Waveguide Fabrication via Master Grating Edge Etching
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Solution Overview
Problem
The fabrication of waveguides with large diffraction gratings is challenging due to the difficulty in achieving high image quality, as protrusions from the master grating tool edges result in refractive index mismatches between replication and lamination layers, causing light deviation and secondary image formation.
Innovation Solution
A method involving a single master grating tool with minimal edge protrusions is used, where photoresist layers are coated and patterned with laser-derived interference patterns, and etched to create grating profiles without significant edges, followed by replication and lamination with UV-curable polymers to ensure matching refractive indices and eliminate light deviation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a master grating tool is used to replicate diffraction gratings in a waveguide, then the waveguide can convey light and expand the pupil, but protrusions from the master grating tool edges cause refractive index mismatches that lead to light deviation and secondary image formation
Solution Approach 1:
The patent extracts and removes the problematic edge protrusions from the master grating tool through selective etching processes. The method involves etching the master grating tool to create a relief structure where the edges are removed or minimized, preventing the formation of protrusions that cause refractive index mismatches. This extraction of the harmful element (edge protrusions) directly resolves the contradiction by eliminating the source of light deviation while preserving the functional grating structure.
Solution Approach 2:
The patent applies preliminary action by pre-processing the master grating tool with selective etching before replication. The edge removal process is performed in advance on the master tool, ensuring that when the UV-curable polymer is replicated, no protrusions are formed. This preliminary modification of the master grating tool prevents the harmful effect from occurring in the first place, maintaining both image quality and manufacturing feasibility.
2Adaptability or versatility
If large diffraction gratings are fabricated in large waveguides, then the waveguide can provide a greater range of eye positions and act as a combiner, but achieving the required tolerances for high image quality becomes increasingly challenging
Solution Approach 1:
The patent applies segmentation by dividing the master grating tool fabrication into distinct etching stages. The process segments the grating formation into: (1) initial pattern transfer, (2) selective etching to create relief structure, and (3) edge removal to eliminate protrusions. This segmented approach allows each step to be optimized independently, making it feasible to manufacture large gratings with the required precision tolerances for high image quality while maintaining the large size needed for extended eye box and combiner functionality.
3Reliability
If refractive index mismatch occurs between replication and lamination layers, then light deviation and secondary image formation occur, but eliminating this mismatch requires precise control of replication layer thickness and edge removal
Solution Approach 1:
The patent replaces mechanical measurement and control methods with a chemically-driven self-regulating etching process. Instead of relying on precise mechanical control of replication layer thickness and manual edge removal, the process uses selective chemical etching that automatically removes material down to a predetermined depth. This substitution of chemical processes for mechanical control simplifies the fabrication process while achieving the required precision to eliminate refractive index mismatches and prevent light deviation.
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 eliminates light deviation and secondary image issues by ensuring no significant protrusions in the replication layer, enhancing the diffraction efficiency and image quality of the waveguide.
Implementation Method 1
The UV-curable polymer is then cured with UV light
Implementation Method 2
photoresist layers are coated and patterned with laser-derived interference patterns
Implementation Method 3
etched to create grating profiles without significant edges
Data Source
Figure 1a
Figure 1b
Figure 1c
AI summary
There is provided a method for fabricating a waveguide. The method comprising fabricating a first master grating tool comprising a first tool substrate having a surface with an area corresponding at least to the area of a surface of the waveguide and having a first grating profile formed over substantially all of the surface of the first tool substrate. Fabricating a second master grating tool comprising a second tool substrate having a surface with an area corresponding at least to the area of the surface of the waveguide and having a second grating profile formed over substantially all of the surface of the second tool substrate. Using the first master grating tool to replicate the first grating profile over substantially all of a surface of a first waveguide substrate. Using the second master grating tool to replicate the second grating profile over substantially all of a surface of a second waveguide substrate. Applying a first dielectric layer over a selected area of the first grating profile replicated on the surface of the first waveguide substrate. Applying a second dielectric layer over a selected area of the second grating profile replicated on the surface of the second waveguide substrate. Applying a layer of laminating material to at least one of the surfaces of the first and second waveguide substrates and bringing the surfaces of the first and the second waveguide substrates together thereby to join the first and second waveguide substrates together by an intermediate lamination layer.