Stacked Waveguide Optical Coupler for Silicon Photonics
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Solution Overview
Problem
High integration scale silicon photonic systems on chip (PSoCs) face significant optical losses due to mismatched beam spot sizes between silicon waveguides and III-V dies, leading to high coupling losses and alignment challenges, which are not adequately addressed by existing spot size converter (SSC) designs, especially in applications requiring multiple couplers and complex multi-channel transceivers.
Innovation Solution
An optical coupler design featuring first and second waveguide elements in adjacent layers, with the first waveguide element extending from one end of the coupler towards the other and the second waveguide element extending in the opposite direction, allowing overlap to adapt light between the two, thereby enabling efficient coupling through evanescent coupling, and utilizing materials like silicon nitride for the second waveguide to match the numerical aperture of the light source.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If conventional spot size converter designs are used to couple light between silicon waveguides and III-V dies, then coupling between the components is achieved, but coupling losses are high and alignment tolerances are stringent
Solution Approach 1:
The patent introduces a vertical dimension by stacking two waveguide layers (first waveguide layer and second waveguide layer) on top of each other. The first waveguide element extends in a first direction while the second waveguide element extends in a second direction perpendicular to the first direction, creating a three-dimensional overlapping structure that enables coupling between mismatched beam spots through evanescent field interaction in the vertical dimension.
Solution Approach 2:
The patent embeds the second waveguide element within the vertical space occupied by the first waveguide element. The second waveguide element is positioned in the vertical dimension such that its evanescent field overlaps with the first waveguide element, creating a nested configuration where one waveguide structure is effectively embedded within the field distribution of the other.
2Productivity
If the beam spot size of silicon waveguide is reduced to achieve high integration, then integration density increases, but coupling efficiency with III-V dies deteriorates
Solution Approach 1:
By utilizing the vertical dimension with stacked waveguide layers, the patent enables mode field adaptation without requiring lateral expansion of the waveguide footprint. The first waveguide element maintains a small lateral footprint for high integration density while the vertical stacking provides additional mode field area for efficient coupling with III-V dies.
Solution Approach 2:
The patent changes the refractive index parameter by introducing a second waveguide element with different material composition (e.g., silicon nitride or other high-index materials) in the vertical layer. This refractive index contrast enables effective evanescent field coupling and mode field transformation between the small-mode silicon waveguide and the larger-mode III-V die.
3Adaptability or versatility
If multiple couplers are integrated in high integration scale PSoCs, then functionality increases, but total optical losses accumulate
Solution Approach 1:
The vertical stacking architecture enables multiple couplers to be integrated in the vertical dimension rather than consuming lateral chip area. This three-dimensional integration approach allows multiple optical coupling functions to coexist with minimal lateral footprint, reducing the cumulative loss impact by enabling more efficient individual coupler designs.
Solution Approach 2:
The patent combines the coupling function of multiple waveguide elements into a single integrated structure where the first and second waveguide elements work together as a unified coupling mechanism. This merged structure achieves the coupling function with reduced loss compared to conventional separate coupler designs.
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 proposed optical coupler design significantly reduces coupling losses and alignment tolerances, enabling miniaturization of SSCs to a few tens of micrometers, enhancing bandwidth density and manufacturing efficiency while maintaining performance, particularly suitable for high integration scale PSoCs integrating SOAs and lasers.
Implementation Method 1
the first waveguide element overlaps with the second waveguide element to adapt light passing between the first end of the first waveguide element and first end of the second waveguide element
Data Source
Figure 1~2
Figure 3a~3b
Figure 3c~3d
AI summary
An optical coupler (40; 50) comprises a substrate (41). A first waveguide element (45) is provided in a first layer with respect to the substrate, wherein the first waveguide element (45) comprises a first end (45a) and a second end (45b), and wherein the first end (45a) of the first waveguide element (45) is coupled to input/output light to/from a first end of the optical coupler. A second waveguide element (43) is provided in a second layer, the second layer arranged adjacent to the first layer, wherein the second waveguide element (43) comprises a first end (43a) and a second end (43b), and wherein the first end (43a) of the second waveguide element (43) is coupled to input/output light to/from a second end of the optical coupler. The first waveguide element (45) is configured to extend from the first end of the optical coupler towards the second end of the optical coupler, and the second waveguide element (43) is configured to extend from the second end of the optical coupler towards the first end of the optical coupler, such that the first waveguide element (45) partly overlaps with the second waveguide element (43) to adapt light passing between the first end (45a) of the first waveguide element (45) and first end (43a) of the second waveguide element (43).