2D Grating Coupler Layout for Low-PDL Optical Coupling

Solution Overview

Problem

Modern optical grating couplers face challenges in achieving high coupling efficiency and minimizing polarization-dependent loss (PDL) due to design constraints and mode mismatch, particularly in semiconductor devices.

Innovation Solution

A two-dimensional grating coupler with a taper section and grating section is designed using apodized grating patterns to enhance optical coupling performance, incorporating dual-mode gratings that adapt to the energy distribution of transverse electric (TE) and transverse magnetic (TM) modes, reducing PDL by optimizing duty cycles and pitches of gratings.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If conventional grating coupler designs are used, then manufacturing is simpler, but coupling efficiency is lower and polarization-dependent loss is higher

Engineering Contradiction:

Improvecoupling efficiencyVSAvoidgrating pattern complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The grating coupler is divided into multiple sections along the light propagation direction, with each section containing gratings of different orientations (e.g., 0-degree gratings in one section, 90-degree gratings in another section). This segmentation allows different polarization modes to be coupled efficiently at different locations, thereby improving overall coupling efficiency while managing the complexity through modular design

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different regions of the grating coupler are assigned different grating patterns and orientations tailored to local requirements. For example, regions optimized for TE mode coupling use specific grating configurations, while regions for TM mode coupling use different configurations. This local optimization improves coupling efficiency for each polarization mode without requiring the entire structure to be overly complex

Inventive Principle:

Principle #3Local quality

2Device complexity

If single-mode gratings are used, then device complexity is reduced, but polarization-dependent loss increases

Engineering Contradiction:

Improvegrating configuration simplicityVSAvoidpolarization-dependent loss

Core Design Contradiction:

Device complexityVSObject-affected harmful factors

Solution Approach 1:

The grating coupler is designed with multi-functional capabilities to handle both TE and TM polarization modes effectively. By incorporating gratings of different orientations and configurations within the same device, the system achieves universal coupling performance across polarization modes, reducing polarization-dependent loss while maintaining reasonable device complexity through integrated design

Inventive Principle:

Principle #6Universality (Multi-functionality)

3Reliability

If grating patterns are optimized for one polarization mode, then coupling efficiency for that mode improves, but coupling efficiency for the other mode deteriorates

Engineering Contradiction:

Improvecoupling efficiency for specific modeVSAvoidpolarization mode adaptability

Core Design Contradiction:

ReliabilityVSAdaptability or versatility

Solution Approach 1:

The grating coupler is divided into multiple sections along the light propagation direction, with each section containing gratings of different orientations (e.g., 0-degree gratings in one section, 90-degree gratings in another section). This segmentation allows different polarization modes to be coupled efficiently at different locations, thereby improving overall coupling efficiency while managing the complexity through modular design

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different regions of the grating coupler are assigned different grating patterns and orientations tailored to local requirements. For example, regions optimized for TE mode coupling use specific grating configurations, while regions for TM mode coupling use different configurations. This local optimization improves coupling efficiency for each polarization mode without requiring the entire structure to be overly complex

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

The proposed design significantly improves optical coupling efficiency while maintaining low PDL, effectively transferring light between optical fibers and waveguides in semiconductor devices.

Implementation Method 1

a grating section configured to be optically coupled to an optical fiber

Methodology Applied

Scientific EffectDiffraction: Diffraction

Data Source

PatentUS20250355188A1Two-dimensional grating coupler and method of forming the same

Publication Date: 2025.11.20 TAIWAN SEMICONDUCTOR MANUFACTURING CO LTD

AI summary

A method of forming a grating coupler includes: providing a design layout of the grating coupler, wherein the design layout includes: a taper section, comprising a pair of tapers; and a grating section coupled to the taper section, a grating section coupled to the taper section, the grating section including an array of gratings, wherein the gratings include gradually changing shapes, from a top-view perspective, from a central grating having a first non-convex octagonal shape at a center of the grating section to an edge grating having a second non-convex octagonal shape or a convex octagonal shape near an edge of the grating section, wherein the second non-convex octagonal shape is different from the first non-convex octagonal shape. The method further includes manufacturing the grating coupler using the design layout.