Bi-Layer Grating Coupler Structure for Low-Loss Laser Coupling
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Solution Overview
Problem
Conventional grating couplers with non-wafer bonded configurations suffer from inefficient light coupling due to high insertion loss and limited power transfer, primarily because the E-field intensity is localized in lower refractive index layers, leading to reduced coupling efficiency both on-chip and off-chip.
Innovation Solution
A high-efficiency grating coupler with a wafer bonded configuration is developed, where the silicon etched layers are positioned above the polycrystalline silicon nitride layer, allowing for constructive reflection and increased E-field intensity in higher refractive index layers, enhancing coupling efficiency through a bi-layer grating structure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a non-wafer bonded configuration is used, then the device complexity is reduced, but the light coupling efficiency deteriorates due to high insertion loss
Solution Approach 1:
The grating structure is divided into multiple silicon layers with different etching patterns, creating a multi-level grating configuration that segments the light coupling function across different layers to improve overall coupling efficiency
Solution Approach 2:
The invention transitions from a planar single-layer grating to a three-dimensional multi-layer stacked grating structure, adding the vertical dimension to enhance light coupling by creating multiple interaction planes between light and grating elements
2Ease of manufacture
If the E-field is localized in lower refractive index layers, then the manufacturing process is simplified, but the power transfer efficiency deteriorates
Solution Approach 1:
Different silicon layers are assigned different etching depths and patterns, creating local variations in grating structure that optimize E-field distribution in specific regions to enhance power transfer while maintaining manufacturing feasibility
Solution Approach 2:
The grating structure combines multiple silicon layers with different optical properties and etching characteristics, creating a composite grating system that optimizes both power transfer efficiency and manufacturing considerations
3Ease of manufacture
If a single-layer grating is used, then the manufacturing process is simpler, but the coupling efficiency is reduced
Solution Approach 1:
The grating function is segmented across multiple silicon layers, with each layer contributing to the overall coupling efficiency through its specific etching pattern, thereby achieving high performance without excessive manufacturing complexity
Solution Approach 2:
Multiple grating layers are stacked vertically with each layer nested above the previous one, creating a compact multi-level structure that achieves enhanced coupling efficiency within a vertically integrated fabrication process
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 wafer bonded configuration significantly improves light coupling efficiency by localizing the E-field in higher refractive index layers, enabling more power to be scattered upwards, thus achieving higher directionality and broader bandwidth compared to non-wafer bonded configurations.
Implementation Method 1
allowing for constructive reflection and increased E-field intensity in higher refractive index layers
Implementation Method 2
increased E-field intensity in higher refractive index layers
Implementation Method 3
enabling more power to be scattered upwards
Implementation Method 4
a bi-layer grating disposed above the silicon nitride layer. The bi-layer grating includes a first etched layer of the first silicon layer and a second etched layer of the second silicon layer
Data Source
AI summary
A grating coupler with a wafer bonded configuration includes: a substrate; an oxide layer disposed on the substrate; a silicon nitride layer disposed above the oxide layer; a first silicon layer disposed above the silicon nitride layer; a second silicon layer disposed above the first silicon layer; and a bi-layer grating disposed above the silicon nitride layer. The bi-layer grating includes (i) a first etched layer of the first silicon layer and (ii) a second etched layer of the second silicon layer.