Slanted Surface-Relief Grating Fabrication via Iterative Refinement
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Solution Overview
Problem
It is challenging to cost-effectively fabricate slanted surface-relief gratings with desired profiles and large slant angles for applications in optical see-through augmented reality systems, as existing methods struggle with precision and durability of master molds used in nanoimprint lithography.
Innovation Solution
A method involving the fabrication of a preliminary master mold followed by fine-tuning processes to modify its duty cycle, height, ridge or groove profile, and surface energy, using techniques such as anisotropic etching and surface treatment, to achieve the desired dimensions and properties for slanted structures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional fabrication methods are used to create slanted surface-relief gratings, then manufacturing cost is reduced, but manufacturing precision and durability of master molds deteriorate
Solution Approach 1:
The patent applies preliminary action by first fabricating a preliminary master mold with approximate grating structures, then iteratively refining it through multiple fine-tuning cycles. Each cycle involves depositing thin material layers and selectively removing portions to gradually achieve the target slanted profile, transforming a single complex high-precision fabrication step into multiple simpler refinement steps.
Solution Approach 2:
The patent employs parameter changes by systematically adjusting fabrication parameters including material layer thickness, deposition conditions, and etching/removal parameters across multiple iterations. The duty cycle, depth, and surface energy of the master mold are modified in controlled steps to converge on the desired slanted grating profile, enabling precise control over the final structure geometry.
2Reliability
If existing fabrication techniques are used for master molds, then process simplicity is maintained, but reliability and durability of master molds worsen
Solution Approach 1:
The preliminary master mold is fabricated first with robust approximate structures, then progressively refined. This preliminary structure serves as a durable foundation that can withstand multiple refinement iterations, separating the structural integrity requirement from the precision profiling requirement and thereby improving overall mold durability.
Solution Approach 2:
The patent transitions from attempting to create the final slanted profile in a single dimensional step to building it through multiple layered dimensions. Each deposited layer adds thickness in the vertical dimension, while selective removal sculpts the horizontal profile, creating the slanted structure through dimensional accumulation rather than direct single-step formation.
3Manufacturing precision
If preliminary master mold fabrication is performed followed by fine-tuning processes, then manufacturing precision of slanted structures is improved, but productivity and fabrication time worsen
Solution Approach 1:
The patent applies partial action by performing fine-tuning only on specific parameters (duty cycle, depth, surface energy) of the preliminary mold rather than completely remanufacturing. Each iteration addresses only the parameters that deviate from targets, avoiding unnecessary rework and accelerating the convergence to the final precise structure.
Solution Approach 2:
Systematic parameter changes are implemented where each fabrication iteration targets specific parameter adjustments based on measured deviations from the target profile. By changing only the necessary parameters (thickness, duty cycle, surface energy) in each cycle rather than all parameters simultaneously, the process achieves precision efficiently with minimal redundant steps.
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 enables the precise and cost-effective fabrication of slanted structures with large slant angles, improving the efficiency of light transfer and refractive index variations in optical devices, such as waveguide displays in augmented reality systems.
Implementation Method 1
depositing a spacer layer on the preliminary surface-relief structure
Implementation Method 2
the etching may include plasma etching
Implementation Method 3
surface-treating the spacer layer
Data Source
AI summary
A surface-relief grating includes a base surface-relief grating comprising a plurality of ridges that include a first material, and a second material on only a top surface or a single sidewall of each ridge of the plurality of ridges, where the second material is different from the first material. A method of fabricating the surface-relief grating includes etching or molding a base surface-relief grating that includes a plurality of ridges, depositing a material layer on the plurality of ridges, and selectively etching the material layer to increase a height or a slant angle of an edge of a ridge in the plurality of ridges to make the surface-relief grating that includes the base surface-relief grating.