3D Taper Structures for Low-Loss Optical Coupling
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Solution Overview
Problem
Integrating efficient light modulators with silicon-based optical waveguides is challenging due to the need for epitaxial growth of active material layers, which results in high optical-coupling loss when coupling light to and from sub-micron silicon optical waveguides.
Innovation Solution
The use of 3-dimensional taper structures on optical waveguides to match the spatial extent of optical modes between the waveguides and optical modulators, reducing optical-coupling loss by adjusting cross-sectional areas and heights of the tapers to approximate those of the modulators, thereby facilitating low-loss light coupling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If epitaxial growth is used to fabricate electro-absorption light modulators with sub-micron on-chip silicon optical waveguides, then the active material layers can be integrated with silicon waveguides, but high optical-coupling loss occurs when coupling light to and from the waveguides
Solution Approach 1:
The patent introduces silicon-germanium (SiGe) layer structures as intermediary components between the silicon optical waveguide and the electro-absorption light modulator. These SiGe layers serve as transition zones that facilitate efficient optical coupling by matching the mode profiles between the waveguide and modulator, thereby reducing optical-coupling loss while enabling integration of epitaxially-grown active material layers with silicon waveguides
2Volume of moving object
If sub-micron silicon optical waveguides are used to carry optical signals, then the device size can be reduced, but it becomes difficult to couple light to and from the active material layers with low optical loss
Solution Approach 1:
The patent employs three-dimensional SiGe layer structures that extend vertically from the planar silicon waveguide. These 3D structures create a gradual transition in the optical mode profile by varying the layer thickness and composition in the vertical dimension, enabling efficient coupling between the sub-micron waveguide and the active material layers while maintaining compact device footprint
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 approach significantly reduces optical-coupling loss, enabling effective integration of optical modulators with on-chip silicon waveguides and improving the efficiency of light modulation and detection processes.
Implementation Method 1
a cross-sectional area of a given 3-D taper structure, which can be one of the first 3-D taper structure and the second 3-D taper structure, increases from a second value distal to the given end to the first value proximate to the given end, thereby reducing optical-coupling loss by approximately matching a spatial extent of an optical mode in the optical waveguide and a spatial extent of an optical mode in the optical modulator
Data Source
AI summary
An integrated circuit that includes an optical waveguide defined in a semiconductor layer is described. In this integrated circuit, light is coupled between the optical waveguide and an optical modulator, which is disposed on the optical waveguide, using 3-dimensional (3-D) taper structures that are proximate to the ends of the optical modulator. The cross-sectional areas of these 3-D taper structures transition, over a distance, from that of the optical waveguide (distal from the optical modulator) to that of optical modulator (proximate to the ends of the optical modulator). In this way, a spatial extent of an optical mode in the optical waveguide and a spatial extent of the optical mode in the optical modulator may be approximately matched to reduce the optical loss when the light is coupled to or from the optical modulator.