Optical Waveguide Isolation Structure for Low-Crosstalk Dense Layouts

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Solution Overview

Problem

The challenge in silicon photonics is the high crosstalk and power coupling between adjacent optical waveguides due to insufficient spacing, leading to increased layout area and inefficiencies in photonic integrated circuits.

Innovation Solution

Incorporating air seams or voids as optical isolation structures between adjacent waveguides, reducing the spacing distance while maintaining compatibility with CMOS manufacturing processes.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Object-generated harmful factors

If air seams or voids are incorporated as optical isolation structures between adjacent waveguides, then crosstalk and power coupling between waveguides are reduced, but the manufacturing process complexity increases

Engineering Contradiction:

Improvecrosstalk and power coupling between waveguidesVSAvoidmanufacturing process complexity

Core Design Contradiction:

Object-generated harmful factorsVSDevice complexity

Solution Approach 1:

Air seams or voids are introduced as intermediary structures between adjacent waveguides to reduce optical coupling and crosstalk. These air gaps act as optical isolators that prevent harmful electromagnetic field interactions while maintaining physical separation between waveguide structures.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent utilizes air-filled voids or porous structures between waveguides to create optical isolation. The air gaps function as low-refractive-index materials that reduce evanescent field coupling between adjacent waveguides, thereby minimizing crosstalk and power transfer.

Inventive Principle:

Principle #31Porous materials

2Area of stationary object

If spacing distance between adjacent waveguides is reduced to decrease layout area, then integration density increases, but crosstalk and power coupling between waveguides increase

Engineering Contradiction:

Improvelayout area of photonic circuitVSAvoidcrosstalk and power coupling between waveguides

Core Design Contradiction:

Area of stationary objectVSObject-generated harmful factors

Solution Approach 1:

Air seams serve as intermediary isolation structures that enable tight waveguide spacing while preventing optical coupling. The air gaps act as optical barriers that allow waveguides to be placed closer together without increasing crosstalk, thus reducing overall layout area while maintaining signal isolation.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent changes the refractive index parameter by introducing air gaps (refractive index ≈1.0) between waveguides. This parameter change creates a high-contrast optical isolation that allows reduced spacing distances while maintaining low crosstalk levels, enabling higher integration density.

Inventive Principle:

Principle #35Parameter changes

3Manufacturing precision

If air seams are sealed within dielectric portions using multiple deposition/sputtering operations, then manufacturing precision is improved, but the number of manufacturing steps increases

Engineering Contradiction:

Improveprecision of air seam formation and sealingVSAvoidmanufacturing throughput

Core Design Contradiction:

Manufacturing precisionVSProductivity

Solution Approach 1:

Trenches are formed in the semiconductor layer before waveguide fabrication to define the air seam locations. This preliminary structuring enables precise air gap formation and sealing during subsequent dielectric deposition steps, ensuring manufacturing precision while organizing the process sequence efficiently.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The air seam formation process is segmented into multiple controlled deposition/sputtering operations, with each step creating or sealing a specific portion of the air gap structure. This segmentation allows precise control over air seam dimensions and positioning, achieving high manufacturing precision through staged process control.

Inventive Principle:

Principle #1Segmentation

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 reduces the layout area by at least 50% and enhances the integration density of photonic components, supporting multiple functionalities on a single chip with reduced crosstalk and power coupling.

Implementation Method 1

Incorporating air seams or voids as optical isolation structures between adjacent waveguides, reducing the spacing distance while maintaining compatibility with CMOS manufacturing processes

Methodology Applied

Scientific EffectOptical isolation: Refraction

Data Source

PatentUS20260086286A1Method for forming optical waveguide structure

Publication Date: 2026.03.26 TAIWAN SEMICONDUCTOR MANUFACTURING CO LTD

AI summary

A semiconductor photonic device includes a semiconductor waveguide, a cladding structure surrounding the semiconductor waveguide, and an optical isolation structure disposed in the cladding structure. A top surface of the optical isolation structure is lower than a top surface of the semiconductor waveguide, and a bottom surface of the optical isolation structure is higher than a bottom surface of the semiconductor waveguide.