GeSi Optical Modulator Array Strain Engineering
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Solution Overview
Problem
Conventional silicon phase-shift modulators face limitations due to carrier recombination, high power consumption, and large device footprints, while group III-V electro-absorption modulators are CMOS-incompatible, making it challenging to integrate multiple modulators for broadband modulation in silicon-based systems.
Innovation Solution
An integrated optical modulator circuit with a stressor material applied to GeSi modulators, allowing multiple modulators to operate at different wavelengths by varying the strain, enabling a single modulator array to cover broad telecommunication bands with reduced fabrication costs and complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If multiple modulators are fabricated individually for different wavelengths, then broadband modulation coverage is achieved, but fabrication cost and system integration complexity increase dramatically
Solution Approach 1:
A single GeSi modulator array is designed to perform multiple wavelength modulation functions simultaneously. By incorporating multiple modulators with different active region widths in one array, the system achieves broadband coverage across O-band and C-band without requiring separate fabrication processes for each wavelength, thus reducing overall fabrication complexity while maintaining versatility
Solution Approach 2:
The modulator array is segmented into multiple individual modulators within the same structure, each with different active region widths (e.g., 200nm, 400nm, 600nm, 800nm, 1000nm). This segmentation allows each segment to operate at different wavelengths while being fabricated together as a unified structure, resolving the contradiction between achieving broadband coverage and maintaining simple fabrication
2Power
If GeSi modulator active region width is increased, then modulation wavelength shifts to longer wavelengths, but device footprint increases
Solution Approach 1:
Instead of adjusting wavelength by changing the length of the modulator structure, the invention uses the width dimension of the active region as the controlling parameter. By varying the active region width while keeping the modulator length constant, different wavelengths are achieved without increasing the overall device footprint, thus resolving the contradiction between wavelength tuning and compactness
3Adaptability or versatility
If stressor material is applied to shift modulation wavelength, then wavelength tuning is achieved, but fabrication process complexity increases
Solution Approach 1:
Different stressor materials (e.g., SiN, SiO2, GeSi) are applied locally to specific modulators within the array based on their target wavelength requirements. Each modulator receives stressor material with appropriate stress characteristics tailored to its specific width and wavelength goal, allowing precise wavelength tuning while maintaining overall process compatibility with standard CMOS fabrication
Solution Approach 2:
The invention uses stressor materials to change the physical parameter of strain in the GeSi layer, which directly shifts the modulation wavelength. By controlling the amount and type of stress applied through different stressor materials, wavelength tuning is achieved through physical parameter changes rather than requiring complex fabrication process modifications
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 allows for broadband modulation across multiple wavelengths with narrow spacing, suitable for wavelength division and multiplexing, achieving high data processing capacity with compact device layout and lower fabrication costs, while maintaining CMOS compatibility.
Implementation Method 1
a stressor material in contact with the optical modulator to apply a strain to the optical modulator
Implementation Method 2
A GeSi electro-absorption modulator employs the Franz-Keldysh effect, similar to group III-V direct band modulators. Applied electric field shifts the modulator material's direct band edge and increases its absorption coefficient.
Data Source
AI summary
An integrated optical modulator array useful for modulating light at different wavelengths in the same optical band includes multiple GeSi waveguides on a substrate. Each GeSi waveguide has a different width and is coupled to electrodes to form an electro-absorption modulator. A stressor material, such as SiN, disposed between the GeSi waveguides in the optical modulators applies a strain to the GeSi waveguides. Because each GeSi waveguide has a different width, it experiences a different strain. This difference can be a difference in magnitude, type (homogeneous v. inhomogeneous, compressive v. tensile), or both. The different strains shift the bandgaps of the Ge in the GeSi waveguides by different amounts, shifting the optical absorption edges for the GeSi waveguides by different amounts. Put differently, the stressor layer strains each GeSi modulator differently, causing each GeSi modulator to operate at a different wavelength.