Back-End-of-Line Edge Coupler Tapered Grating Light Leakage

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Solution Overview

Problem

Conventional edge couplers in photonics chips experience significant light leakage loss due to a mismatch between the large mode size of the light source and the small dimensions of the coupler, particularly when receiving light from a single-mode optical fiber, leading to inefficiencies in mode transformation and increased operational overhead.

Innovation Solution

A back-end-of-line edge coupler structure featuring a waveguide core and a multiple-taper grating positioned vertically between the substrate and the waveguide core, with segments arranged in a spaced-apart manner to align parallel to the waveguide core's longitudinal axis, reducing light leakage by enhancing mode conversion and minimizing insertion loss.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Area of stationary object

If a conventional edge coupler is used with small dimensions to integrate on the photonics chip, then the layout area and integration are improved, but the light confinement capability deteriorates causing significant leakage loss to the substrate

Engineering Contradiction:

Improvelayout areaVSAvoidlight leakage loss

Core Design Contradiction:

Area of stationary objectVSLoss of energy

Solution Approach 1:

The patent introduces a grating structure as an intermediary element positioned between the optical fiber and the waveguide core. This grating acts as a mediator that facilitates mode transformation and improves light confinement, enabling efficient coupling while maintaining the compact dimensions of the edge coupler on the photonics chip.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent modifies the physical parameters of the edge coupler by implementing a tapered waveguide core with varying dimensions along its length. The width and height of the waveguide core are gradually changed from the input end to the output end, transforming the mode size to match the optical fiber mode and improve light confinement, thereby reducing leakage loss while maintaining compact integration.

Inventive Principle:

Principle #35Parameter changes

2Loss of energy

If the edge coupler dimensions are increased to improve light confinement and reduce leakage loss, then the light confinement capability is improved, but the layout area increases reducing integration efficiency

Engineering Contradiction:

Improvelight leakage lossVSAvoidlayout area

Core Design Contradiction:

Loss of energyVSArea of stationary object

Solution Approach 1:

The patent divides the grating structure into multiple segments positioned at different locations along the edge coupler. This segmentation allows the grating to perform mode transformation functions in a compact configuration, achieving effective light confinement and reduced leakage loss without requiring a large overall layout area, thus maintaining integration efficiency.

Inventive Principle:

Principle #1Segmentation

3Adaptability or versatility

If a conventional edge coupler receives light from a single-mode optical fiber, then the compatibility with standard light sources is improved, but the mode mismatch increases causing higher leakage loss

Engineering Contradiction:

Improvecompatibility with light sourceVSAvoidleakage loss

Core Design Contradiction:

Adaptability or versatilityVSLoss of energy

Solution Approach 1:

The patent employs a tapered waveguide core structure where the dimensional parameters (width and height) are gradually transformed from the input end to the output end. This continuous parameter change enables smooth mode transformation that adapts the waveguide mode to match the single-mode optical fiber mode, reducing mode mismatch and minimizing leakage loss while maintaining compatibility with standard light sources.

Inventive Principle:

Principle #35Parameter changes

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 proposed structure significantly reduces light leakage to the substrate, allowing for improved mode conversion and through-band performance with reduced mode fluctuations, eliminating the need for an undercut and simplifying the fabrication process by maintaining a solid substrate beneath the edge coupler.

Implementation Method 1

a grating positioned in a vertical direction between the substrate and the waveguide core

Methodology Applied

Scientific EffectDiffraction: Diffraction

Implementation Method 2

the grating includes a second longitudinal axis and a plurality of segments positioned with a spaced-apart arrangement along the second longitudinal axis

Methodology Applied

Scientific EffectInterference: Interference

Implementation Method 3

a waveguide core including a first longitudinal axis... supporting mode transformation and mode size variation associated with mode conversion

Methodology Applied

Scientific EffectTotal internal reflection: Total Internal Reflection

Data Source

PatentUS12147075B2Back-end-of-line edge couplers with a tapered grating

Publication Date: 2024.11.19 GLOBALFOUNDRIES US INC

AI summary

Structures for an edge coupler and methods of fabricating such structures. The structure comprises a substrate and a back-end-of-line edge coupler including a waveguide core and a grating positioned in a vertical direction between the substrate and the waveguide core. The first waveguide core includes a first longitudinal axis, the grating includes a second longitudinal axis and a plurality of segments positioned with a spaced-apart arrangement along the second longitudinal axis, and the second longitudinal axis is aligned substantially parallel to the first longitudinal axis.