Grating Coupler Cladding Thickness Optimization
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Solution Overview
Problem
Existing grating structures face limitations in upward emission efficiency due to operation principles, manufacturing difficulties, and high reflection losses, particularly in shallow and asymmetrical designs, and deep grating structures with structural discontinuities.
Innovation Solution
A grating structure with a core layer and multiple cladding layers, where the concavities are filled with the same material as the first upper cladding layer, and the thicknesses of the layers are optimized to enhance upward emission efficiency, with the first upper cladding layer's thickness determined by subtracting the depth of the concavity and convexity multiplied by ½ from the wavelength, and the second upper cladding layer's thickness determined by multiplying the wavelength by (m2/2±⅛), facilitating easy manufacturing and reducing reflection losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a shallow grating structure is used, then the manufacturing is easier, but the upward emission efficiency is insufficient
Solution Approach 1:
The patent uses a composite structure combining silicon core layer with silicon oxide cladding layers of specific thicknesses. The silicon oxide layers with optimized thicknesses (first layer: λ/(2n1)±λ/(8n1), second layer: λ/(4n2)±λ/(8n2)) create constructive interference for upward emission while maintaining manufacturability through standard semiconductor processing techniques.
Solution Approach 2:
The patent optimizes specific parameters including the thickness of silicon oxide cladding layers, the depth of grating grooves, and the period of the diffraction grating. By adjusting these parameters to satisfy specific mathematical relationships with the wavelength, the upward emission efficiency is significantly improved without requiring complex manufacturing processes.
2Reliability
If an asymmetrical grating structure is used, then the upward emission efficiency is improved, but the manufacturing difficulty increases
Solution Approach 1:
The patent employs a symmetrical composite structure with silicon core and silicon oxide cladding layers. This symmetrical design maintains ease of manufacture through standard fabrication processes while achieving high upward emission efficiency through optimized layer thicknesses and grating parameters that satisfy specific optical interference conditions.
3Reliability
If a deep grating structure is used, then the upward emission efficiency is improved, but the reflection loss increases
Solution Approach 1:
The patent introduces silicon oxide cladding layers as intermediary layers between the silicon core and the external environment. These intermediary layers with optimized thicknesses reduce reflection losses by creating gradual impedance matching, while the grating structure on the silicon core maintains high upward emission efficiency.
Solution Approach 2:
The composite structure of silicon core with silicon oxide cladding layers reduces reflection losses while maintaining high upward emission efficiency. The specific thickness relationships of the cladding layers with the wavelength create constructive interference for upward emission and minimize reflective losses at the interfaces.
4Ease of manufacture
If the grating structure has structural discontinuities, then the manufacturing is simpler, but the reflection loss increases
Solution Approach 1:
The patent uses a continuous composite structure with silicon core layer and silicon oxide cladding layers. This continuous structure maintains ease of manufacture through standard deposition and etching processes while minimizing reflection losses through optimized interface continuity and specific layer thickness relationships.
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 grating structure achieves improved upward emission efficiency while being easier to manufacture and reducing reflection losses, enhancing the performance of grating couplers.
Implementation Method 1
a diffraction grating is formed on the core layer 114... a part of guided light is diffracted and emitted
Implementation Method 2
the thickness from a top surface of a convexity in the concavity and convexity part to a top surface of the first upper cladding layer is: a value obtained by subtracting, from a wavelength of light in the material forming the first upper cladding layer multiplied by ((2m1−1)/4±1⁄8)...
Data Source
AI summary
A grating structure for a grating coupler is provided which has a high efficiency resulting from the operating principle, is easily manufactured, and simultaneously has little reflection loss. This grating structure is provided with a core layer having periodic recesses and protrusions formed on the upper surface, a first upper cladding layer in contact with the upper surface of the core layer, a second upper cladding layer in contact with the upper surface of the first upper cladding layer, and a first lower cladding layer in contact with the lower surface of the core layer. The recessed portions of said recesses and protrusions are filled with the same material as the first upper cladding layer. The refractive index of the material forming the core layer is greater than the refractive index of the materials forming the first upper cladding layer, the second upper cladding layer and the first lower cladding layer. The refractive index of the material of the first upper cladding layer is greater than the refractive index of the material of the second upper cladding layer. The thickness from the upper surface of the protruding portions of the recesses and protrusions to the upper surface of the first upper cladding layer is within the range obtained by subtracting ½ of the depth of the recesses and protrusions from ((2m1−1)/4±⅛) times (m1 being a positive integer) the wavelength, in the material forming the first upper cladding layer, of light inputted and outputted by the grating coupler.