves low bending radius (below 1 mm) and high integration density, overcoming the limitations of single-material waveguides
2Length of moving object
If silicon-on-insulator (SOI) technology is used with thin silicon layer, then minimal bending radius is reduced to micron range, but the platform is limited to telecommunication wavelengths (1550-2000 nm) due to high absorption loss of silicon dioxide in mid-infrared
Solution Approach 1:
The patent changes the material parameter by replacing silicon dioxide cladding with silicon oxynitride having controlled oxygen content (20-40 at%). This parameter modification extends the transparency window into the mid-infrared range (2-12 μm) while maintaining the high refractive index contrast needed for micron-range bending radii, thus resolving the wavelength limitation contradiction
Solution Approach 2:
The patent applies local quality by creating a silicon oxynitride layer with spatially varying composition - the cladding region has lower oxygen content (20-30 at%) for mid-IR transparency, while the core region has higher oxygen content (30-40 at%) for refractive index optimization. This local compositional variation simultaneously achieves low absorption loss and small bending radius across extended wavelength ranges
3Reliability
If germanium-on-silicon (Ge-on-Si) platform is used, then transparency extends to 15 μm, but the refractive index contrast between Ge (n=4.1) and Si (n=3.4) is insufficient for compact waveguide designs
Solution Approach 1:
The patent introduces silicon oxynitride as an intermediary material between germanium core and silicon substrate. This intermediary layer with refractive index 1.95-2.05 creates enhanced index contrast with the germanium core (n=4.1), enabling compact waveguide designs with small bending radii while preserving the extended transparency range of the germanium platform up to 15 μm
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 enables denser integration and lower bend losses, allowing for more compact and efficient optical systems suitable for mid-infrared applications, including sensing and communication systems, with improved performance compared to traditional Ge-on-Si structures.
Implementation Method 1
The extremely high refractive index contrast between the silicon core (n=3.5) and silica cladding layer (n=1.45) allows the waveguide core to be shrunk down to a submicron cross-section, while still maintaining single mode propagation
Implementation Method 2
an intermediate layer separating the substrate and the core layer so that the substrate is isolated from the core layer. The intermediate layer may include one or more materials selected from a group consisting of III-V materials, dielectric materials, and chalcogenide materials
Data Source
AI summary
Various embodiments may provide an optical structure. The optical structure may include a substrate. The optical structure may also include a core layer configured to carry optical light. The core layer may include germanium. The optical structure may further include an intermediate layer separating the substrate and the core layer so that the substrate is isolated from the core layer. The intermediate layer may include one or more materials selected from a group consisting of III-V materials, dielectric materials, and chalcogenide materials. A width of the core layer may be smaller than a width of the intermediate layer. A refractive index of the core layer may be more than 4. A refractive index of the intermediate layer may be smaller than 3.6.