Ultralow-Loss Interlayer Coupling for Silicon Photonics

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

Silicon photonics platforms face challenges in thermal isolation and increased loss due to abrupt transitions between silicon and silicon nitride waveguides, leading to mode mismatch, back reflection, and crosstalk, especially at high optical powers, which can damage components.

Innovation Solution

An interlayer transition coupling structure with a displacing waveguide section that gradually transitions between silicon and silicon nitride waveguides, avoiding abrupt ends and using evanescent-wave coupling to reduce mode mismatch, back reflection, and crosstalk.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Device complexity

If an abrupt transition is used between silicon and silicon nitride waveguides, then the device complexity is reduced, but mode mismatch, back reflection, and crosstalk increase

Engineering Contradiction:

Improvetransition structure complexityVSAvoidoptical coupling reliability

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

The transition structure is divided into multiple sections: a silicon waveguide section, a silicon nitride waveguide section, and an intermediate coupling section with gradually varying dimensions. This segmentation allows the optical mode to transition gradually through intermediate states, reducing mode mismatch and back reflection while maintaining manageable device complexity in each segment.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The transition is achieved by gradually varying the waveguide dimensions in the vertical dimension (height and width) along the propagation direction. The intermediate section features continuously changing cross-sectional dimensions that enable adiabatic mode transformation between silicon and silicon nitride waveguides, reducing optical losses without significantly increasing lateral footprint.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

2Loss of energy

If the Si substrate is placed far from the Si waveguide to avoid loss, then optical loss is reduced, but thermal isolation increases due to SiO2 being a poor thermal conductor

Engineering Contradiction:

Improveoptical lossVSAvoidthermal isolation

Core Design Contradiction:

Loss of energyVSTemperature

Solution Approach 1:

The design implements different spacing arrangements in different regions: in the interlayer transition coupling structure, the waveguides are positioned closer together to enable effective optical coupling, while in regions with active devices, sufficient spacing is maintained to provide thermal isolation. This local optimization allows the system to achieve both low optical loss and adequate thermal management where needed.

Inventive Principle:

Principle #3Local quality

3Adaptability or versatility

If silicon waveguides are used in functional devices, then active devices can be integrated on the same platform, but the waveguides suffer from linear and nonlinear absorption losses at high optical powers

Engineering Contradiction:

Improveplatform integration capabilityVSAvoidabsorption loss

Core Design Contradiction:

Adaptability or versatilityVSLoss of energy

Solution Approach 1:

The invention introduces silicon nitride waveguides as an intermediary material for the interlayer transition coupling structure. Silicon nitride exhibits low linear and nonlinear absorption, making it suitable for handling high optical powers. The coupling structure uses evanescent field interaction between silicon and silicon nitride waveguides to transfer optical signals, allowing silicon-based active devices to be integrated while the transition sections operate with lower-loss silicon nitride waveguides.

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 design achieves ultralow loss, low crosstalk, and reduced back reflection, improving the performance and reliability of optical couplers in silicon photonics platforms.

Implementation Method 1

using evanescent-wave coupling to reduce mode mismatch, back reflection, and crosstalk

Methodology Applied

Scientific EffectEvanescent-wave coupling:

Data Source

PatentUS20250306282A1Ultralow loss interlayer transition design for integrated multilayer photonic platform

Publication Date: 2025.10.02 WELLS FARGO BANK NA

AI summary

An interlayer transition coupling structure includes a first waveguide layer arranged in a cladding layer and configured to guide a first optical signal lengthwise along at least a first portion of the interlayer transition coupling structure; and a second waveguide layer arranged in the cladding layer and configured to guide a second optical signal lengthwise along at least a second portion of the interlayer transition coupling structure. The first waveguide layer and the second waveguide layer are spatially overlapped in a vertical direction in a third portion of the interlayer transition coupling structure. The first waveguide layer includes a displacing waveguide section that deviates from a tip section of the displacing waveguide section to avoid an abrupt layer-to-layer transition between the first waveguide layer and the second waveguide layer. An area of overlap between the displacing waveguide section and the second waveguide layer gradually changes.