1D Apodized Grating Coupler Structure for Back-Reflection Suppression

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Solution Overview

Problem

Current grating couplers in silicon photonics suffer from high back-reflection, which leads to optical noise and instability in optical circuits, particularly in visible light applications, and existing methods do not provide high coupling efficiency and low back reflection characteristics.

Innovation Solution

Implementing a 1D apodized grating coupler with two distinct etching levels, including a medium and shallow etched grating regions, to optimize geometric variations and reduce back-reflection, thereby enhancing coupling efficiency and stability.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If conventional grating couplers are used to achieve compact integration, then coupling efficiency is improved, but back-reflection increases causing optical noise and instability

Engineering Contradiction:

Improveoptical stabilityVSAvoidback-reflection

Core Design Contradiction:

ReliabilityVSObject-generated harmful factors

Solution Approach 1:

The grating coupler is divided into multiple regions with different etching depths (first region with first depth, second region with second depth). This segmentation allows different portions of the grating to contribute differently to coupling and back-reflection, enabling independent optimization of coupling efficiency and back-reflection suppression.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different regions of the grating coupler are given different local properties through varying etching depths. The first region has a first etching depth optimized for coupling, while the second region has a second etching depth optimized for reducing back-reflection. This local quality variation allows the structure to simultaneously achieve high coupling efficiency and low back-reflection.

Inventive Principle:

Principle #3Local quality

2Productivity

If high-efficiency grating couplers are implemented, then coupling efficiency is improved, but back-reflection losses increase to around -17 dB or worse

Engineering Contradiction:

Improvecoupling efficiencyVSAvoidback-reflection losses

Core Design Contradiction:

ProductivityVSLoss of energy

Solution Approach 1:

The grating coupler structure is segmented into at least two regions with different etching depths. The first region (with first etching depth) and second region (with second etching depth) work together to achieve both high coupling efficiency and reduced back-reflection losses, overcoming the trade-off between these two parameters.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The etching depth parameter is varied across different regions of the grating coupler. By changing the etching depth from the first depth in the first region to the second depth in the second region, the optical properties are optimized to simultaneously achieve high coupling efficiency and minimize back-reflection losses.

Inventive Principle:

Principle #35Parameter changes

3Ease of manufacture

If single-level etched gratings are used for simple fabrication, then manufacturing complexity is reduced, but back-reflection and optical noise increase

Engineering Contradiction:

Improvefabrication simplicityVSAvoidoptical noise

Core Design Contradiction:

Ease of manufactureVSObject-generated harmful factors

Solution Approach 1:

The grating coupler is segmented into multiple etching regions with different depths. This segmentation reduces back-reflection and optical noise while maintaining compatibility with standard semiconductor fabrication processes, thus balancing manufacturing ease with optical performance.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The grating coupler employs a composite structure with regions of different etching depths, creating an effective composite optical structure that reduces back-reflection and optical noise while remaining manufacturable using conventional fabrication techniques.

Inventive Principle:

Principle #40Composite materials

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 solution achieves reduced back-reflection losses and improved coupling efficiency, leading to lower optical noise and increased stability in optical communication systems.

Implementation Method 1

a first grating region comprising a first plurality of gratings... a second grating region comprising a second plurality of gratings

Methodology Applied

Scientific EffectDiffraction: Diffraction

Implementation Method 2

forming a cladding layer on the first and second grating regions, wherein the cladding layer has a different refractive index from the substrate layer

Methodology Applied

Scientific EffectRefraction: Refraction

Data Source

PatentUS20250355190A11d apodized grating devices and methods for suppressing optical noise

Publication Date: 2025.11.20 TAIWAN SEMICONDUCTOR MANUFACTURING CO LTD

AI summary

A method of making a grating coupler includes etching a first grating region into a substrate layer, wherein the first grating region comprises a first plurality of gratings having a first height and a first pitch between adjacent gratings of the first plurality of gratings. The method further includes etching a second grating region into the substrate layer, wherein the second grating region comprises a second plurality of gratings having a second height, different from the first height, and a second pitch between adjacent grating of the second plurality of gratings. The method further includes forming a cladding layer on the first and second grating regions, wherein the cladding layer has a different refractive index from the substrate layer.