Quasi-Phase Matched Semiconductor Waveguides for Efficient Second Harmonic Generation
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Solution Overview
Problem
Existing semiconductor waveguides with strain gradient effects for second-order harmonic generation have limitations such as poor efficiency, limited wavelength range, and material absorption issues, making them unsuitable for commercial applications, and the use of quasi-phase matching techniques is difficult to manufacture and applies high stresses that can lead to defects.
Innovation Solution
The solution involves creating semiconductor waveguides with periodically alternating sections of high and low optical mode coupling coefficients, where high X2 sections are strained and low X2 sections are not, using materials like silicon and germanium, and inducing strain through stress films or lattice mismatches, eliminating the need to reverse the sign of the X2 effect and achieving phase matching without applying both tensile and compressive stress.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If strain gradient is applied to achieve second order harmonic generation in silicon waveguide, then SHG effects are obtained, but conversion efficiency is poor due to lack of phase matching
Solution Approach 1:
The patent applies periodic poling of the silicon waveguide, creating alternating regions of compressive and tensile strain with a period equal to the coherence length. This periodic modulation of the strain field enables quasi-phase matching, allowing efficient energy transfer from pump to signal and idler waves throughout the waveguide length, thereby resolving the efficiency problem while maintaining SHG effects
2Productivity
If alternating compressive and tensile strain directions are applied to provide phase matching, then second order effects are achieved, but high stresses lead to defects or crystal structure failure
Solution Approach 1:
The patent applies strain locally through targeted stressor placement rather than uniform alternating strain. Stressors are positioned to induce compressive strain in specific regions while adjacent regions experience tensile strain from the substrate lattice mismatch, achieving the required strain gradient for SHG without subjecting the entire crystal to high alternating stresses that would cause defects or failure
3Reliability
If strain is applied to achieve second order optical effects, then X2 coupling is enhanced, but wavelength range is limited due to material absorption
Solution Approach 1:
The patent changes the material composition parameter by using silicon-germanium alloys with varying germanium concentrations in different waveguide regions. This allows tuning of the optical properties and absorption characteristics across different wavelength ranges while maintaining the strain-induced second order effects, thereby extending the operational wavelength range beyond what pure silicon can achieve
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 enables efficient second-order optical effects across a desired wavelength range, overcoming the limitations of existing waveguides by reducing strain in sections without high X2 effects and using materials like silicon and germanium, enhancing phase matching and reducing the risk of material defects.
Implementation Method 1
inducing strain in the first sections by: (i) applying a high-stress material to at least the first sections, or (ii) inducing strain in the first sections by forming the waveguide body on a substrate having a lattice and/or thermal mismatch with the waveguide body
Data Source
AI summary
Quasi-phase matched (QPM), semiconductor photonic waveguides include periodically-poled alternating first and second sections. The first sections exhibit a high degree of optical coupling (abbreviated “X2”), while the second sections have a low X2. The alternating first and second sections may comprise high-strain and low-strain sections made of different material states (such as crystalline and amorphous material states) that exhibit high and low X2 properties when formed on a particular substrate, and/or strained corrugated sections of different widths. The QPM semiconductor waveguides may be implemented as silicon-on-insulator (SOI), or germanium-on-silicon structures compatible with standard CMOS processes, or as silicon-on-sapphire (SOS) structures.