Fiber-to-chip coupler with tapered waveguide and high-index cap

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Solution Overview

Problem

The efficient coupling of light from a standard optical fiber to on-chip photonic waveguides is challenging due to the size mismatch between the fundamental mode of the optical fiber and the waveguide, leading to significant coupling losses that can eliminate quantum advantages in digital computing and communications.

Innovation Solution

The development of fiber-to-chip couplers with tapered regions and caps made of higher refractive index materials, which adiabatically increase in width to efficiently transfer light from the optical fiber to the waveguide, preventing leakage into substrate modes and enhancing coupling efficiency.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Device complexity

If direct coupling between optical fiber and waveguide is used, then device complexity is reduced, but coupling efficiency deteriorates due to size mismatch

Engineering Contradiction:

Improvecoupler structureVSAvoidcoupling loss

Core Design Contradiction:

Device complexityVSLoss of energy

Solution Approach 1:

The patent introduces a tapered waveguide section as an intermediary structure between the optical fiber and the submicron waveguide. This tapered section acts as a mediator that gradually transforms the mode field diameter from the fiber scale to the waveguide scale, enabling efficient power transfer while maintaining relatively simple device architecture.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent employs parameter changes by varying the width of the waveguide in the tapered section. The waveguide width transitions from a larger dimension at the fiber interface to a smaller dimension at the submicron waveguide interface, creating a gradual impedance transformation that minimizes reflection and maximizes coupling efficiency.

Inventive Principle:

Principle #35Parameter changes

2Loss of energy

If tapered waveguide region is introduced to improve coupling, then coupling efficiency is improved, but device complexity increases

Engineering Contradiction:

Improvecoupling lossVSAvoidcoupler structure

Core Design Contradiction:

Loss of energyVSDevice complexity

Solution Approach 1:

The coupler structure is segmented into distinct functional regions: a tapered waveguide section for mode transformation, a higher-index cap region for field confinement, and the submicron waveguide section for on-chip integration. This segmentation allows each region to be optimized for its specific function while maintaining overall structural simplicity.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent uses composite material structures by combining different refractive index materials - the base waveguide material, the higher-index cap material, and the fiber material. This composite approach enables precise control of the optical field distribution and enhances coupling efficiency through refractive index engineering.

Inventive Principle:

Principle #40Composite materials

3Loss of energy

If higher-index cap is added to prevent leakage, then coupling efficiency is improved, but manufacturing complexity increases

Engineering Contradiction:

Improvepower leakageVSAvoidfabrication process

Core Design Contradiction:

Loss of energyVSEase of manufacture

Solution Approach 1:

The higher-index cap is applied locally only to the tapered waveguide region where it is most needed for field confinement, rather than covering the entire waveguide structure. This local application minimizes the impact on manufacturing processes while providing the necessary optical confinement to prevent power leakage into the substrate.

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 solution significantly reduces coupling losses, ensuring efficient light transfer and maintaining quantum advantages in digital computing and communications by effectively bridging the size gap between optical fibers and waveguides.

Implementation Method 1

a tapered-waveguide region. The tapered-waveguide region has a width that, in an axial direction perpendicular to the transverse direction, adiabatically increases from a minimum width to the uniform width

Methodology Applied

Scientific EffectAdiabatic transformation:

Implementation Method 2

The cap extends from the tapered fiber tip toward the cylindrical section, is formed of a second material having a cap refractive index that exceeds the fiber refractive index, and includes a cap-region disposed on the tapered-waveguide region

Methodology Applied

Scientific EffectTotal internal reflection: Total Internal Reflection

Data Source

PatentUS11480736B2Fiber-to-chip coupler

Publication Date: 2022.10.25 THE REGENTS OF THE UNIVERSITY OF COLORADO

AI summary

A fiber-to-chip coupler includes a substrate, a waveguide on a top surface of the substrate, an optical fiber axially aligned to the waveguide, and a cap. The waveguide has a uniform region with uniform width and a tapered-waveguide region having a width that adiabatically increases from a minimum width to the uniform width. The optical fiber has a tapered fiber tip having a minimum core diameter, a cylindrical section having a maximum core diameter, and a tapered-fiber section therebetween. The optical fiber is located at least in part above the tapered-waveguide region, and has a core diameter that adiabatically decreases within a taper length of the tapered-fiber section. The cap extends from the tapered fiber tip toward the cylindrical section, is formed of a second material having a cap refractive index that exceeds a refractive index of the optical fiber, and includes a cap-region disposed on the tapered-waveguide region.