Airgap Waveguide Core Structure for Edge Coupler Mode Confinement

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Solution Overview

Problem

Edge couplers in photonics chips struggle to fully confine the electromagnetic field of incident light modes due to the inverse taper's narrow tip, leading to significant mode leakage and inefficient mode transformation.

Innovation Solution

Incorporating an airgap that surrounds the waveguide core, formed by removing sacrificial organic materials to create cavities filled with air or low-index gas, which acts as low-index cladding to enhance mode confinement and improve mode transformation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If the inverse taper tip cross-sectional area is reduced to improve mode transformation, then mode transformation capability is improved, but electromagnetic field confinement deteriorates

Engineering Contradiction:

Improvemode transformation capabilityVSAvoidelectromagnetic field confinement

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The patent introduces an airgap as an intermediary structure between the waveguide core and the surrounding dielectric layer. This airgap acts as a low-index cladding that mediates the interaction between the incident light mode and the waveguide core, enabling effective mode transformation while maintaining electromagnetic field confinement through the inverse taper mechanism.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Adaptability or versatility

If the inverse taper tip cross-sectional area is reduced to improve mode transformation, then mode transformation capability is improved, but mode leakage increases

Engineering Contradiction:

Improvemode transformation capabilityVSAvoidmode leakage

Core Design Contradiction:

Adaptability or versatilityVSLoss of energy

Solution Approach 1:

The airgap serves as an intermediary low-index structure that prevents mode leakage by providing a refractive index gradient between the waveguide core and the external dielectric layer. This gradient guides the electromagnetic field back into the waveguide core during mode transformation, reducing energy loss.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent changes the refractive index parameter by introducing an airgap (n≈1.0) surrounding the waveguide core (n>1.0), creating a refractive index gradient that controls mode transformation and prevents leakage. This parameter change enables the inverse taper to effectively confine modes while maintaining transformation capability.

Inventive Principle:

Principle #35Parameter changes

3Strength

If conventional dielectric cladding is used around the waveguide core, then structural support is provided, but mode confinement effectiveness is reduced

Engineering Contradiction:

Improvestructural supportVSAvoidmode confinement effectiveness

Core Design Contradiction:

StrengthVSReliability

Solution Approach 1:

The airgap acts as an intermediary low-index cladding layer that replaces conventional high-index dielectric cladding. This intermediary structure provides the necessary refractive index contrast for effective mode confinement while maintaining structural support through the waveguide core geometry and surrounding dielectric layer.

Inventive Principle:

Principle #24Intermediary (Mediator)

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 airgap structure effectively confines the electromagnetic field, enhancing mode transformation and reducing leakage, thereby improving the efficiency of light coupling in photonics chips.

Implementation Method 1

the airgap... acts as low-index cladding to enhance mode confinement

Methodology Applied

Scientific EffectRefraction: Refraction

Data Source

PatentUS12529846B2Waveguide cores surrounded by an airgap

Publication Date: 2026.01.20 GLOBALFOUNDRIES US INC

AI summary

Structures for an edge coupler and methods of forming a structure for an edge coupler. The structure comprises a substrate, a dielectric layer over the substrate, and a waveguide core over the substrate. The structure further comprises an airgap that extends at least partially through the dielectric layer and that surrounds a plurality of sides of a portion of the waveguide core.