Optical Grating Fabrication via Grey-Scale Resist Contouring
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Solution Overview
Problem
Existing methods for fabricating slanted gratings lack flexibility in design, resulting in fixed slope directions and continuous etch depth changes, which limits their optical performance and application in diverse light redirection scenarios.
Innovation Solution
The use of a resist with grey-scale levels to contour trenches in a substrate, allowing for discrete, non-continuous steps and varying trench depths, achieved through e-beam or laser lithography and reactive ion beam etching, enabling enhanced control over grating design and optical performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional methods are used to fabricate slanted gratings, then the manufacturing process is simple, but the design flexibility is limited with fixed slope directions and continuous etch depth changes
Solution Approach 1:
The resist layer is divided into multiple grey-scale levels with discrete depth steps, allowing the grating to be segmented into regions with different trench depths. This segmentation enables independent control of slope direction and depth in different areas, providing design flexibility while maintaining a systematic fabrication process.
Solution Approach 2:
Different regions of the grating are assigned different trench depths and slope characteristics through the grey-scale resist pattern. Each region can be optimized for specific optical performance requirements, such as different diffraction efficiencies or coupling angles, while using the same overall fabrication methodology.
2Reliability
If continuous etch depth changes are used, then the manufacturing process is straightforward, but optical performance is limited in diverse light redirection scenarios
Solution Approach 1:
The continuous etch depth is replaced with discrete depth steps corresponding to different grey-scale levels in the resist. This segmentation allows specific regions to have optimized trench depths for different optical functions, improving overall optical performance while the systematic approach maintains manufacturing feasibility.
Solution Approach 2:
The trench depth parameter is changed from continuous variation to discrete steps defined by the grey-scale levels. This parameter discretization enables precise control over light redirection characteristics in different regions, optimizing optical performance for specific applications like AR/MR displays.
3Adaptability or versatility
If fixed slope directions are used, then the fabrication is straightforward, but adaptability to different light redirection scenarios is reduced
Solution Approach 1:
The grating structure incorporates local variations in slope direction and depth through the grey-scale resist pattern. Different regions can have different tilt angles and depth steps, allowing the same grating to handle multiple light redirection scenarios optimally, such as coupling light into waveguides at different angles for AR/MR applications.
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 provides increased flexibility in grating design, improving optical performance by allowing for varied trench depths and directions, enhancing light redirection efficiency and adaptability in applications like augmented and mixed reality displays.
Implementation Method 1
exposing the resist using e-beam lithography. In some instances, exposing the resist using e-beam lithography includes exposing different areas of the e-beam resist with different exposure doses
Implementation Method 2
the at least one etch includes reactive ion beam etching
Implementation Method 3
exposing the resist using a direct laser writer. Exposing the resist using a direct laser writer can include, for example, exposing different areas of the photoresist to different exposure levels
Data Source
AI summary
The present disclosure describes techniques for fabricating optical elements such as gratings using a resist that can be contoured to have a specified number of grey-scale levels. Optical elements such as gratings, as well as masters that can be used to replicate sub-masters or the optical elements, are described as well.