Narrow Third Waveguide for Adiabatic Transition in SiN-on-Si Optical Devices

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Solution Overview

Problem

Conventional optical devices experience increased optical loss due to light radiation to the substrate, which affects the efficiency of adiabatic conversion and coupling with optical fibers, particularly because the refractive index of the Si substrate is higher than that of SiN waveguides, leading to increased coupling loss.

Innovation Solution

The optical device incorporates a third waveguide with a narrower width than the first and second waveguides, positioned between them to facilitate adiabatic transition and reduce light radiation to the substrate, thereby improving coupling efficiency and reducing the size of the device.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Loss of energy

If a conventional waveguide structure is used with SiN waveguides on Si substrate, then the device structure is simple, but optical loss increases due to light radiation to the substrate

Engineering Contradiction:

Improveoptical lossVSAvoidwaveguide structure complexity

Core Design Contradiction:

Loss of energyVSDevice complexity

Solution Approach 1:

The patent introduces a third waveguide made of SiN material with a narrower width than the first and second waveguides, positioned between them to facilitate adiabatic transition. This intermediate waveguide acts as a mediator that enables efficient optical transition while suppressing light radiation to the high-refractive-index Si substrate, thereby reducing optical loss without requiring fundamentally new structural concepts

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent applies different waveguide widths at different positions within the adiabatic conversion section. The third waveguide has a narrower width than the first and second waveguides, creating localized structural variations that optimize the adiabatic transition process and reduce light radiation to the substrate while maintaining overall structural simplicity

Inventive Principle:

Principle #3Local quality

2Reliability

If the waveguide width is increased to reduce coupling loss with optical fibers, then coupling efficiency improves, but the device size increases

Engineering Contradiction:

Improvecoupling efficiencyVSAvoiddevice size

Core Design Contradiction:

ReliabilityVSVolume of moving object

Solution Approach 1:

The patent optimizes the waveguide width parameter by introducing a third waveguide with a narrower width than the first and second waveguides. This parameter change enables efficient adiabatic transition and reduces light radiation to the substrate, improving coupling efficiency while maintaining a compact device size. The specific width ratio and dimensional parameters are carefully selected to achieve optimal performance

Inventive Principle:

Principle #35Parameter changes

3Reliability

If the adiabatic conversion section is made longer to improve conversion efficiency, then the conversion efficiency improves, but the device size increases

Engineering Contradiction:

Improveadiabatic conversion efficiencyVSAvoidconversion section length

Core Design Contradiction:

ReliabilityVSLength of stationary object

Solution Approach 1:

The patent creates localized structural variations within the adiabatic conversion section by introducing a third waveguide with a narrower width positioned between the first and second waveguides. This local structural optimization enhances the adiabatic transition efficiency without requiring an increase in the overall length of the conversion section, thereby improving conversion efficiency while maintaining a compact device footprint

Inventive Principle:

Principle #3Local quality

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 enhances the adiabatic conversion efficiency without increasing the size of the adiabatic conversion section, reduces optical loss, and minimizes the device's size by suppressing light radiation to the substrate, thereby improving coupling efficiency with optical fibers.

Implementation Method 1

light is adiabatically and optically transitioned between the first waveguide 102 and the second waveguide 104

Methodology Applied

Scientific EffectAdiabatic transition:

Implementation Method 2

a first waveguide 102 that is covered by the clad 111 and that is made of, for example, Si3N4

Methodology Applied

Scientific EffectTotal internal reflection: Total Internal Reflection

Data Source

PatentUS20240310577A1Optical device, optical transmitter, and optical receiver

Publication Date: 2024.09.19 FUJITSU OPTICAL COMPONENTS LTD

AI summary

An optical device includes a substrate, a first layer provided on the substrate on a side away from the substrate, a second layer provided on the substrate on a side closer to the substrate, and a third layer provided between the first layer and the second layer. The optical device includes a first waveguide arranged in the first layer, a second waveguide arranged in the second layer, a third waveguide arranged in the third layer, and a fourth waveguide arranged between the second layer and the substrate. The third waveguide is arranged at a position in which at least the first waveguide and a part of the second waveguide are overlapped in a surface direction of the substrate, and has a structure in which a width of the third waveguide is set to be narrower than a width of each of the first waveguide and the second waveguide.