Apodized Two-Dimensional Grating Coupler for TE/TM Coupling
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Solution Overview
Problem
The challenge of improving the coupling efficiency of optical data links in semiconductor devices is exacerbated by polarization-dependent loss (PDL) due to mode mismatch and device size constraints in existing grating couplers.
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-polarization gratings that adapt to energy distribution and minimize PDL.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional grating coupler designs are used, then device size can be reduced, but coupling efficiency deteriorates due to polarization-dependent loss
Solution Approach 1:
The grating coupler is divided into multiple discrete grating elements arranged in an array, where each grating element can be independently designed and optimized. This segmentation allows the system to handle different polarization modes (TE and TM) separately through tailored grating geometries, thereby improving overall coupling efficiency while managing device complexity through modular design
Solution Approach 2:
Different regions of the grating array employ locally optimized grating patterns with varying geometries, periods, and orientations. Specifically, the patent uses different grating designs for TE-mode coupling versus TM-mode coupling, with each region's grating parameters (such as duty cycle, depth, and shape) locally tuned to maximize coupling efficiency for the intended polarization mode, thus resolving the PDL issue
2Productivity
If grating coupler size is reduced to meet device size constraints, then integration density improves, but coupling efficiency deteriorates
Solution Approach 1:
The patent transitions from conventional one-dimensional linear grating arrays to two-dimensional planar grating arrays with elements arranged in both x and y directions. This dimensional expansion allows light coupling to occur from multiple spatial directions simultaneously, effectively increasing the coupling aperture and efficiency without proportionally increasing the linear device footprint, thus improving integration density while maintaining high coupling efficiency
Solution Approach 2:
The grating coupler design incorporates multi-functional grating elements that can simultaneously support both TE and TM polarization modes through carefully engineered geometries. Some grating elements are designed with dual functionality to couple both polarization types, while others are specialized for specific modes. This universal design approach allows the compact structure to handle multiple functions (different polarizations) within a reduced size, thereby improving integration density without sacrificing coupling efficiency
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 enhances optical coupling efficiency while reducing PDL, ensuring effective transmission of both transverse electric (TE) and transverse magnetic (TM) modes.
Implementation Method 1
a grating section configured to be optically coupled to an optical fiber
Implementation Method 2
a taper section comprising a pair of tapers configured to transmit light of different polarizations
Data Source
AI summary
A method of forming a grating coupler includes: providing an initial design layout of the grating coupler, wherein the initial design layout includes: a taper section, comprising a pair of tapers; and a grating section coupled to the taper section, the grating section having an array of gratings, wherein the gratings includes gradually changing shapes, from a top-view perspective, from a first non-convex octagonal shape of a central grating, at a center of the grating section, of one of a second non-convex octagonal shape, a convex octagonal shape, and a quadrilateral shape, to an edge grating near an edge of the grating section. The method further includes: converting the initial design layout into a revised design layout through an optical proximity correction operation; and manufacturing the grating coupler using the revised design layout.