Optical Waveguide Groove Structure for High Diffraction Efficiency
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Solution Overview
Problem
Forming deep grooves in optical waveguide layers made of hard-etching materials is difficult, leading to reduced optical characteristics such as diffraction efficiency, which requires a larger number of grooves and a larger optical element size.
Innovation Solution
An optical element with an optical waveguide layer of thickness 1.5µm or greater, featuring a periodic structure of grooves with an aspect ratio of 2.5 or greater, where the depth of the grooves is less than 600nm and the pitch is between 150nm and 480nm, and the angle of the side surfaces relative to the bottom surface is 80° or greater, allowing for enhanced diffraction efficiency with a reduced number of grooves.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If shallow grooves are formed in a thin layer of the optical waveguide layer, then the etching process becomes easier, but the optical characteristics such as diffraction efficiency are lowered
Solution Approach 1:
The invention transitions from forming grooves in thin layers (2D constraint) to forming grooves in thick layers (utilizing the third dimension - depth). By increasing the optical waveguide layer thickness to 1.5µm or more and forming grooves with depth of less than 600nm, the aspect ratio becomes 2.5 or more, which enhances diffraction efficiency while maintaining etchability through the thick layer.
Solution Approach 2:
The invention changes critical parameters: layer thickness from thin to 1.5µm or more, groove depth to less than 600nm, and aspect ratio to 2.5 or more. These parameter changes enable simultaneous achievement of easy etching and high optical characteristics by optimizing the relationship between layer thickness and groove depth.
2Reliability
If the number of grooves is increased to improve optical characteristics, then diffraction efficiency improves, but the size of the optical element becomes larger
Solution Approach 1:
By changing the groove depth parameter to less than 600nm in a thick layer (1.5µm or more), the aspect ratio reaches 2.5 or more. This parameter optimization enhances diffraction efficiency per groove, allowing fewer grooves to achieve the desired optical performance, thereby reducing the optical element size.
3Reliability
If deep grooves are formed in the optical waveguide layer made of hard-etching material, then the optical characteristics are improved, but the etching process becomes difficult
Solution Approach 1:
The invention optimizes the parameter relationship by forming grooves with depth of less than 600nm in an optical waveguide layer of 1.5µm or more thickness. This creates an aspect ratio of 2.5 or more that balances etchability with optical performance, making the etching process feasible while achieving high diffraction 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
This approach enhances optical characteristics like diffraction efficiency while reducing the number of grooves and downsizing the optical element, facilitating more efficient light manipulation and device compactness.
Implementation Method 1
an optical element 5 comprising an optical waveguide layer 53, the optical waveguide layer including a periodic structure of grooves 61
Data Source
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Figure 3
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AI summary
An object is to realize an optical characteristic based on periodic structure of optical waveguide layer of optical element, while reducing the number of grooves in the periodic structure in the optical waveguide layer. An optical element 5 includes an optical waveguide layer 53 that is provided with a periodic structure 6 of grooves 61. The optical waveguide layer 53 has a layer-thickness equal to or greater than 1.5µm and is made of material selected from a group consisting of Ta2O5, Al2O3, LiNbO3, LiTaO3, AlN, GaN, SiC, and Yttrium aluminum garnet (YAG). (D/0.5Λ)≧2.5 is satisfied, where D indicates the depth of the groove; and A indicates the pitch of the arranged grooves, the unit of A being identical to the unit of D.