Ge/Si Ring Resonator Modulators for Optical Data Communications
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Solution Overview
Problem
The development of high-speed, compact, and low-power optical modulators for silicon photonics is hindered by the high refractive index contrast between Si and Ge, leading to low coupling efficiency and Q-factor issues in Ge/Si ring resonators, which result in small coupling efficiency and low extinction ratios.
Innovation Solution
The use of Ge or SiGe ring resonators with doped poly-Si layers and short channel waveguides for enhanced lateral coupling, combined with full 3D FDTD simulations for optimal design, allowing for ultrafast modulation speeds and improved extinction ratios while maintaining compactness and low power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If Ge on Si is used for ring resonator modulator, then the footprint is reduced and integration is improved, but the coupling efficiency between Si waveguide and Ge ring becomes very small due to high refractive index contrast
Solution Approach 1:
The patent introduces SiGe as an intermediate material layer between Si waveguide and Ge ring resonator. This gradient index structure (Si-SiGe-Ge) serves as a mediator that gradually transitions the refractive index, enabling efficient coupling between the Si waveguide and Ge ring while maintaining the compact footprint of the Ge-based resonator.
2Area of stationary object
If Ge (or SiGe) ring is used with high Ge composition, then the refractive index contrast is increased for compact design, but the Q-factor becomes low due to intrinsic absorption resulting in low extinction ratio
Solution Approach 1:
The patent optimizes the Ge composition parameter in the ring resonator, using approximately 50% Ge content rather than pure Ge. This parameter change reduces intrinsic absorption losses while maintaining sufficient refractive index contrast for compact resonator design, thereby achieving both small footprint and high extinction ratio through balanced material composition.
3Area of stationary object
If ring resonator size is reduced for compact integration, then the footprint is minimized, but the coupling efficiency and Q-factor are degraded
Solution Approach 1:
The patent employs a composite material structure consisting of Si waveguide, SiGe intermediate layer, and Ge ring resonator. This composite design allows the small-radius Ge ring to achieve high Q-factor and efficient coupling by combining the advantages of different materials: Si provides low-loss waveguiding, SiGe provides gradient index coupling, and Ge provides high index contrast for compact resonance.
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 solution enables ring resonator modulators with high extinction ratios and low insertion loss, achieving ultrafast modulation speeds and compatibility with Si-CMOS platforms, reducing power consumption and enabling high-density integration.
Implementation Method 1
Epitaxial SiGe on Si has been proposed for modulator devices by using Franz-Keldysh effects
Data Source
AI summary
An optical modulator structure includes at least two waveguide structures for inputting and outputting an optical signal. At least one ring resonator structure provides coupling between the at least two waveguide structures. The at least one ring resonator structure includes Ge or SiGe.