Graphene Silicon Optical Modulator Mid-Infrared Integration

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Solution Overview

Problem

Existing silicon-based optical modulators are not suitable for the mid-infrared region due to increased electro-absorption effects, and graphene-based modulators in this region rely on free-space coupling, which is not compatible with silicon platforms, limiting their integration and performance.

Innovation Solution

A graphene-based optical modulator is developed using a surface plasmon waveguide configuration on a silicon platform, with a dielectric-loaded waveguide designed to maximize light intensity overlap with the graphene layer, enabling efficient modulation in the mid-infrared region by tuning the graphene's transmission state with electrical signals.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If silicon-based optical modulators are used in the mid-infrared region, then integration with silicon platform is achieved, but electro-absorption effects increase and modulation performance deteriorates

Engineering Contradiction:

Improveintegration compatibilityVSAvoidmodulation performance

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The patent employs a hybrid structure combining silicon waveguide with graphene layer. The silicon platform provides integration compatibility and waveguiding functionality, while the graphene layer enables effective modulation in the mid-infrared region by controlling carrier concentration through electrical gating, thereby overcoming the electro-absorption limitations of pure silicon modulators at these wavelengths.

Inventive Principle:

Principle #40Composite materials

Solution Approach 2:

The patent applies different material properties to different regions: the silicon waveguide core provides optical confinement and platform integration, while the graphene layer deposited on the waveguide surface provides the modulation function. This local differentiation allows each material to optimize its contribution - silicon for integration and graphene for mid-infrared modulation performance.

Inventive Principle:

Principle #3Local quality

2Reliability

If graphene-based modulators with free-space coupling are used in the mid-infrared region, then modulation performance is improved, but compatibility with silicon platform is lost

Engineering Contradiction:

Improvemodulation performanceVSAvoidplatform compatibility

Core Design Contradiction:

ReliabilityVSAdaptability or versatility

Solution Approach 1:

The silicon waveguide acts as an intermediary between the free-space optical field and the graphene layer. It couples the mid-infrared light into the graphene-modulated region through evanescent field interaction, enabling graphene's superior modulation performance while maintaining compatibility with the silicon photonic platform through standardized waveguide interfaces.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Productivity

If waveguide configuration is optimized to maximize light intensity overlap with graphene layer, then modulation efficiency is improved, but device complexity increases

Engineering Contradiction:

Improvemodulation efficiencyVSAvoidwaveguide design complexity

Core Design Contradiction:

ProductivityVSDevice complexity

Solution Approach 1:

The patent employs dynamically controllable carrier concentration in the graphene layer through electrical gating. By adjusting the gate voltage, the Fermi level and carrier density can be tuned to optimize the interaction between light and graphene, thereby maximizing modulation efficiency without requiring complex static waveguide geometries. This dynamic control simplifies the overall device design while achieving high performance.

Inventive Principle:

Principle #15Dynamics

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 configuration achieves broadband optical modulation with high efficiency and compatibility with other silicon platform components, supporting operation up to 5 GHz and extending the modulator's functionality across a wide optical bandwidth.

Implementation Method 1

A graphene-based optical modulator is developed using a surface plasmon waveguide configuration on a silicon platform

Methodology Applied

Scientific EffectSurface plasmon:

Implementation Method 2

the increased interaction length through evanescent coupling helps realize a sufficient modulation depth

Methodology Applied

Scientific EffectEvanescent coupling:

Implementation Method 3

The electrostatic doping of graphene would block the interband optical transitions with energy less than two times the Fermi energy of graphene due to the Pauli-blocking principle

Methodology Applied

Scientific EffectPauli-blocking principle:

Implementation Method 4

The electrostatic doping of graphene would block the interband optical transitions

Methodology Applied

Scientific EffectElectrostatic doping:

Data Source

PatentUS11372271B2Optical modulator, method for forming the same, and method for controlling the same

Publication Date: 2022.06.28 NANYANG TECH UNIV

AI summary

According to embodiments of the present invention, an optical modulator is provided. The optical modulator includes a substrate, and a waveguiding arrangement on the substrate, the waveguiding arrangement having a waveguide, and at least one graphene layer arranged to interact with light propagating in the waveguiding arrangement, wherein the waveguide is designed such that the light interacting with the at least one graphene layer has a maximum intensity overlapping with the at least one graphene layer. According to further embodiments of the present invention, a method for forming the optical modulator, and a method for controlling the optical modulator are also provided.